Environmental Impact of Stressors (Sustainability Assessment)

INPRO basic principle in the area of environmental impact of stressors: The expected adverse environmental

effects of an NES should be well within the performance envelope of current NESs delivering similar energy products.

Introduction

Objective

This volume of the updated INPRO Manual provides guidance to the assessor of an NES (or a facility thereof) that is planned to be installed, describing how to apply the INPRO methodology in the area of environmental impact of stressors. The INPRO assessment should either confirm the fulfilment of all INPRO methodology environmental CRs, or identify gaps (non-compliance with the INPRO methodology CRs) requiring corrective actions (including research, development and demonstration (RD&D)) to achieve long term sustainability of the NES assessed. The INPRO assessor (or team of assessors) is assumed to be knowledgeable in the area of environmental impact of stressors and/or may be using the support of qualified national or international organizations (e.g. the IAEA) with relevant experience.
Two general types of INPRO assessor can be distinguished: a nuclear technology holder (i.e. designer, developer or supplier of nuclear technology) and a (potential) user of such technology. The role of the latter type of assessor, i.e. a technology user, is primarily to check, in a simplified manner, whether the designer (supplier) has appropriately taken into account the environmental aspects in the design as defined by the INPRO methodology. A technology user is assumed to be primarily interested in proven technology to be installed in his or her country in the near future. A designer (developer) performing an INPRO assessment can use this current publication to check whether the (innovative) design under development, which is expected to comply with the existing IAEA safety standards, meets the INPRO methodology environmental requirements for the assessment of sustainability of NES, and can additionally initiate modifications during early design stages, if necessary, to improve the environmental performance of the design.
In INPRO sustainability assessment, the term ‘technology user’ does not refer to an independent national nuclear regulatory authority. INPRO sustainability assessment is most often part of strategic nuclear energy planning. Typically, this planning activity is performed by national energy ministries, utilities (government or privately held) and/or their various technical support organizations. In INPRO terminology, the ‘technology user’ is either the country (in a generic sense) or, more specifically, the owner and/or operator of the technology. The ‘technology holder or designer’ is the engineering company (government or privately held) that holds the intellectual property rights on the technology. When discussing the specific context where trade agreements between countries restrict or control transfers and uses of technology, the INPRO use of the term ‘technology holder’ may also refer to the government under which the technology is ‘flagged’.
An assessor in a country embarking on a nuclear power programme has several options when using the INPRO methodology that depend on the stage of the programme (see the introductory manual of the updated INPRO methodology).
Every nuclear facility needs an EIA in order to be licensed and to become operational. The INPRO environmental assessment is not intended to substitute this licensing activity, but should rather demonstrate that the NES assessed is sustainable in the long term with regard to its environmental impact. Application of the INPRO methodology cannot substitute fulfilment of any of the existing national requirements in this area. However, INPRO CR determined in this publication follow the requirements of the IAEA safety standards, in particular, IAEA Safety Standards Series No. GSR Part 3, Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards [2].

Scope

Environmental impact from NES involves two large groups of factors. One group impacting the environment comprises the consumption of non-renewable resources including both fissile/fertile materials necessary to produce nuclear fuel and other materials (e.g. zirconium). All these factors and consumption of electricity necessary to construct, operate and occasionally decommission NES installations are considered in the INPRO methodology manual on environmental impact from depletion of resources [3].
Another group comprises radiological, chemical, thermal and other stressors which NESs release into environment. This group also includes water intake because this factor can be important for biota even when this water is returned to the environment in a clean form (e.g. as steam from nuclear power plant cooling towers). All these factors are considered in this INPRO methodology manual on environmental impact of stressors.
The INPRO methodology in the area of environmental impact of stressors covers only normal operation and anticipated operational occurrences of NES facilities. Consequences of potential accidents are discussed in the INPRO methodology manuals in the areas of safety of reactors and safety of the nuclear fuel cycle. Guidance provided here, describing good practices, represents expert opinion but does not constitute recommendations made on the basis of a consensus of Member States

Structure

In Section 2, general features of an environmental assessment are presented.
In Section 3, an overview of information that must be available to an INPRO assessor to perform the environmental assessment is provided.
In Section 4, the background of the INPRO methodology BP for environmental impact of stressors, and the corresponding URs and CRs, consisting of INs and ALs, are presented. At the CR level, guidance is provided on how to determine the values of the INs and ALs.
Appendix I provides general information on types of stressor and separate, illustrative lists of stressors (in the form of tables) for all facilities of an NES based on uranium and mixed oxide (MOX) fuel (as an example). This appendix could be used by an INPRO assessor as a starting point to generate input for the BP evaluation.
Appendix II presents simplified environmental analysis methods of how to calculate the impact of radiological stressors, i.e. the dose on humans and non-human biota (plants and animals). It also briefly discusses the calculation of the impacts of chemical stressors on humans and non-human biota.
Appendix III illustrates the concepts for optimization of the management options for reduction of the environmental impact of nuclear facilities.
Appendix IV provides basic information on the concept of collective dose, which is used in the INPRO assessment method described in this publication.
Table 1 provides an overview of the BP, URs and CR in the INPRO methodology area of environmental impact of stressors.

Table 1. Overview of basic principle, user requirements and criteria in the INPRO methodology area of environmental impact of stressors

INPRO basic principle the area of environmental impact of stressors (acceptability of expected adverse environmental effects): The expected adverse environmental effects of an NES should be well within the performance envelope of current NESs delivering similar energy products.
INPRO user requirements	Criteria	Indicator (IN) and Acceptance Limit (AL)
UR1: Controllability of environmental stressors: The environmental stressors from each facility of an NES over the complete life cycle should be controllable to levels meeting or below current standards	CR1.1: Radiation exposure of the public	IN1.1: Dose to the public
		AL1.1: Lower than the dose constraint
	CR1.2: Radiation exposure of non-human species	IN1.2: Doses to the reference biota species
		AL1.2: Lower than international recommendations
	CR1.3: Impacts of chemicals and other non-radiation environmental stressors	IN1.3: Levels of chemicals and other stressors
		AL1.3: Lower than national environmental safety standard levels
UR2: Reduction of total environmental impact of emitted radioactivity: Total radiotoxicity of radionuclides discharged by the NES assessed should be lower than that of any current NES delivering similar energy products	CR2.1: Reduction of environmental impact of radiation	IN2.1: Total radiotoxicity of radionuclides emitted to the environment from the NES assessed (RT)
		AL2.1: RT is lower than the radiotoxicity of stressors emitted to the environment from a current NES delivering similar energy products
UR3: Optimization of the measures to reduce environmental impact: The measures applied to reduce adverse environmental impact attributable to an NES should be optimized	CR3.1: Optimization of the measures to reduce environmental impact	IN3.1: Measures to reduce environmental impact of the NES
		AL3.1: Measures are optimized

Concept of sustainable development and its relationship with the area of environmental impact of stressors of the INPRO methodology

The United Nations World Commission on Environment and Development Report [4] (often known as the Brundtland Report), entitled Our Common Future, defines sustainable development as: “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (see chapter 2, para. 1 [4]). This definition contains within it two key concepts:

“

• the concept of ‘needs’, in particular the essential needs of the world’s poor, to which overriding priority should be given; and
• the idea of limitations imposed by the state of technology and social organization on the environment’s ability to meet present and future needs.”

Based on this definition of sustainable development, a three part test for any approach to sustainability and sustainable development was proposed within INPRO project: (i) current development should be fit for the purpose of meeting current needs with minimized environmental impacts and acceptable economics; (ii) current RD&D programmes should establish and maintain trends that lead to technological and institutional developments that serve as a platform for future generations to meet their needs; and (iii) the approach to meeting current needs should not compromise the ability of future generations to meet their needs.
At first reading, this definition may appear obvious, but when considering the complexities of implemented nuclear energy technology and systems, plus their many supporting institutions, meeting the three part test is not always straightforward because many approaches only meet one or perhaps two parts of the test in a given area, and may fail on the others.
The Brundtland Report overview (para. 61 [4]) of the topic of nuclear energy summarized that:

“After almost four decades of immense technological effort, nuclear energy has become widely used. During this period, however, the nature of its costs, risks, and benefits have become more evident and the subject of sharp controversy. Different countries world-wide take up different positions on the use of nuclear energy. The discussion in the Commission also reflected these different views and positions. Yet all agreed that the generation of nuclear power is only justifiable if there are solid solutions to the unsolved problems to which it gives rise. The highest priority should be accorded to research and development on environmentally sound and ecologically viable alternatives, as well as on means of increasing the safety of nuclear energy.”

The Brundtland Report presented its comments on nuclear energy in chapter 7, section III [4]. In the area of nuclear energy, the focus of sustainability and sustainable development is on solving certain well known problems (referred to here as ‘key issues’) of institutional and technological significance. Sustainable development implies progress and solutions in the key issue areas. Seven key issues are discussed (in this order):
(a) Proliferation risks;
(b) Economics;
(c) Health and environment risks;
(d) Nuclear accident risks;
(e) Radioactive waste disposal;
(f) Sufficiency of national and international institutions (with particular emphasis on intergenerational and transnational responsibilities);
(g) Public acceptability.
The INPRO methodology for the self-assessment of sustainability and sustainable development of an NES is based on the broad philosophical outlines of the Brundtland Report’s concept of sustainable development described above. Twenty-nine years have passed since the publication of the Brundtland Report, and 15 years have passed since the initial consultancies on development of the INPRO methodology in 2001. In the interim period of time, significant historical events have starkly highlighted certain key issues. However, the key issues for sustainable development of NESs have remained essentially unchanged over nearly three decades.
By far the most notable events in the period, which have a direct impact on nuclear energy sustainability, are related to non-proliferation, nuclear security, cost escalation of new construction and, most notably, the accident at the Fukushima Daiichi nuclear power plant in 2011. The Fukushima Daiichi accident further clarified that nuclear safety is an issue of paramount importance for sustainability and that external hazards, associated with a particular site, could be responsible for a dramatic common cause failure involving multiple reactor units.
In each INPRO methodology manual, a key issue of NES sustainable development is examined. The structure of the methodology is a hierarchy of INPRO BPs, URs and CRs measuring whether the UR has been achieved. Under each BP, the CRs include measures that take into consideration the three part test based on Brundtland Report’s definition of sustainable development which was described above.
This INPRO Manual focuses on the key issue of environmental stressors (radioactive, chemical, heat and others) associated with NES development and deployment. It does not consider emissions of environmental stressors under accident conditions. The topics of radioactive and chemical emissions during accidents are covered under the INPRO areas of safety of reactors and fuel cycle facilities and are published in separate manuals.
In the broad sense of the full related technology chain, NESs are comparatively benign with respect to many stressor emissions when compared to available, baseload non-NESs. For example, because the waste products of nuclear fission are contained during all but severe nuclear accidents, releases of radiological species to the environment from operating nuclear reactors are typically extremely small — at least one and often two or more orders of magnitude below national regulatory limits and international standards [5]. In fact, radioactive emissions from coal fired thermal power plants are often higher than for nuclear reactors of comparable scale. This is because the coal and the resulting fly ash waste contain uranium and thorium oxides and radioactive progenies that are not fully captured by emission controls. Chemical stressor emissions from nuclear reactors are also very small, whereas chemical stressors (sulphur oxides, nitrogen oxides (NOX), mercury, dioxins, volatile aromatic hydrocarbons, etc.) can be significant fugitive components of emissions from coal fired power plants. Although far cleaner than coal, natural gas fired plants contribute significant emissions of NOX and emissions of methane associated with fuel leaks. If carbon emissions are considered as an environmental stressor (an increasingly common position globally), nuclear power is benign and comparable to renewable energy power sources such as hydroelectricity.
Typically, the largest shares of radiological and chemical stressor emissions from NESs originate from mining, milling and spent fuel reprocessing fuel cycle facilities, as opposed to from nuclear reactors. One area where nuclear power has similar environmental stressor impacts to other fossil fuel generation technologies is waste heat rejection. More recently, advances such as supercritical coal and combined cycle natural gas plants have increased thermal efficiency and thereby reduced the waste heat impacts and cooling water use per unit of electricity produced by fossil fuel generation technology. However, if evaporative cooling towers are used, these impacts can often be mitigated in both nuclear and fossil fuel generation technologies. Next generation nuclear reactors also promise significant increases in thermal efficiency, and certain high temperature plant designs may allow practical air cooling.
This current INPRO Manual tests whether an NES is sustainable with respect to environmental stressors. In the case of each NES installation, radiation exposure of the public is compared to the dose constraints. Radiation exposure of non-human species is compared to the lowest values of international standards or national regulations (when available). The total radiotoxicity of emissions is also evaluated as a broad metric to consider the reduction of radiological impact on the environment. Moreover, the manual requests, in UR3, that evidence of optimization of measures to reduce environmental impact is provided. Suggested optimization approaches include best available techniques (BATs), best environmental practice (BEP), as low as reasonably achievable (ALARA) or as low as reasonably practicable (ALARP), with social and economic factors taken into account.
As previously mentioned, environmental stressor impacts tend to be primarily associated with certain fuel cycle facilities that are not broadly distributed. These facilities are often part of national economies of nuclear fuel suppliers and service States that provide fuels and services as an export to other national economies. In certain cases, it may be appropriate to parse available results of environmental assessments of these facilities to consider separately the fraction of stressor emissions associated with national nuclear power generation and of exported nuclear fuels and services. The INPRO CRs in this manual are set as total dose constraints and other types of recommended or required thresholds. The sustainability requirements in the INPRO area of environmental impact of stressors are fulfilled when all ALs are met, but it is also important to understand the balance of environmental impacts accepted in exchange for domestic power generation (a broad public good) and in exchange for exported nuclear fuel products and services (potentially a narrower or broader public good, depending upon the tax/tariff structures associated with the industry). Understanding this balance is a central question in cost–benefit analysis (CBA) regarding development of the national NES, which is discussed in the INPRO methodology area of infrastructure [6].
The NES is expected to meet the three part test based on the Brundtland Report’s definition of sustainable development if all ALs in all areas are met as outlined in the INPRO methodology.
Protection of the environment is a major consideration in the processes for approving industrial activities in many countries. The level of societal concern for the environment internationally is clearly indicated in several documents, in addition to the Brundtland Report [4], reflecting international consensus, notably the Rio Declaration on sustainable development [7], i.e. the Rio Declaration on Environment and Development, Agenda 21, the Statement on Sustainable Development of Forests, the United Nations Framework Convention on Climate Change and the Convention on Biological Diversity. Other related documents are the United Nations resolution on institutional arrangements for the Implementation of the Global Programme of Action for the Protection of the Marine Environment from Land-based Activities [8], the Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management [9], the IAEA Convention on Nuclear Safety [10], the Convention on Environmental Impact Assessment in a Transboundary Context (Espoo Convention) [11], the Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (London Convention) [12], the Convention for the Protection of the Marine Environment of the North-East Atlantic [13] and the European Commission recommendation on standardized information on radioactive airborne and liquid discharges into the environment from nuclear power reactors and reprocessing plants in normal operation [14].
Legacy of the past
In some cases, the legacy of the past may still burden the civil nuclear industry (e.g. Refs [15–20]). If the nuclear industry in general claims its sustainability, this should be achieved for all of its facilities to prevent objective criticism that may challenge the assertion (e.g. imported uranium used in a sustainable NES should come from a mining/milling operation that complies with environmental standards at the time that the uranium for the NES was extracted).

General features of an environmental assessment

This section provides some general background information on environmental issues, particularly on the environmental impact of stressors caused by an NES.

Concept of sustainable development

The concept of sustainability can be considered from several related, but different, points of view: social, economic, environmental and institutional. This publication deals with the environmental dimension of sustainability by considering stressors providing adverse impact to the environment.
Protection of the environment is a major consideration in the processes for approving industrial activities in many countries. The level of international societal concern for the environment is clearly indicated in publications reflecting international consensus, notably the Brundtland Report [4], the Rio Declaration on sustainable development [7] and the Joint Safety Convention of the IAEA [9].
The common basic idea in these publications is that the present generation should not compromise the ability of future generations to fulfil their needs and should leave them with a healthy environment. Nuclear power should support sustainable development by providing much needed energy with relatively low burdens on the atmosphere, water, land and resource use. Improvement of the technology should include improvement of its environmental aspects to a degree that is consistent with importance to society and with the potential environmental performance of competing technologies.

Interfaces of a nuclear energy system with the environment

An example of the different components or facilities of a complete NES is presented in Fig. 1, starting with mining and processing, through to the final disposal of nuclear waste.

FIG. 1. Interfaces of a nuclear energy system with the environment.

An NES has several interfaces with the environment and other industries. From the environment, non-renewable resources such as fissile and fertile materials, e.g. uranium and thorium (orange arrow in Fig. 1), are removed and used in the NES, together with other non-renewable materials such as zirconium (bright yellow arrow in Fig. 1). On the other hand, the NES releases some stressors, e.g. radioactive nuclides, that have an adverse impact on the environment (pale yellow arrow in Fig. 1). In addition to these environmental effects, an NES is exchanging with other industries energy and industrial materials required for the installation, operation and finally decommissioning of the nuclear facilities (blue arrow in Fig. 1).

Performance of an environmental analysis

Figure 2 provides a general overview of how to perform an environmental impact analysis in steps.

FIG. 2. Flow chart of an environmental stressor analysis (adapted from Ref.).

Starting from the definition of sources, i.e. the facilities of the NES, the stressors from the sources are identified, the pathways of the stressors to the receptors analysed, leading to the end point of the environmental analysis, i.e. the impact/effect of the stressors on the recipients. As shown in Fig. 2, Stressors of NES facilities include radioactive and non-radioactive chemical toxic emissions, heat discharges, noise, impacts on some non-renewable resources, and water and land use, all with potentially adverse environmental effects, which may occur on a local, regional or even global scale.
The actual environmental effects attributable to stressors may differ significantly with geographical location and other site specific and project specific factors of the NES facilities. However, all things being equal, the lower the level (magnitude) of a stressor, the lower will be the resultant environmental effect. Moreover, the stressors, as opposed to environmental pathways and receptors, are more under the control of the designers of the NES.
Comparison between nuclear and non-nuclear energy systems
The results of sustainability assessment of NESs in the area of environmental impact of stressors can be used in comparison with other non-nuclear energy systems only when they both have been analysed to a similar depth. For example, some environmental stressors (e.g. greenhouse gases) that may be negligible in an NES need to be kept in the list of stressors, enabling a comparison between different sources of power generation.

Types of stressor in a nuclear energy system

Any energy system will inevitably introduce stressors to the environment, such as release of radionuclides or non-radioactive chemicals, and depletion of resources, with potentially adverse environmental effects (or impacts) on a local, regional or even global scale.
The environment is considered to be composed of interacting systems, which, in turn, comprise biological elements, i.e. fauna and flora, and physical elements, i.e. atmosphere, land, water and resources (e.g. used for energy production). Impacts are considered to be those effects that alter the existing environment, either temporarily or permanently.
The adverse environmental impacts usually covered in an EIA as part of the site licensing process include health effects on people and non-human species. Both radiological and non-radiological (chemical) health effects are considered. Trade-offs and synergies among the effects from different energy system components and different environmental stressors are also considered, if possible.
Radionuclides discharged by an NES are stressors that are specific to (but not exclusive to) nuclear power; in many cases, the public concerns on NES safety are related to the release of radionuclides into the environment. At the same time, there are many other stressors such as toxic chemicals (e.g. acid mine drainage from waste rock), heat rejections from once through cooling systems, land use, etc., that, in specific cases, might have a greater negative impact than radionuclides released into the environment.

Regulatory standards for radiological stressors

For planned exposure situations, which is the case for the environmental INPRO assessments, exposures and risks are subject to control to ensure that the specified dose limits for occupational exposure and those for public exposure are not exceeded, and optimization is applied to attain the desired level of protection and safety. Paragraph 1.22 of GSR Part 3 [2] recommends that dose constraints are to be used “for optimization of protection and safety, the intended outcome of which is that all exposures are controlled to levels that are as low as reasonably achievable, economic, societal and environmental factors being taken into account”. It is further clarified that [2]:

“Dose constraints are set separately for each source under control and they serve as boundary conditions in

defining the range of options for the purposes of optimization of protection and safety. Dose constraints are not dose limits: exceeding a dose constraint does not represent non-compliance with regulatory requirements,

but it could result in follow-up actions.”

Although the dose limits, expressed as an annual effective dose to the representative person, are generally set at the level of 1 mSv, dose constraints are quite different in different countries (see Table 12, in Section II.2.3). It should be emphasized that there are no constraints for the release of individual radionuclides. There is also no international recommendation on the limits for concentrations of radionuclides in the environment. On the other hand, there are so called reference (or authorized discharge limits [22]) levels for radionuclide discharges into the environment. These reference levels are facility and site specific, and are the result of environmental analyses with the objective to identify, with sufficient conservatism, allowable emission rates of radionuclides, so as to not exceed dose limits.
Primarily, the effective dose to human population/non-human species can be considered as an indicator of environmental impact of radiation release. Ambient radionuclide concentrations in terms of both individual radionuclides and total alpha, beta or gamma activity can also be chosen to characterize radionuclides as a stressor specific to nuclear power (see Table 2).
During normal operation of NES facilities, only small amounts of radioactive materials are released into the environment, resulting in minor radiological impacts on the general public and the environment, i.e. the regulatory limits are met with high margins [5].

Table 2. Overview of stressors for evaluating nuclear energy system facilities

Stressors	Parameters characterizing stressors	Units	Models
Radionuclides	Total alpha/beta activity in the environments of interest	Bq/m3	Ref. [23]/National models
	Radionuclide activity concentrations in some appropriate media	Bq/m3	Ref. [23]/National models
	Annual effective dose to the population	mSv/a	Ref. [23]/National models
	Doses to reference biota species	mGy/a	ERICA, RESRAD-Biota models [24]
Toxic chemicals	Heavy metals	kg/m3	National models
	Organic compounds	kg/m3	National models
Land commitment	Land temporally committed	m2/tU (or GW(e))	None
	Land permanently committed	m2/tU (or GW(e))	None
Particulates	Concentration of particulates released by facility into the air	g/m3	National models
Heat	Heat rejected by a facility per year	MW(th)/a	National models
Solids	Concentration of solids dissolved in effluents	g/m3	National models
	Concentration solids suspended in water	g/m3	National models

Regulatory standards for chemical stressors

In most countries, there are no regulatory limits (standards) for the emission of toxic chemicals into the environment. On the other hand, in most countries there are limits of toxic substances related to their ambient concentrations. Based on such considerations, environmental authorities of some countries establish reference levels for the emission rates of different chemicals, which are evaluated based on analysis of pollutant dispersion using environment models (computer codes).

Examples of stressors

Table 2 presents the NES stressors, the parameters characterizing the stressors that are limited by regulatory requirements and the available analytical models to calculate the impact of stressors.

Necessary INPUT for an INPRO assessment in the area of environmental impact of stressors

This section defines the necessary input and its sources for assessment of an NES in the INPRO methodology area of environmental impact of stressors.

Specification of the nuclear energy system

A prerequisite for INPRO assessment is the specification of the NES (see the introductory manual of the updated INPRO methodology) to be assessed. The NES is to be defined by the INPRO assessor. For an environmental assessment, in principle, the following aspects should be covered in the specification of the NES:
(a) The complete NES should be considered, covering the entire front end of the fuel cycle, the energy conversion unit (reactor) and the entire back end. For all nuclear facilities, the complete lifetime should be covered, i.e. construction, operation and decommissioning.
(b) A global approach should be used, i.e. no geographical boundaries should be introduced that limit the environmental assessment.
(c) If necessary, environmental burdens may be divided into national (or regional) and those occurring outside the country (or regional) borders if such information would be required by stakeholders.
Thus, by meeting the above defined requirements, the general underlying principle of assessing the entirety of environmental impacts would not be violated.
However, in general, cut-offs, i.e. selection of specific facilities of an NES, will be required in an INPRO assessment. Such an approach is recommended for nuclear technology users and specifically in the case when a State is embarking on a nuclear power programme, i.e. in such a country that the INPRO assessment in the area of environment may consider only the first nuclear power plant and related waste management facilities, assuming that in the later stages of the nuclear power programme, when more experience is accrued in the country, the scope of further INPRO assessments will be expanded.
A nuclear technology developer may focus the environmental assessment (analysis) on the design of the nuclear facility under development.

Information on environmental stressors

An INPRO assessor should have access to relevant design information, i.e. a list of all stressors together with their levels (e.g. emission rates of radionuclides and chemical toxins, size of land use, etc.), of all NES facilities to be assessed. This information should be available in design reports. The assessor should further have access to information on the environmental characteristics of the sites planned for the NES facilities to be assessed. This information should be available from the responsible government organization or utility.
An INPRO assessor should also have access to the same relevant design information of facilities of an existing NES that are comparable to the NES facilities to be assessed. Such facilities are called comparable current facilities in this publication. A comparable current facility means an operating facility of a given type which is located on a site with environmental characteristics that are comparable to the NES facility assessed and licensed according to the requirements comparable to the NES facility assessed. For such a comparable current facility, a complete list of all its stressors and their licensed levels, e.g. emission rates of radionuclides and toxic chemicals, should be available to the INPRO assessor from the potential supplier. The assessor should also have access to important environmental characteristics, e.g. wind pattern, population density, etc., and the regulatory requirements applied for such current facilities. The assessor should further have access to and knowledge of the environmental standards of the country (or region) where the NES is (planned) to be installed. The national standards should be available from the responsible government organization (e.g. via its web site). The same information is needed for the comparable current facilities (if such an approach is planned to be used in the assessment).
The INPRO assessor should also have information to compare the radiotoxicity of release of all radionuclides of the NES assessed with a current NES delivering similar energy products. For the purpose of the INPRO assessment, the total radiotoxicity of an NES is defined through dose conversion factors for collective dose per unit of release, as presented in Ref. [23].
Finally, the INPRO assessor should also have to consider the evidence, e.g. in the form of a written argument to be provided by the potential supplier, to verify that an optimization procedure such as ALARP has been performed during the design of all NES facilities to be assessed.

Other sources of INPUT

The INPRO assessor should contact the government organization responsible for environmental aspects to receive information on the status of EIA studies related to nuclear facilities to be installed in the country as part of the planned NES. If such studies already exist, most of the necessary input for an INPRO assessment should be documented in them.
If a State is embarking on a nuclear power programme and using the IAEA service Integrated Nuclear Infrastructure Review, applying the IAEA milestones approach of Ref. [25], the INPRO assessor should contact the nuclear energy programme implementing organization responsible for this activity to exchange information and assure coordination of this effort with the INPRO assessment.

INPRO basic principle, user requirements and criteria in the area of environmental impact of stressors

This section presents the BP, the URs and the CRs in the INPRO methodology area of environmental impact of stressors.

INPRO basic principle: acceptability of expected adverse environmental effects

INPRO basic principle in the area of environmental impact of stressors: The expected adverse environmental effects of an NES should be well within the performance envelope of current NESs delivering similar energy products.
Adverse environmental effects may arise from any facility and life cycle stage of an NES. Moreover, the design and operation of one facility of an NES can have a major influence on the environmental effects of other facilities. Therefore, in principle, the environmental performance of a proposed NES should be evaluated as an integrated whole (see the footnote in Section 3.1 on the scope of the INPRO assessment in the area of environmental impact of stressors).
The BP expresses an expectation that the environmental performance of the NES assessed will be better than that of a current NES, which is an existing NES comprising facilities of the latest design that is licensed and operating at the time that the INPRO assessment is performed. A current NES may or may not comply with the current standards, depending on whether the current standards are different from those that were applied when the current NES was implemented. However, as further clarified through the first user requirement, UR1, in Section 4.2, the BP requiring that adverse environmental effects of an NES “should be well within” the performance envelope of current NES implies, among others, that the expected adverse environmental effects of an NES assessed should be within the current regulatory standards. Current standards are those prevailing at the time of the INPRO assessment, and are normally met by recently licensed facilities. In some circumstances, it may be appropriate to use an environmental standard that is expected to apply when the NES will be implemented.
Figure 3 provides some clarification of the BP. Each stressor caused either by an NES to be assessed — called an “innovative nuclear energy system” in the figure — or by a current NES chosen for comparison, is represented by a vector whose length is proportional to the level of the stressor, e.g. the release rate of a radioactive nuclide. The radius of the circle passing along the vector represents the environmental standard for that stressor. In this way, each stressor can be represented relative to its standard, and all standards will lie on the circumference (red circle in Fig. 3). The number of stressors illustrated is arbitrary, and the relative magnitude of vectors representing different stressors has no specific meaning.
Stressors arising from the current NES are shown as blue arrows, and their magnitudes (levels) are denoted by L_CNS-i.
The green arrows represent the stressors arising from an (innovative) NES to be assessed, and their magnitudes (levels) are denoted by L_NES-i. The BP assumes that each of the NES environmental stressors must be located inside the red circle (i.e. must meet its standard) representing the current standards.

FIG. 3. Environmental performance envelopes of a current nuclear energy system (blue) and an innovative nuclear energy system (green) to be assessed . CNS — current nuclear energy system; NES — nuclear energy system.

The level of stressors of a current NES may or may not be entirely inside this red circle, depending on whether the current standards are different from those that were applied when the current NES was implemented, as illustrated by L_CNS-4.
As shown in the figure, some stressors arising from an (innovative) NES to be assessed may have a lower magnitude (L_NES-2, L_NES-4, L_NES-5) than the current NES, while some of them may be higher (L_NES-1) or the same (L_NES-6, L_NES-7). In the (innovative) NES to be assessed, some stressors from the current NES may be eliminated (one is illustrated by L_NES-3), while some new stressors (one is illustrated by L_NES-8) may occur. Note that neither the magnitudes of the blue or green areas nor the angles at which the vectors are drawn represent any real quantity, they are for visualization only.
When all stressors are considered, the performance envelope of an (innovative) NES to be assessed (green area) should be within the performance envelope of the current NES (blue area).
In case one (or more than one) of the stressors of the (innovative) NES to be assessed compares unfavourably with the corresponding stressor of the current NES, multivariate analysis might be a possible tool to determine the degree to which the NES to be assessed is within the current NES environmental performance envelope. An alternative approach would be to express the level of all stressors commensurately so that they may be accumulated into a single ‘figure of merit’. Both methods would introduce subjective judgements, but both methods would also be useful for comparisons of one NES to be assessed to another.
When stressor levels, e.g. dose to the population or ambient concentrations of chemicals, are used as part of a comparison between different NESs, it is important to normalize the stressor levels to per unit energy values. Summarizing the statements above, the BP requires that the spectrum of environmental burdens of an (innovative) NES to be assessed remains within the performance envelope of the current NES (see Fig. 3). Thus, operating technology systems will not be substituted by others that are performing worse, but by technologies that tend to reduce environmental damages instead. The INPRO methodology has defined three user requirements UR1, UR2 and UR3 for the BP.

User requirement UR1: controllability of environmental stressors

User requirement UR1: The environmental stressors from each facility of an NES over the complete life cycle should be controllable to levels meeting or below current standards.
As stated previously, any energy system will inevitably introduce stressors to the environment, such as emission of radionuclides or non-radioactive (toxic) chemicals into the air and water, land use and depletion of non-renewable resources, with potentially adverse environmental effects on a local, regional or even global scale. UR1 asks that a designer (supplier) of an NES (or a facility thereof) provides controllability of all stressors throughout the system. Controllability can be achieved by provision of appropriate systems (e.g. filters to reduce emissions) and monitoring equipment (e.g. instrumentation and control equipment to measure release rates) [26, 27]. The operators of proposed nuclear facilities and processes will be responsible for controlling (and documenting) the level of stressors during the lifetime of each facility of the NES.
All stressors of an NES facility should be controllable to levels meeting or below current regulatory standards, i.e. those prevailing at the time the proposed NES is being assessed. In the following, guidance is provided to the INPRO assessor on how to perform an assessment of CRs related to UR1, assuming the INPRO assessor is a nuclear technology user planning to install, in their country, nuclear facilities supplied by a nuclear technology holder.
If an EIA has already been performed for the NES facilities to be assessed and accepted by the authority in the country as part of the site licensing process, CRs related to UR1 should be automatically met, i.e. no further application of the INPRO methodology should be needed; however, the INPRO assessor should review the corresponding reports and confirm that the EIA was performed with due consideration of international guidance documents (e.g. Refs [28, 29]) and agreements (e.g. Refs [11–13]), and document a summary of the results of this EIA in the assessment report.
As a guiding objective for the protection of the environment, theoretically, consideration should be given to the widest possible spectrum of stressors. However, for practical reasons, the degree of inclusion of different stressors in an INPRO assessment has to be limited.
The first step of determining the level of stressors of an NES facility is to produce a list of all relevant stressors. For facilities of the front and back end stages of current NESs, an IAEA publication issued in 1996 presents an overview of major stressors, e.g. heavy metal intrusion into surface water and groundwater from mill tailings and conversion sludge, and mitigation thereof by, for example, effluent treatment [30]. More recent results of the studies, focused on specific details or new technologies, can be found in the proceedings of conferences or scientific publications (see Refs [31, 32]).
In Appendix I, examples are provided to the INPRO assessor on which stressors to focus, in the form of tables that list the important stressors of the facilities of an NES consisting of a water cooled reactor using uranium oxide (UOX) and MOX fuel. Appendix I also presents brief descriptions of the processes in the individual nuclear fuel cycle facilities.
Three types of stressor are covered by UR1 and defined in the tables of Appendix I, namely:

• Exposure of the public from radionuclides released to air and/or water (CR1.1);
• Radiation exposure of biota species (CR1.2);
• Other stressors such as ambient concentrations of toxic chemicals to air and/or water, land use, waste heat rejected, dust, etc. (CR1.3).

The media, i.e. water and/or air, and soil, that the stressors are impacting on are listed in the tables of Appendix I.
Use of a simplified environmental analysis
If an EIA has not yet been performed for the NES facilities to be assessed, it has not yet been accepted by the regulatory authority or the radiation exposure data of the facility assessed are not available, the INPRO assessor is offered an option to continue the environmental evaluation of the NES by trying to perform a simplified (conservative) environmental analysis, as presented in Appendix II, to confirm whether the NES facilities to be assessed will meet national regulatory standards at their planned site.
Use of a comparable current facility
In some particular situations, the simplified environmental analysis may be avoided for the purpose of INPRO assessment, even if the EIA has not yet been completed, assuming that the INPRO assessor considers an NES facility to be based on proven technology. Proven nuclear technology requires that a reference facility — called a comparable current facility — exists that is licensed based on an EIA and that is in operation. The environmental behaviour of such a comparable current facility in comparison to the NES facility to be assessed can be used in the INPRO assessment.
UR1 is satisfied if, in all NES facilities, the levels of all important stressors (listed in Appendix I) are equal or lower than those of comparable current facilities and, additionally, the NES facility satisfies all of the following conditions:

• In the NES facilities assessed, no new stressors should appear.
• The environmental characteristics of the NES facility sites should be comparable to the ones of current comparable facilities.
• Comparable regulatory standards should have been (or will be) applied to both the current facilities and the NES facilities to be assessed.

To confirm the existence of a current comparable facility, the INPRO assessor should compare the environmental characteristics of the planned site of the NES facilities with a site of current facilities. Important environmental characteristics include, for emissions, the stack height of the plant, the hydrological conditions (e.g. release into a river, a lake or the ocean), geology (type of soil, aquifers, etc.), meteorology (e.g. wind patterns), human population distribution around the plant, food chains, endangered species, etc. In principle, all (potential) sites of nuclear installations have different environmental characteristics. However, if important environmental characteristics of different sites are comparable, the levels of stressors of facilities located at different sites can be compared, too. A judgement on the comparability of two sites of nuclear facilities has to be performed by an expert in the area of EIAs.
The INPRO assessor should perform (with support from an expert in environmental analyses) a comparison of the regulatory requirements used for licensing of the current facilities and the ones applicable for the NES facilities to be installed in the country.
If these additional conditions regarding new stressors, comparable environmental characteristics and regulatory standards are not met, then the proposed approach of using the comparison against comparable current facility is not applicable.
UR1 explicitly requires to be applied to each facility of the proposed NES, over its complete life cycle (with the exception of potential accidents and their consequences). The INPRO methodology has defined three CRs for UR1, as presented in Table 1.

Criterion CR1.1: Radiation exposure of the public

ᅠIndicator IN1.1: Dose to the publicᅠ

Dose to a representative person is considered as IN1.1. Depending on the status of the assessed NES deployment, this information may be directly available from the design or licensing documents of the NES to be assessed. If these data cannot be found, a simplified environmental analysis (see Section II.2) should be performed by the assessor. Alternatively, a comparison with a current comparable facility (when applicable) can be used, as described earlier.

ᅠAcceptance limit AL1.1 for dose to the publicᅠ

Based on GSR Part 3 [2], regulatory authorities should define dose constraints as outlined in detail in IAEA Safety Standards Series No. WS-G-2.3, Regulatory Control of Radioactive Discharges to the Environment [33]. A dose constraint should be set up by the regulatory authority for a single facility on a given site, taking into account local conditions that are relevant for radiological impact on humans. More details on dose constraints are given in Section II.2.3. The INPRO methodology recommends using dose constraints established by a national regulatory body for an NES facility as an AL for the assessment of radiation exposure of the public. For the cases when dose constraints are not defined by a national regulatory body, the INPRO methodology recommends using the following values as ALs, which represent minimum constraints for a single source (facility) used in current practices by different Member States: Limit of 0.08 mSv/a for nuclear power reactors; Limit of 0.2 mSv/a for all other nuclear facilities of the NES assessed. Use of a current comparable facility For the case of an INPRO assessment of CR1.1 by comparison of stressors from NES facilities assessed against stressors from comparable current facilities, as described earlier in Section 4.2, the INPRO methodology proposes to use the licensed levels of stressors (also called reference levels) of a selected comparable current facility as AL1.1 for the NES facility to be assessed. This means, for radioactive discharges of an NES facility to be assessed, that licensed levels of stressors of a current comparable nuclear facility licensed in the country of its location by the responsible regulatory authority can be used as AL1.1 for the NES facility assessed. This proposed approach is only applicable if, for both the comparable current facility and the facility to be assessed, the environmental characteristics of the plant and the site and the regulatory environmental requirements are sufficiently similar. A sufficient similarity is necessary because, in particular, the licensed levels of stressors of a nuclear facility depend on the environmental characteristics of its site and the applicable regulatory standards. Additionally, the NES facility to be assessed should not show a higher level of a stressor and no additional stressor in comparison to the current facility. Thus, the INPRO assessor should check whether there are any new stressors or higher levels of stressors in the assessed NES facilities that do not occur in current facilities. However, in an NES facility of proven technology (usually offered by a technology holder to a technology user), no new or higher levels of stressors are expected in comparison to a current facility.

Criterion CR1.2: Radiation exposure of non-human species

ᅠIndicator IN1.2: Doses to the reference biota speciesᅠ

Current international trends in radiation protection show an increasing awareness of the vulnerability of the environment. These trends also indicate the need to be able to demonstrate (rather than to assume) that the environment is protected against the effects of industrial pollutants, including radionuclides, in a wider range of environmental situations, irrespective of any human connection. The system of protection and safety required by GSR Part 3 [2] provides a basis for protection from the harmful effects of radiation of both the public and the environment. This procedure is usually accomplished by means of an environmental assessment that identifies the target(s), defines the appropriate criteria for protection and assesses the impacts on biota. Methods and criteria for such assessments are being developed and will continue to evolve. The 2007 recommendations of the International Commission on Radiological Protection (ICRP) [34] effectively extended the system of protection to address protection of the environment, including flora and fauna, more explicitly. These recommendations explore the objectives of environmental protection and explain the basis for the proposed reference animals and plants (RAP), which is a small set of hypothetical entities that are representative of animals and plants present in different environments (terrestrial, freshwater and marine) and which form the basis of a structured approach to the assessment of exposures to, and effects of, ionizing radiation [35–37]. Therefore, doses to the reference organisms are considered as IN1.2. These doses can be estimated by the assessor using a simplified approach, as presented in Section II.3, when necessary.

ᅠAcceptance limit AL1.2 for doses to the reference biota speciesᅠ

In the scientific annexes to the 1996 and 2008 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) reports [38, 39], published data on the exposures and effects on non-human biota have been evaluated. It has been found that “chronic dose rates of less than 100 μGy·h−1 (2.4 mGy·d−1) to the most highly exposed individuals would be unlikely to have significant effects on most terrestrial communities” and “that maximum dose rates of 400 μGy·h−1 (10 mGy·d−1) to a small proportion of the individuals in aquatic populations of organisms would not have any detrimental effects at the population level”. These values are in agreement with those reported elsewhere [40, 41], and reflect an international consensus on doses which could be considered as acceptable for biota species. The ICRP defined a set of dose reference values (derived consideration reference levels, DCRLs) that are specific to each of the different RAPs [35]. A DCRL can be considered as a band of dose rates, spanning one order of magnitude, within which there is some chance of causing deleterious effects in individuals of a given RAP category arising from exposure to ionizing radiation. The presented data demonstrate that no radiation effects or very low probability effects can be observed for aquatic and terrestrial species at the level of 0.1–1.0 mGy/d. Noting the similarity of these data, the level of 1.0 mGy/d can be used as an AL for non-human biota. Based on the data on projected ambient concentrations of main dose forming radionuclides in the major environmental compartments such as air, soil and water, the INPRO assessor should perform (with support from an expert in environmental analyses) assessments of the doses to the RAPs. Methods and models for such assessments are freely available, and can be downloaded from appropriate web sites (see Section II.3). The IAEA model [23] presented in Section II.2 can be used for calculation of the ambient concentrations of radionuclides, if these data are unavailable at the time of assessments. Alternatively, a comparison of stressors from the NES facilities assessed against stressors from current facilities (when applicable) can be used, as described earlier.

Criterion CR1.3: Impacts of chemicals and other non-radiation environmental stressors

ᅠIndicator IN1.3: Levels of chemicals and other stressorsᅠ

Radiological impacts in a particular environment constitute only one type of impact, and, in most cases, may not be the dominant impact of a particular facility or activity. Furthermore, the assessment of impacts on the environment needs to be viewed in an integrated manner with other features of the protection and safety system in order to establish the requirements applicable to a particular source. As there are complex interrelations, the approach to the protection of people and the environment is not limited to the prevention of radiological effects on humans and on other species. An integrated perspective has to be adopted to ensure the sustainability, now and in the future, of agriculture, forestry, fisheries and tourism, and of the use of natural resources. Levels of the chemical stressors (e.g. concentrations at the receiving environment and/or doses) which can be released from every facility of a given NES are to be defined according to the national regulatory requirements. The (normalized) level of the stressor land use is to be defined in m2 per throughput (tU) of the facility or electricity generated in a year (GW·a) and/or in a shorter period such as a day. Waste heat rejected (from the power plant) to air and/or water is to be defined in energy released to the media (MW·h) per electricity generated by the NES in a year (GW·a) and/or in a shorter period.

ᅠAcceptance limit AL1.3 for levels of chemicals and other stressorsᅠ

For toxic chemicals, the national licensing requirements should be used as AL1.3. For the other stressors listed in Appendix I, national licensing requirements, e.g. the (normalized) amount of heat rejected to the ultimate heat sink such as a river or ocean, should be used as AL1.3. Alternatively, a comparison of chemical and other stressors from NES facilities assessed against stressors from comparable current facilities (when applicable) can be used, as described earlier.

Final assessment of UR1: Controllability of environmental stressors

The tables in Appendix I can be used by the INPRO assessor to check whether all important stressors of NES facilities have been considered by the designer.
The acceptance limits AL1.1–AL1.3 of CR1.1–CR1.3 are met if, in all NES facilities, the levels of all important stressors (listed in Appendix I) are in compliance with existing national or international standards.

User requirement UR2: reduction of total environmental impact of emitted radioactivity

User requirement UR2: Total radiotoxicity of radionuclides discharged by the NES assessed should be lower than that of a current NES delivering similar energy products.
Radiation tends to be considered as a stressor that is specific to nuclear power, and the concerns of the ecological safety of the nuclear industry are frequently related to the release of radionuclides into the environment. As different radionuclides released by nuclear facilities, including waste management facilities, differ in terms of producing detrimental health or environmental effects, the INPRO methodology suggests using the concept of radiotoxicity to balance the effects of different radionuclides and to combine them in a single integral parameter. In its simplest interpretation, radiotoxicity can be defined as the ability of incorporated radionuclides to cause harmful health effects [42]. This simple definition gives a clear understanding of the basic approach; however, it cannot be directly applied to the emitted radioactivity, as it does not consider the transport of radionuclides between the emitter and receptors.
In order to take into account environmental pathways, the INPRO approach is based on application of dose conversion factors for collective dose per unit activity discharged. The approach considers the discharge of radionuclides into the atmosphere, freshwater bodies and marine water, thus covering some differences in locations of nuclear facilities. Hence, radiotoxicity is defined in this publication as an activity of a radionuclide in a release multiplied by a parameter reflecting a measure of hazard from a given radionuclide.
Although the dose conversion factors (or collective effective dose commitments per unit activity discharged) are lump parameters, they are based on comprehensive calculations where many environmental transfer parameters and reference input data for such assessments are included. In particular, the data provided in Ref. [23] are given for both a simple generic model, which can be used to estimate collective doses for the transfer of radionuclides in the environment originally developed by UNSCEAR [43], and more complex models, which consider some site specific factors. To provide comparable bases for assessment of new NESs, generic global parameter values are used with these models.
For atmospheric releases, three exposure pathways are considered: inhalation, ingestion of terrestrial foods and external radiation from deposited material. A population density is required in this calculation of collective dose; for the purposes of calculating screening values, a population density of 35 people per km2 is used [23]. This represents a global average; considerably higher densities can be found in some countries, while lower densities can be found in others. The foods considered are: grains, green vegetables and fruit, root vegetables, milk and meat. Global average yields of particular foods are also required and are taken from the compilation of the Food and Agriculture Organization of the United Nations (FAO). These are the collective effective dose commitment values calculated using the effective dose coefficients given in Ref. [23]. In most cases, the values are of the same order as, or in the range of, the collective doses obtained from the more complex models, and are also presented in annex VII of Ref. [23].
For releases of radionuclides in liquid form, their dispersion and subsequent transfer to humans will vary considerably depending on the characteristics of the receiving water body. Although, the general model is used, account is also taken of the transfer of radionuclides to sediments through the use of the sediment distribution coefficient K_d. The exposure pathways considered are the consumption of drinking water and aquatic foods.
UR2 explicitly requires to be applied to each facility of the proposed NES, over its complete life cycle, and to consider the total environmental impact from discharged radioactivity.
The INPRO methodology has defined one CR for UR2, which is presented in Table 1.

Criterion CR2.1: Reduction of environmental impact of radiation

ᅠIndicator IN2.1: Total radiotoxicity of radionuclides emitted to the environment from the nuclear energy system assessedᅠ

For the purposes of the INPRO assessments, the radiotoxicity Rki,j is defined as the integral activity (Ai,j, in units of Bq) of radionuclide (i) discharged per GW∙a for each type of release (j) from a given facility (k) multiplied by the corresponding dose conversion factor for collective dose (DCFi,j , in man Sv/Bq), as given in Ref. [23]: $R_{i,j}^{k}=A_{i,j}^{k}\times {DCF}_{i,j}^{k}$; (1) It must be realized that the concept and product of the radiotoxicity assessment used in UR2 (CR2.1) are different from those required in UR1 (CR1.1). Annual effective dose is used for assessment of the compliance with radiation safety standards for the public exposure (UR1). Dose conversion factors for the collective effective dose commitment used for assessments of radiotoxicity are integrated to infinity, providing an IN of the total impact of the discharge of radionuclides to the environment within UR2. Index j corresponds to the discharge of radionuclides from the facility k to the air, freshwater and marine waters, respectively. Then, the radiotoxicity of the release of any facility k is given by: $R^{k}=\sum _{1}^{3}\sum _{1}^{N_{j}}R_{i,j}^{k}$; (2) where Nj is the number of radionuclides released to environment j. Then, the total radiotoxicity of the release from the proposed NES (RT) can be calculated by: $R^{T}=\sum _{1}^{M}R^{k}$; (3) where M is the number of nuclear facilities that constitute the NES. If only one new facility (e.g. a new nuclear power plant) is added to an existing NES, the comparison of radiotoxicity should be done only between newly introduced and former elements of the NESs, as the radiotoxicity of the remainder of the NES remains the same. The collective dose conversion factors given in Ref. [23] were obtained using the effective dose coefficients for calculation of the effective doses suggested in Ref. [23] for screening purposes. The advantage of such an approach is that the parameters for simplified dose analysis recommended by UR1 are based on the same data as for UR2 and do not require the use of input other than from Ref. [23]. Another general advantage of this approach is the possibility of explicit summing of the radiotoxicity values calculated for different components of the NES, which could enable direct comparisons of NESs.

ᅠAcceptance limit AL2.1 for total radiotoxicity of radionuclides emitted to the environment from the nuclear energy system assessedᅠ

Total radiotoxicity is an integral parameter, and should be calculated based on the releases of all facilities constituting the NES, i.e. environmental analysis should be performed at the whole NES level. The acceptance limit AL2.1 of CR2.1 is met if the total radiotoxicity evaluated for the proposed NES is lower than that of any current NES which provides the same energy products. In the case of a positive INPRO assessment of CR1.1 by using the method of comparison of stressors from comparable current facilities against stressors from NES facilities assessed (given that all necessary conditions are fulfilled, as described earlier in Section 4.2), CR2.1 will be fulfilled automatically.

User requirement UR3: optimization of the measures to reduce environmental impact

After confirming that UR1 and UR2 are fulfilled, the next step of an INPRO assessment is to check whether the NES facility design has been adjusted by the designer (supplier) to provide optimized protection of the environment.
GSR Part 3 [2] is based on the ten fundamental safety principles stated in IAEA Safety Standards Series No. SF-1, Fundamental Safety Principles [44]. Fundamental Safety Principle No. 5 of SF-1 [44] requires optimization of protection and states that “Protection must be optimized to provide the highest level of safety that can reasonably be achieved.” More specifically, para. 3.24 of GSR Part 3 [2] requires:

“For occupational exposure and public exposure*, registrants and licensees shall ensure that all relevant

factors are taken into account in a coherent way in the optimization of protection and safety to contribute to achieving the following objectives:
(a) To determine measures for protection and safety that are optimized for the prevailing circumstances, with account taken of the available options for protection and safety as well as the nature, likelihood and magnitude of exposures;
(b) To establish criteria, on the basis of the results of the optimization, for the restriction of the likelihood and magnitudes of exposures by means of measures for preventing accidents and for mitigating the consequences of those that do occur.”

---

“* Requirements for the optimization of medical exposure are specified in paras 3.162–3.177.”

Therefore, the INPRO methodology UR3 in the area of environmental stressors reads as follows.

User requirement UR3: The measures applied to reduce adverse environmental impact attributable to an NES should be optimized.
It is suggested that the principle of pollution prevention [45] should be applied for this purpose by the designer, i.e. reduction of the amount and level of the stressor produced in the NES is the most favoured means of reducing potential environmental impacts.
As stated in Section 4.1, the NES to be assessed should be held to higher environmental standards than a current NES. Therefore, UR3:

• Applies the philosophy of achieving the best environmental performance reasonably practicable for an NES facility to be assessed;
• Covers all adverse environmental effects, not only the radiological effects on humans;
• Continues to recognize that costs incurred to enhance environmental performance should not be greatly disproportionate to the achieved benefit.

The INPRO methodology has defined one CR for UR3, which is presented in Table 1.

Criterion CR3.1: Optimization of the measures to reduce environmental impact

ᅠIndicator IN3.1: Measures to reduce environmental impact of the nuclear energy systemᅠ

There are several options available to the INPRO assessor on how to confirm whether the measures to decrease the environmental impact of stressors of an NES facility are optimized. This INPRO Manual is not intended to provide any specific recommendations or indicate preferences on which optimization concept and approach should be used for such a purpose, and relies instead on regional or national expertise in this area. Possible options demonstrating optimization of the measures decreasing environmental impact are the BATs, the BEP or the best available technology not entailing excessive costs (BATNEEC) concepts. Other techniques such as the ALARA or ALARP concepts can also be used by the designer of an NES facility to demonstrate that measures to provide a reduction of the environmental impacts are optimized depending on the requirements of national regulations and experience. The application of the BAT and the BEP concepts to optimizing the environmental impact of nuclear facilities has been promoted by the commitments related to the limitation of environmental impact from the nuclear sector. Within the Convention for the Protection of the Marine Environment of the North-East Atlantic [13], contracting parties are requested to apply these concepts, where appropriate, to prevent and minimize contamination of the marine environment. Similar statements have been made by the EU directive on industrial emissions [46]. BAT means the preferred technique for a particular activity, selected from among others after taking into account several factors. Thus, the BAT is not a specific level of treatment, but is the conclusion of a selection process in which several alternatives are evaluated. The BAT selection process means the evaluation of candidate alternative techniques in order to select the BAT after considering: technology; economics; age of equipment and facilities involved; processes employed; engineering aspects of the application of various types of control technique; process changes; other environmental impacts (including energy requirements); safety considerations; and policy considerations. Overall, the BAT may be explained as follows [46]: ‘Best’, in relation to techniques, means the most effective technique in achieving a high general level of protection of the environment as a whole; ‘Available’, meaning those techniques developed on a scale that allows implementation in the relevant class of activity under economically and technically viable conditions, taking into consideration the costs and advantages, whether or not the techniques are used or produced within the State, as long as they are reasonably accessible to the person carrying out the activity; ‘Techniques’, including the technology used and the way in which the installation is designed, built, managed, maintained, operated and decommissioned. The relationship and differences between the BEP and BATNEEC concepts can be summarized as follows [47]. BATNEEC is construed to mean the provision and proper maintenance, operation, use and supervision of facilities which are the most suitable for the purposes. The manner in which this is to be achieved is wide ranging, but with the overall objective that BATNEEC will be used to limit, abate or reduce an emission from an activity. The focus is on defined activities, though also addressing areas such as treatment of waste. BEP is more comprehensive, addressing the entire product life cycle through a combination of practices. These practices may involve producers, importers, distributors, commercial users and the general public, as well as those engaged in the collection, recovery or disposal of the substance when it enters the waste stream [47]. Detailed introductory information on the BAT and BEP methods and an example of application are provided in Section III.2. ALARA is an approach used for radiation protection to manage and control exposures (both individual and collective to the work force and to the general public) and releases of radioactive material to the environment so that the levels are as low as reasonable, taking into account social, technical, economic, practical and public policy considerations. The ALARA concept was first described in an ICRP publication in 1973 [48]. Updates have been given by the ICRP in 1977 [49] and in 2006 [50]. In the latest report, the ICRP focuses more on expanding the optimization process, reflecting the increased role of individual equity, safety culture, stakeholder involvement in addressing receptor scenarios, site specific evaluation of exposure, intergenerational equity and many other aspects. The ICRP reports provide a comprehensive list of factors that should be considered for optimization. Although there is limited guidance on how to apply ALARA principles to the performance assessment process, the ALARA process is described in some regulating documents, such as the United States Nuclear Regulatory Commission (NRC) regulation 10 CFR 20 [51]. The definitions usually indicate that exposures should be controlled so that releases of radioactive material to the environment are as low as reasonable, taking into account social, technical, economic, practical and public policy considerations. It is also noted that ALARA does not imply a certain dose limit or dose constraint, but that ALARA is a process which has the objective of attaining doses as far below the applicable limit of this part as is reasonably achievable. The ALARP concept states that a risk has be reduced to a level that is “as low as reasonably practicable, social and economic factors taken into account”. It is a general concept for risk reduction applied in several countries, including Canada and the United Kingdom (e.g. [52–54]). Other Member States do not use ALARP on a regular basis; instead, standards and good engineering practices are adhered to, and legislation tends to require absolute levels of safety. The term ALARA is used interchangeably with ALARP in the United States of America, almost exclusively in the field of radiation protection. The ALARA principle is conceptually similar to ALARP, but does not involve a region of broad acceptability. An example describing application of the ALARP concept is given below and detailed in Appendix III. The basic approach using the ALARP concept is that the NES is designed according to modern engineering principles. Then, the design should be reviewed to verify that the risk to the environment is ALARP. The ALARP technique includes an evaluation of both the cost and benefit of reducing the level of significant environmental stressors. The evaluation should lead to either a reduction of stressors or rejection of a possible reduction on the grounds that the cost of the reduction would significantly outweigh the benefit. This evaluation has to be performed by the designer (supplier), and the results of that process should be available to the INPRO assessor.

ᅠAcceptance limit AL3.1 for optimization of the measures to reduce environmental impactᅠ
The acceptance limit AL3.1 of CR3.1 is met if evidence is available to the INPRO assessor that at least one of the possible optimization approaches was duly applied by the designer of the NES facility assessed.

Appendix III

BASIC CONCEPTS FOR OPTIMIZING MANAGEMENT OPTIONS FOR REDUCTION OF ENVIRONMENTAL IMPACT

As low as reasonably practicable

Concept

The concept of ALARP (economic and social factors taken into account) is used to define an AL for several INs in different areas of the INPRO methodology, especially for the environment and waste management.

FIG. 5. The ALARP concept [21].

The concept is illustrated in Fig. 5. As shown, the risk (symbolized by the triangle) is divided into three regions: a broadly acceptable region, a tolerable region where a process for ALARP has to be used and an unacceptable region.
As a first step of the ALARP concept to be applied within the INPRO methodology, the boundary values of these three regions have to be determined: the boundary between the tolerable and the unacceptable regions, usually called a basic limit (BL); and the boundary between the tolerable and broadly acceptable regions, sometimes called a basic objective (BO). The next step is to confirm that the value of the indicator of an NES is within the ALARP region that is below the BL. The last step is to confirm that in an optimization analysis, all measures to reduce the specific risk have been taken into account by the designer up to a level where the costs for these measures would have become ‘grossly disproportional’ to the benefit gained. It is important to note that, in the case when the indicator of an NES has a value in the broadly acceptable region below the boundary BO, no further effort is necessary to fulfil the ALARP concept.
BL and BO values may be specified for specific indicators in national regulations or as an outcome of an EIA, or it may be necessary to infer such values from other evidence such as: licence conditions; actions planned, under way or completed to remediate an existing situation or improve a given practice; presentations at national or international conferences; publications in peer reviewed journals, the IAEA Safety Standards Series and other IAEA publications; and the work of other organizations such as the ICRP, the NEA and the European Commission. When a BL or a BO is deduced from such evidence, the rationale for doing so needs to be clearly stated to ensure transparency. While national and international consensus may not exist and may be slow to emerge, suggesting a value for a BO and the associated rationale would be expected to make a valuable contribution to the process of national and international consensus building.

Application of the ALARP concept by a technology developer

The flow chart in Fig. 6 exemplifies the procedure that a technology developer (designer) could follow to confirm compliance of an NES under development with the INPRO methodology CR3.1 in the area of environmental stressors (optimization of the measures to reduce environmental impact).
The quantity, optimized in an ALARP analysis, could be an individual stressor level, a weighted combination of stressor levels (e.g. estimated dose) or some other risk related function of the system parameters. The values of BL and BO are to be set on the basis of expert judgement, best technology available, regulatory clearance levels or other information.
The depth that the ALARP analysis can reach depends on the maturity level of the NES assessed. For early designs that are still at the conceptual stage, the optimization process could be guided by establishing a figure of merit for acceptable limits and restrict the ALARP procedure to stressors (radioactive as well as non-radioactive, if relevant) that have been identified as being the most significant or of the highest priority. Further reductions of the number of stressors could be accepted only if they have been appropriately justified by the designer, with evidence provided in the analysis report.
The ALARP concept might be applied to the whole NES under development, for which adequate BL/BO values would need to be defined. In the case when the optimization occurs both at the individual facility (component) level and at the whole system level, care needs to be taken to ensure that double counting does not occur. As an example, in addition to a BL and a BO on ¹⁴C emitted from a reactor or a reprocessing facility, a BL and BO for the aggregated ¹⁴C from the entire NES under development, including reprocessing and waste treatment facilities, can also be set (see also the discussion below on the reduction of collective doses).
In the following, the proposed approach for each facility (component) is described in more detail, as it corresponds to the way that ALARP is mostly applied in current practices.
If the analysis is performed in several stages for addressing successive levels of maturity of the NES being developed or for considering possible changes in the regulations of the Member State or in international standards, the BL and BO values might also need to be redefined, and the ALARP analysis may become more refined and complex.
If the NES being developed is just at its conceptual stage, the ALARP demonstration may be reduced to a discussion or a series of statements (illustrations) aimed at showing that modifications to the system that could reduce these stressors have been considered, and that these stressors cannot practicably be reduced further. At the very least, the developer (designer) should acquire evidence that sufficient thought has gone into evaluating the potential of adjustments in the NES facilities and processes to reduce environmental effects. The descriptive demonstration, adequately reported in the analysis report, should be finalized in the following phases of design development. Reference [72] explains that the requirement for risks to be ALARP “is a requirement to take all measures to reduce risk where doing so is reasonable. In most cases this is not done through an explicit comparison of costs and benefits, but rather by applying established relevant good practice and standards.”
Hence, it is expected that if an analysis of more refined stages of the design process is performed, this should verify ALARP for the same component(s)/stressor(s), and, if the design is changed, track the reasons for technical modifications in relation to the previous ALARP analysis.

FIG. 6. Proposed method for ALARP applied in sequence to all facilities (components) of a nuclear energy system (NES) or, if necessary, to groups of facilities or/and to the whole NES [1]. ALARP — as low as reasonably practicable; BL — basic limit; BO — basic objective; RD&D — research, development and demonstration.

If a facility, or the whole NES, is at a more advanced state of development, ALARP may require the application of tools for aiding in decisions such as CBA or MCDA [72, 118]. It may happen that ALARP implementation in a given facility may be challenging (stressors must be below BL for licensing) because of compensating effects across the spectrum of stressors of the facility itself or group of facilities of the NES. Reference [72] notes that “where there are several risks which interact, whether arising from a single hazard or from different connected hazards, there may be a need for balancing to achieve the best overall solution.” In this case, the developer (designer) should demonstrate and document that ALARP is fulfilled at a higher level by analysing groups of components or the NES as a whole (see Fig. 6). A sensitivity analysis may be useful to show the robustness of the adopted technical solution by varying key parameters (see the discussion below on the proportion factor between costs and risks). CBA and/or MCDA need to be applied considering all aspects within the boundary of the assessment.
With reference to Fig. 6, what ‘gross disproportion between costs and risk reduction’ means for application, no algorithm has been defined by the risk and safety authorities adopting ALARP, rather only a general guidance for judgement to allow flexibility on a case by case basis. For current technology, ALARP involves consideration of good practices [52]. However, this may change owing to innovation, which is improving the degree of control, cost changes or knowledge about hazards [72]. For new technologies in an NES, evolving good practices could be followed to start with, and then consideration given to whether there are alternative processes or procedures that could be performed to reduce the risk on the basis of first principles to compare the risk with the sacrifice involved in further reducing it. In many instances, such ‘first principles’ comparisons can be carried out qualitatively, i.e. using common sense or exercising professional judgement or experience [52]. In the case when the costs are definitively very high and the reduction in risk is just marginal, then ALARP is likely demonstrated, and no further improvements need to be designed or implemented. Conversely, in most cases where the improvements identified are simple or cheap to implement and the risk significantly reduced, these improvements are required, and ALARP can be considered to be achieved without further analysis [52].
For less clear cut situations, which are most likely for innovative technologies, a more formal CBA may provide additional insight to help to arrive at a judgement. In a CBA, both risk and sacrifice are converted into monetary terms. In a standard CBA, the rule applies that the measure should be adopted if benefits outweigh costs. However, in ALARP judgements, the measure has to be adopted unless the sacrifice is grossly disproportionate to the risk. Therefore, “the costs can outweigh benefits and the measure could still be reasonably practicable to introduce. How much costs can outweigh benefits before being judged grossly disproportionate depends on factors such as how big the risk is to begin with (the larger the risk, the greater can be the disproportion between the cost and risk)” [52].
Although individual doses to members of the critical groups are used for establishment of standards, hence of BL and BO values, for the CBA, the total social costs of all emissions (radiological as well as non-radiological) have to be taken into account. Therefore, it is the collective dose (see Appendix IV) that should be used. The scope of the analysis depends on the choice by the developer (designer) of the consistency within the analysis. Ideally, externalities should be evaluated considering the LCA of the entire cycle, thus including secondary burdens from flows of material and energy into the system. However, in the case when the options to be addressed in the ALARP procedure would not meaningfully change the secondary contributions in relative terms, the analysis can be restricted to the effect of primary (or direct) burdens only. Studies of external costs for current nuclear technologies can be found in Refs [110, 115, 119, 120].
The ALARP process should also take into account risks that may affect future generations, as they may stem from radioactive waste management and decommissioning. Reference [72] notes that “risks should be assessed in a holistic manner and not restricted to part of the overall time period or part of a process.” Further elaboration points out that: “Although it could be argued that the next few generations may gain some indirect benefit, the uncertainty of how they will view the risks left to them (and indeed the uncertainty of any benefits further into the future) argues for a precautionary approach and hence a particularly stringent demonstration that risks are indeed ALARP.” Considering that the demonstration of long term sustainability for an NES is the ultimate objective of an INPRO assessment, the requirement of consideration of effects into the future should be even stronger when applied to an NES under development.
The following information, although referring to the ALARA approach, may also be of interest for ALARP. The DOE recommends that for the purpose of comparing ALARA alternatives for operational systems, the lifetime of the facility generally is a basis for truncating collective dose estimates, temporally [118]. However, where cleanup, restoration and waste management activities are necessary, the time frame for the analysis can be much longer. In particular, for long lived radionuclides, integration times may be determined by the uncertainties in scenarios and by the physical parameters affecting dose rates. The DOE states that, typically, it is only appropriate to conduct quantitative comparisons for a few hundred years or less. Although evaluating doses for periods of up to a thousand years may provide useful information, periods beyond this length of time should not be used in quantitative ALARA assessments [118]. However, although this position may be adopted for an analysis, provided it is justified by the nature and amounts of the releases, consideration of longer integration times may be useful in other parts of the analysis.
Reference [72] defines that: “The safety benefit of the improvement is the incremental difference in risk between the two estimates in terms of the detriments (i.e. all the adverse consequences) and their likelihoods, summed over the remaining life of the facility.” This includes detriments from normal operation such as radiation exposures of workers and the public; detriments from accidents which again includes radiation exposures to the public and workers but also includes other detriments such as the need to decontaminate areas, evacuation, relocation and food restrictions. Valuation of detriments is a subject of much discussion and research [72]. The UK HSE [71] uses £1.5 million (2009) for the value of preventing a statistical fatality. In the case of death caused by cancer, the HSE takes the view that people are prepared to pay a premium. Thus, a higher value, such as twice that defined above, should be used. It is suggested that this higher value is also appropriate for all radiation deaths.
In the European study ExternE [109, 120], the value for average social (or external) costs in Europe attributed to any cancer, whatever its origin and outcome (fatal or non-fatal), is €2 million. In the case where an assessment is performed for a different country, if ‘willingness to pay’ (WTP) estimates are lacking, values established in Europe or the United States of America can be adjusted to specific conditions using the ratio of the purchasing power parity gross national product per capita. The adjustments are based on the assumption that there is an ‘elasticity’ of WTP with respect to real income. An example of the application of this approach to the assessment of electricity scenarios (including nuclear) for the Shandong Province, in China, can be found in Ref. [121]. Use of external cost calculations implies verification, to the latest available information on damage functions and external costs in publications, and detailed reporting on the assumptions/options used or possible modifications/adaptations.
The following applies to ALARA as implemented in the United States of America. However, the information may also be useful for ALARP assessments. For the costs associated with units of doses, the linear relationship of health effects with dose is postulated, thus making the monetary value independent of the magnitude of individual doses. Several rationales have been adopted for the estimation of the monetary value of a unit of collective dose or other effects of non-radioactive substances, which can be found in the literature. The use of WTP, i.e. the willingness to commit resources to avoid the negative impact, is considered here. As an example of application, in 1995, the NRC [122] re-evaluated the monetary equivalent value and issued regulatory analysis guidelines that recommend US $2000/man rem (US $200 000/Sv) as the current monetary equivalent value for converting collective dose to US dollars [118]. The DOE accepted the NRC recommendation, and, because of the uncertainty in the values used in ALARA analyses, further elaborated that detailed ALARA evaluations use the range for comparing alternatives. The DOE evaluations to support ALARA analyses apply monetary equivalents for a man rem in the range US $1000–6000 with a nominal value of US $2000 [118, 123]. Assuming that one man rem corresponds to a potential risk of 5 × 10⁻⁴ radiation induced fatal health effects (generally cancers) for the population, the range recommended by the DOE would correspond to a range of US $2 million to US $12 million per hypothetical radiation induced cancer death averted [118].
In cases where, in addition to health (and environmental) risks and costs of measures to reduce them, several other non-health detriments are identified, these should also be included in the analysis with societal costs when appropriate and feasible. These effects can be physical (e.g. waste heat discharge, noise or damage from potential, very low frequency/high consequence accidents — for the latter, see Ref. [120]) or sociopolitical (e.g. aversion, opposition or proliferation). Some may be quantified in monetary terms and could be included in the CBA. However, in most cases, such quantification has strong subjective elements, i.e. weighting factors may intervene (see discussion in Ref. [118], p. 18). Therefore, in cases where non-monetary aspects are identified or anticipated as a crucial part of the decision on which measures identified in an ALARP process should be implemented, a formal MCDA may be best applied.
As mentioned in Ref. [72], if the risks (given by frequency multiplied by the consequences) are high, then the demonstration of ALARP should be more rigorous than if the risk is low. Where risks are high, the consequences should be weighted more than the frequency, and the ALARP demonstration should be accurate. The technical assessment guide of the Office for Nuclear Regulation [72] provides specific guidance for inspectors of nuclear installations on what they should expect of a licensee in meeting legal requirements to reduce risks to ALARP. It suggests, on the basis of previous experience, a disproportion factor between costs and risk reduction benefits of up to three for workers, whereas for risks to the public, the factor would depend on the level of risk, suggesting a factor of about two for low risks and about ten for higher risks. These factors may be applied in an analysis, unless other rationale are provided.
Owing to the uncertainties at various levels in the system under scrutiny and in the methods used for the prediction of releases and associated consequences, it is suggested in Ref. [72] to base the judgement on the appropriateness of the proportion factor on the robustness of the analysis. This factor should also be one of the parameters to be varied in a sensitivity analysis
. Considering that, usually, the scope of an environmental analysis includes also anticipated operational occurrences, it is useful that the National Radiological Protection Board (NRPB) has produced guidance relating to the dose saved resulting from routine exposure or minor incidents, i.e. stochastic effects, up to about 100 mSv. The NRPB recommends that an increasing multiplier is used in ALARP demonstrations as the dose increases, and also recommends the HSE Nuclear Safety Directorate to assess licensees’ submissions using this approach. Reference [72] suggests that a factor (for costs outweighing risks) of less than ten in the vicinity of the intolerable region is unlikely to be acceptable and, for hazards that can cause large consequences, the factor may need to be larger still. This requirement may be understood as being even more pronounced for an NES under development, especially at the early design stages for which the uncertainties may be predominant on the cost differences calculated for risk reduction measures. The recommendation of Ref. [72], discussed above, to include the proportion factor within the parameters to be varied in a sensitivity analysis is repeated here.

Example of application to a reprocessing facility

One of the rather few examples of the application of ALARP to a facility of a current NES [84] reports on the Environment Agency’s re-examination of the Sellafield reprocessing plant’s radioactive discharge authorizations from 2000 to 2002. This example would have the potential to also serve for assessing the ALARP concept of future reprocessing plants. However, the information available in Ref. [84] is rather limited, and is therefore insufficient for full understanding of the procedure used (e.g. missing information on risk levels before implementation of ALARP, how the optimized actions were justified and on the costs involved).
Table 19 presents the doses to the critical groups caused by radioactive discharges from the Sellafield reprocessing plant in 2001 [84].

Table 19. Critical group doses from 2001 discharges from the sellafield site [84]

Aerial effluent discharges		Liquid effluent discharges
Radionuiclide	Critical group dose (adult) (μSv)	Radionuclide	Critical group dose (seafood consumer) (μSv)
Ar-41	31	Tc-99	23
Sr-90	11	C-14	5
Ru-106	3	Cs-137	4
Cs-137	3	Ru-106	2
Pu alpha	2	Sr-90	1
C-14	1	Co-60	1
Kr-85	1	Others	1
I-129	1
Am-241	1	Am-241*	50
I-131	1	Pu alpha*	28
Others	3	Pu-241*	4
Total	58	Total	119

* - Historic contribution from discharges prior to the Site IonExchange Effluent Plant (SIXEP) and the Enhanced Actinide Removal Plant (EARP) have been introduced. The strategy of the operator, British Nuclear Fuels (BNFL), for controlling radioactive discharges from the Sellafield site consists of:
(a) Designing plants to minimize radioactive arisings, and subsequent discharges and disposals, where practicable by:

• Employing processes that avoid the production of gaseous and liquid by-products, and that avoid solid waste generation (it is a general rule that because environmental impacts are greatest per unit activity for aerial releases, and are smallest for solid wastes, the design of the process reflects this hierarchy for the avoidance of generation of by-products).
• Proper design of abatement systems.
• Maximizing dispersion.

(b) Commissioning, operating and decommissioning plants, minimizing liquid and aerial discharges by means of:

• Prioritization in terms of dose impacts on the public. “To ensure resources are used in the most cost-effective manner, BNFL concentrates its ongoing research and development work on reducing those discharges which result in the highest doses or highest chemical toxicity, focusing effort on those areas in which there is the greatest potential for minimising environmental impact. For radioactive substances, it is generally the policy to use critical group dose as the key determining factor, though consideration is also given to collective doses” [84]. Table 19 shows that as of 2001 discharges, only a few radionuclides make almost all doses to the critical groups; this helps to identify where to intervene first in order to reduce risks to the population. Incidentally, the total critical group doses are within the BO–BL range of 0.02–1 mSv, as requested by the HSE.
• Increasing the magnitude of operations by decreasing the magnitude of wastes generated for eventual disposal.
• Addressing specific airborne emitted species: decreasing discharges of ⁴¹Ar, ¹⁴C and ¹²⁹I.
• Addressing specific water-borne emitted species: abating ¹³⁷Cs, ⁶⁰Co, ²³⁹Pu and ⁹⁹Tc.

(c) Developing new technologies.
(d) Implementing appropriate management systems.

Best available techiques

Concepts

According to the Convention for the Protection of the Marine Environment of the North-East Atlantic [13]: “The term ‘best available techniques’ means the latest stage of development (state of the art) of processes, of facilities or of methods of operation which indicate the practical suitability of a particular measure for limiting discharges, emissions and waste. In determining whether a set of processes, facilities and methods of operation constitute the best available techniques in general or individual cases, special consideration shall be

given to:

(a) comparable processes, facilities or methods of operation which have recently been successfully tried out;
(b) technological advances and changes in scientific knowledge and understanding;
(c) the economic feasibility of such techniques;
(d) time limits for installation in both new and existing plants;
(e) the nature and volume of the discharges and emissions concerned.”

Related to the application of BAT is the application of BEP, which is defined in the Convention [13] as “the application of the most appropriate combination of environmental control measures and strategies”. The Convention further states that [13]:

“In determining what combination of measures constitute best environmental practice, in general or individual cases, particular consideration should be given to:
(a) the environmental hazard of the product and its production, use and ultimate disposal;
(b) the substitution by less polluting activities or substances;
(c) the scale of use;
(d) the potential environmental benefit or penalty of substitute materials or activities;
(e) advances and changes in scientific knowledge and understanding;
(f) time limits for implementation;
(g) social and economic implications.”

In addition, BEP for a particular source will change with time “in the light of technological advances, economic and social factors, as well as changes in scientific knowledge and understanding” [13]. Finally [13]:

“If the reduction of inputs resulting from the use of best environmental practice does not lead to environmentally acceptable results, additional measures have to be applied and best environmental practice redefined.”

Regardless of the approach that is used for determining the optimal option, it should be recognized that judgements are required about the relative significance of the factors involved, which includes dialogue between the regulatory body and the operator, as well as other interested parties, particularly those who might be affected by the situation, facility or planned activity (e.g. local community representatives).
Formal decision aiding techniques may be used in the optimization process, especially for nuclear fuel cycle facilities. However, when the doses to the representative person are assessed to be very low (e.g. of the order of 10 μSv/a or less), a formal analysis of the optimization of protection is generally not necessary. The magnitude of exposure, the number of exposed individuals and the likelihood of exposure should be assessed for each of the options being considered. For complex facilities, elements of the radiological assessments should be made available at an early stage, and the development of the assessment may be an iterative process involving discussions between the operator, the regulatory body and other interested parties. The assessment should be refined as the development of the facility moves towards the stage at which an application for a licence for the planned facility is to be made (e.g. a licence to operate).

Application of best available techniques in environmental impact assessment

BAT assessment is typically undertaken when making decisions regarding the development and implementation of appropriate discharge standards to ensure environmental protection. This can include situations when standards for the discharge of radioactive material are being developed, for planning the management and disposal of radioactive waste, when authorizations are undergoing a significant amendment or when facilities are in a sensitive environment.
An example is provided here for the Gunnar Mine Site, which is an abandoned uranium mine and mill site in northern Saskatchewan, Canada. The site was operated between the late 1950s and early 1960s under a less stringent regulatory regime than today. Uranium ore was initially mined from an open pit from 1955 to 1961, and later, from an underground operation between 1957 and 1963. The Gunnar Mine Site officially closed in 1964, with little or no remediation of its facilities.
A stepwise decision tree approach was developed and applied to identify all potentially feasible remedial options, as part of the EIA process, and to map out key decision points during the licensing phase of the project, when final remedial options were selected from the list of options. Although the example provides an illustration of the approach for the remediation of the Gunnar Mine Site, the same approach can be used for optimization of the options intended for environmental protection.
A number of end points (or desired outcomes of the remediation efforts) were identified for the site, as follows:

• The site does not pose unreasonable public health or environmental risks.
• Flora and fauna adjacent to the site are not significantly affected by contaminants.
• Traditional use of resources adjacent to the site can be safely conducted.
• The desire is to have the site managed through an institutional controls programme for long term care and maintenance.

Screening framework for evaluation of remedial options

In conducting the alternatives assessment, all available options were identified and evaluated, including all aspects of each mine waste disposal alternative throughout the project life cycle, and all aspects of the project (direct or indirect) that may contribute to the predicted impacts associated with each potential option [124, 125]. The assessment considered the predicted quality and quantity of releases to the environment, and the corresponding predicted effects on the environment. The assessment of alternatives also considered the full cost of each remedial option throughout the project life cycle and its associated benefits, as an independent step from the technical review of options.
Assessment of the predicted quality and quantity of releases to the environment, and corresponding effects to the environment, are addressed through characterization of contaminant concentrations and key contaminant flow pathways, and subsequently inputting data into the human health and ecological risk assessment (HHERA).
Evaluation of remedial options was conducted using a multitiered assessment approach based on environmental and technical CR, utilizing the framework for assessment of alternatives proposed in Ref. [124], and which is presented in Table 20.

Table 20.

Step	Definition	Criteria	Analysis	Deliverable
1	Identify candidate alternatives	Threshold criteria	Mine waste disposal technologies Mine waste disposal storage options Mine waste disposal sites	Summary table Location maps
2	Prescreening assessment	Prescreening criteria	Prescreening evaluation	Summary table
3	Alternative characterization	Characterization criteria (accounts)	Environmental criteria Technical criteria Project economic criteria Socioeconomic criteria	Summary tables
4	Multiple accounts ledger	Evaluation criteria (subaccounts) Measurement criteria (indicators)	Qualitative value scales	Summary tables
5	Value based decision process	Scoring Weighting	Quantitative analysis	Summary tables
6	Sensitivity analysis	Reconsider weighting	Quantitative analyses	Summary tables
7	Document results			Final report

The summary of the major steps of the assessment provided in Ref. [125] specifies that these steps include:

• Development of a list of all possible candidate remedial options, with the input from stakeholders and without prior judgements;
• Screening of options to reduce the number and to provide assurance that any of the remaining options could prove to be the preferred option;
• Characterization of the remaining alternatives to ensure proper consideration of every aspect and nuance and the comparison of alternatives in a clear and concise format, to ensure complete transparency of the decision process;
• Identification of evaluation criteria that are linked to an effect and that easily differentiate the alternatives;
• Inclusion of quantitative value judgement in the decision process by scoring and weighting all evaluation criteria under the environmental, technical, economic and socioeconomic characteristics of each alternative;
• An assessment of the sensitivity of the decision making process.

An assessment of candidate Gunnar remedial options was conducted in general accordance with the framework for MCDA provided by Ref. [124], which is provided as a case study.

Remedial options analysis

A description of the key steps in remedial options analysis (see Table 23) was developed by Environment Canada in 2011 [124]. This approach has been applied to evaluate unfiltered candidate options for remediation at the Gunnar Mine Site.
Step 1: Identification of candidate alternatives
A first step in the assessment of remedial options is to develop a list of all possible candidate remedial options, with input from stakeholders and without prejudgement, i.e. to generate an ‘unfiltered’ list of remedial options [124, 125]. In doing so, a basic set of ‘threshold criteria’ (or ‘exclusion criteria’) may be established that can then be used in the prescreening of unfiltered options, as part of step 2 of the remedial options analysis.
For the purposes of options assessment, candidate alternatives were identified using a two phased approach: compilation of an unfiltered list of remedial options and then the evaluation of this list. The unfiltered list of remedial options that was generated during the first phase was distributed for review and input to responsible authorities, including provincial and federal regulatory and project partner stakeholder groups, in the second phase. The unfiltered remediation alternatives were generated to address each of the following Gunnar Site components, which were identified in the Gunnar EIA as the major ‘aspects’ of the site remediation:

• Waste disposal (i.e. disposal of waste generated by the demolition of former site infrastructure);
• Waste rock deposit;
• Open pit;
• Hydrocarbon contaminated soil;
• Waste rock seepage;
• Groundwater seepage;
• Gunnar main tailings (including tailings downstream of the dyke at the eastern boundary of the Gunnar main tailings deposit);
• Gunnar central tailings;
• Langley Bay/Back Bay (including tailings and aquatic receiving environment).

The candidate alternatives that were generated through this exercise constituted a broad list of waste disposal technologies, storage options and disposal locations, both on-site and off-site.
Step 2: Prescreening assessment
Following identification of the candidate remediation alternatives (as part of step 1 above), a prescreening assessment of the unfiltered list was conducted, based on threshold criteria (or exclusion criteria). The objective of the prescreening was to optimize the decision making process, with focus on an appropriate and manageable set of sufficiently detailed alternatives, as opposed to evaluating options that have obvious deficiencies [124].
Once the generic alternatives had been identified, based on reason, practicality and precedence, any ‘fatal flaw’ for each alternative was identified via preliminary screening. The screening of options was performed against threshold/exclusion criteria specific to the project objectives/desired end points. These criteria were established so as to generate a simple ‘yes’ or ‘no’ answer, dictating which alternatives were to be carried through to more detailed analysis. The established threshold (or exclusion) criteria were as follows:

• Does the alternative allow for compliance with a total external gamma dose criteria (mean value of ≤ 1 μSv/habove the background at a 1 m height, averaged over a 100 m × 100 m area and maximum value of 2.5 μSv/habove the background at a 1 m height, based on close out criteria for Cluff Lake, a uranium mine/mill sitein northern Saskatchewan further along in the decommissioning/remediation process than Gunnar [126])(Gunnar background = 0.7 μSv/h)? (Answer of ‘no’ indicates a fatal flaw.)
• Does the alternative allow for long term compliance with site specific/Saskatchewan Environment/Canadian Council of Ministers of the Environment guidelines/objectives/standards for soil and surface water quality? (Answer of ‘no’ indicates a fatal flaw.)
• Does the alternative allow for compliance with pertinent provincial/federal legislation? (Answer of ‘no’ indicates a fatal flaw.)
• Is the alternative a proven technology/has it been completed elsewhere with successful results? (Answer of ‘no’ indicates a fatal flaw.)
• Does the alternative improve the level of risk at the site? (Answer of ‘no’ indicates a fatal flaw due to an increase in risk.)
• Is there a potential risk of catastrophic failure? (Answer of ‘yes’ indicates a fatal flaw.)
• For waste disposal, is the proposed disposal site sufficiently large to accommodate waste? (Answer of ‘no’ indicates a fatal flaw.)

Each alternative receiving a positive evaluation (i.e. with no fatal flaws identified) was carried through a multiple accounts analysis (as demonstrated in Table 20), where the impacts from each alternative were assessed through a transparent scoring and weighting process.
Step 3: Characterization of alternatives
Once the prescreening assessment of candidate remedial alternatives had been completed, the remaining options required characterization. During options characterization, the options for each major site element were evaluated by a multidisciplinary project team consisting of individuals with expertise in the natural sciences, contaminant dynamics and engineering. Only potentially feasible alternatives were carried through to this stage of analysis. Feasible alternatives included those that could represent implementable remedial options, with no fatal flaws being identified during prescreening with respect to project objectives and end points. For clarity and differentiation from prescreening of remedial ‘alternatives’, potentially feasible alternatives that were carried through to detailed analysis were renamed as ‘options’ (as opposed to alternatives).
The outcomes of the evaluations of HHERA were derived in the context of the following broad evaluation criteria, which were developed for the site as part of the Gunnar EIA:

• Human health risks;
• Terrestrial wildlife and vegetation;
• Aquatic life and vegetation.

Within each of the above broad criteria, more detailed evaluation criteria (or ‘subaccounts’) were established, as described under step 4 below.
The focus of the evaluation of options with respect to HHERA was centred around potential option related chemical and radiological impacts to members of the public and the environment. In addition, physical impacts to terrestrial and aquatic life and vegetation were considered as part of the ecological risk assessment related evaluation criteria. As the Gunnar Mine Site has been secured and is not open to the public without orientation, and work activities are being planned and implemented to protect people, physical impacts to humans were considered as part of the evaluation of constructability.
The constructability evaluation was focused on the following two evaluation criteria:

• Potential risks to humans (i.e. workers) and the environment during the execution of the remediation (as part of the ‘active remediation phase’);
• Constructability/feasibility/efficacy of a given remedial option from a ‘practicability of execution’ perspective.

Following evaluation of remedial options with respect to HHERA and constructability, further screening was conducted to identify the potentially acceptable options based on public preference, gained through engagement of local communities and leaders, both through providing residents with information on the project, and receiving feedback and advice from communities. This was accomplished through community meetings, surveys and other forums, which provided important insight with respect to public preferences regarding the planning and implementation of the project, and which were considered in the evaluation of the Gunnar remedial options.
Step 4: Multiple accounts ledger
Following identification and characterization of alternatives in steps 1–3, it was necessary to then evaluate the options that were identified as potentially feasible, by identifying elements that could be used to differentiate them. This was accomplished through the development of a multiple accounts ledger, which consisted of the following two elements: subaccounts (also called evaluation criteria) and indicators (also called measurement criteria). Subaccounts (or evaluation criteria) were developed using the characterization criteria that had been selected during step 3. Unlike the characterization criteria, which were factual criteria that had been assigned with no a priori judgement being made regarding any of the alternatives under consideration, the evaluation criteria were developed with consideration of the material impact (benefit or loss) associated with each of the options under evaluation.
Evaluation criteria with respect to the Gunnar remediation project were, therefore, set in the context of three broad categories (or ‘accounts’): HHERA, constructability and public preference, as described above.
Within the above evaluation criteria, a number of qualitative and quantitative measurement criteria were established, which were then scored to identify potentially feasible remedial options.
The following measurement criteria were identified with respect to potential worker and ecological health risks during remediation:

• Physical hazards (safety risks);
• Worker health risks via exposure to non-radiological and radiological contaminants (soil or dust inhalation, dermal contact), ambient radon exposure and external radiation exposure;
• Risks to terrestrial wildlife generated;
• Risks to aquatic life generated.

The following measurement criteria were identified with respect to constructability, feasibility and efficacy during remediation:

• Estimated construction duration;
• Cost;
• Ability to mitigate pertinent exposure pathways;
• Regulatory acceptance;
• Long term waste generation;
• Requirement for control, monitoring and/or maintenance (i.e. institutional control).

The possible Gunnar remedial options were evaluated in the context of a single integrated measurement criterion that has been identified as ‘public preference’, which was scored as described in further detail below.
Step 5: Value based decision process
Once a multiple accounts ledger had been created, with criteria to facilitate the evaluation and measurement of possible remedial options, it was necessary to score and weight all the indicators, subaccounts and accounts, such that merit ratings for each option could be quantitatively determined. In doing so, the following processes were undertaken:

• Scoring;
• Weighting;
• Quantitative analysis.

Scoring of the possible Gunnar remedial options from the perspective of HHERA in the long term was conducted using both quantitative and qualitative measurement criteria. Quantitative criteria were based on the concentrations of contaminants released to the environment in the long term for a given option relative to environmental quality guidelines, whereas qualitative criteria provided a relative comparison of remedial options in cases for which no quantitative guidelines existed against which measurement criteria could be compared. On this basis, the following scoring criteria were developed:

• A value of 0 indicates exceedance of the guideline by 100-fold or greater/physical risk that exceeds the baseline risk; this option performs very poorly against listed criteria.
• A value of 1 indicates exceedance of the guideline by 10- to 100-fold/physical risk that is similar to the baseline risk; this option is the same or has a very small improvement compared with the existing situation.
• A value of 2 indicates exceedance of the guideline by 1- to 10-fold/physical risk that is lower than the baseline risk; this option has a moderate improvement compared with the existing situation.
• A value of 3 indicates not applicable; this option has no exceedance of guideline values or a large improvement compared with the existing situation/best performing option.

To differentiate the performance of the options versus the prescribed criteria, numerical rankings were assigned as a quantitative indicator of impact. The following measurement scheme was used with respect to constructability:

• A value of 0 indicates the option performs very poorly against listed criteria.
• A value of 1 indicates the same or a very small improvement compared with the existing situation.
• A value of 2 indicates moderate improvement compared with the existing situation.
• A value of 3 indicates not applicable/large improvement compared with the existing situation/best performing option.

In terms of options that were ‘do nothing’ or very near to do nothing, many of the criteria in the technical analysis were evaluated as ‘not applicable’. These not applicable designations were given a ranking of 3, to indicate a high ranking in terms of subaccounts, such as duration or cost, in comparison with options for which some action is taken.
Scoring of each remedial option with respect to public preference was undertaken using an integrated approach to incorporate information that had been received from community members and leaders through a diversity of consultation approaches. The outcomes of such approaches, which included community meetings, flyers, surveys and many others, were used to inform the scoring in the context of the following scoring criteria:

• A value of 0 indicates this option is unacceptable or that local communities are opposed to the option.
• A value of 1 indicates local communities would consider it as a possible option, but with reservations.
• A value of 2 indicates local communities would consider it as a possible option.
• A value of 3 indicates local communities would consider it as a preferred option.

It should be noted that in assigning scores of 1 versus 2 above, values were set to distinguish options that were considered possible by local communities, in one case, with reservations, and in the second case, with few to no reservations. For example, a score of 1 was assigned for options involving transport of hazardous materials across Lake Athabasca. In such scenarios, it was necessary for activities to be conducted in close consultation with communities owing to the value that northern communities place on water quality and the concerns of catastrophic releases of hazardous materials to Lake Athabasca. Despite these reservations, it was possible to transport hazardous materials across the winter ice road, working closely with local communities.
As part of the analysis, weighting factors were applied to the raw scores that had been generated during the evaluation of possible Gunnar remedial options. In this way, it was possible to assign a relative importance of a given measurement criterion compared to others.
As a preliminary step, weighting factors were assigned to each of the three accounts (HHERA, constructability and public preference), as follows:

• A value of 40% for HHERA;
• A value of 40% for constructability;
• A value 20% for public preference.

Within each of the above three accounts, individual measurement criteria were also weighted and justified to reflect their relative importance.
Once scoring and weighting of each possible remedial option was completed, it was necessary to conduct a quantitative analysis of the information. This involved compiling the indicator value S (‘score’) for each indicator (or measurement criterion), along with the weighting factor W, and calculating the product of these to generate a combined indicator merit score (S·W) for each possible remedial option [124].
Based on these data, it was possible to take the sum of the indicator merit scores for each evaluation criterion (or subaccount) to generate a subaccount merit score for each, i.e. Σ{S·W}. Within a given subaccount (or evaluation criterion), the resultant subaccount merit scores could then be directly compared across possible remedial options. To facilitate further comparison of each subaccount merit score against values for other subaccounts, the scores were normalized to the same point scale used to score each indicator value. In doing so, the subaccount merit score was divided by the sum of the weightings (Σ W) to yield a subaccount merit rating [124]:

$R_{S}={\frac {\sum {S\cdot W}}{\sum {W}}}$; (7)

The same procedure can be undertaken to weight and normalize scoring for accounts (in this case, HHERA, constructability and public preference) to generate account merit scores (Σ{Rs·W}) and account merit ratings (Σ{Rs·W}/ΣW) for each remedial option.
As a final step, option merit scores (Σ{Ra·W}) and option merit ratings (Σ{Ra·W}/ΣW) can be determined for each possible Gunnar remedial option.
It should be noted that even with the multiple layers of analysis, it is possible for certain options to score identically, against all criteria, for a certain aspect of the site. In the event of such scoring/ranking, the performance of the option needs to be measured against the total available score, as described below.
Step 6: Sensitivity analysis
Any decision making process will be inherently subject to some degree of bias and subjectivity. Therefore, it is important that a framework is followed to ensure that any decisions arising from the options screening and selection process are transparent and reproducible by external reviewers [124]. With this in mind, the options analysis was completed for the Gunnar Mine Site in multiple tables, rating the potential remedial options separately with respect to performance against: (i) HHERA, (ii) constructability and (iii) public preference, to allow for such transparency.
A sensitivity analysis can involve a very large number of permutations and combinations, which in itself can impose bias and subjectivity. Therefore, for the purposes of the Gunnar evaluation, the sensitivity analysis was kept simple, with the ultimate goal of evaluating the impact of the respective indicator weights (W) on the selection of potentially feasible remedial options, based on the initial ranking (i.e. assignment of a value of 0–3 for each measurement criterion and remedial option combination). As such, the analysis was conducted by simply setting all weightings to a value of 1, effectively removing the value bias between one measurement criterion and another. In this case, remedial options achieving relatively higher sums of indicator values measured against the measurement criterion values may be more feasible for a given site aspect than those with lower indicator values. A sensitivity analysis was conducted to evaluate this.

Summary of the study results

An assessment of candidate remedial options was conducted in general accordance with the framework for MCDA provided by Ref. [124]. The analysis consisted of multiple stages of analysis, as demonstrated in Table 23. Based on this approach, a comprehensive, unfiltered list of possible remedial options for the Gunnar Mine Site was evaluated and scored to identify potentially feasible remedial options. For the purposes of this analysis, a potentially preferable option was identified as the option for which the highest option merit rating was determined. Owing to the inherent complexity of the Gunnar remediation project, it was necessary to subdivide remedial options into a number of interconnected site aspects (e.g. submerged and unsubmerged unconfined tailings, waste rock piles, open pit, etc.), which were individually scored as separate matrices, with respect to HHERA and public preference.
Based on this analysis, potentially preferable remedial options were identified to address each Gunnar Site aspect; however, due to the lack of historical records and monitoring data, it was not possible to identify a single, ‘preferred’ remedial option. Instead, potential remedial options could be subdivided into three categories [127]:
(a) Options that are relatively straightforward to implement, with little uncertainty, e.g. covering unconfined tailings, water diversions, removal of contaminated debris from waste rock piles and addressing physical hazards associated with unstable slopes on the waste rock piles.
(b) Options that require additional monitoring data and follow-up assessment prior to selection of a final remediation approach, e.g. further surface water and hydrogeological monitoring to determine contaminant transport pathways between sources and receiving environments.
(c) Options that are dependent upon the selection of remedial approaches for other site aspects that have to be determined before the first one can proceed, e.g. decisions on the pit cannot be determined until it has been decided if the waste rock will be placed in the pit or covered and left in place.

Appendix IV

Concept of collective dose
The concept of collective dose was found to be very useful for comparative analysis of radioactive emissions from nuclear facilities and systems.

Introduction

Interpretation of the collective dose has been discussed by the ICRP, which, in its recommendations [128], believes that the use of the collective dose concept is closely connected with formal CBA. The product of the average dose to an individual and the number of individuals in a group (i.e. how collective dose has been calculated in the past) is a legalized quantitative value, but it is of a limited application, as it combines redundant information. For decision making, the necessary information has to be presented as a matrix that indicates the number of individuals exposed to a specific dose and the date it was received. This matrix needs to be considered as an auxiliary decision making tool allowing the significance evaluation of individual matrix elements. The matrix approach leads to a more correct estimation of consequences (risks) of irradiation. The ICRP believes that this will avoid misinterpretation of the collective dose, which has resulted in serious errors in the prediction of lethal outcomes. A justification of these ICRP recommendations can be found in Ref. [128].
Collective doses are generally not used by regulators; instead, regulators usually limit the emission of single radionuclides or classes of radionuclides represented by equivalent isotopes on the basis of doses to the critical group. However, collective doses normalized per unit of electricity were used in the ExternE project for the calculation of external costs for comparing different power technologies [110, 111, 119]. Annual collective doses have also been used for comparison of different options of nuclear cycles in Ref. [116]. Recommendations on how collective doses should be calculated in particular cases can be found in Refs [23, 129, 130].
Use of collective doses also presents some disadvantages, e.g. the possibly prevailing importance given to very low doses occurring over very long time periods (applying the linear dose effect relationship without cut-offs), the dependency on key modelling assumptions that are not easily controllable such as population distributions (in place and time) and the application, or not, of discounting.

Simplified determination of collective dose

The IAEA generic models (see also Appendix II) include a simplified method to determine collective doses. In section 7 of Ref. [23], tables contain collective effective dose commitments per unit activity (man Sv/Bq) of radionuclides discharged to the atmosphere, to marine water and freshwater bodies. All contributions from individual radionuclide species and pathways need to be summed.
The simplified conversion of release rates to dose factors has been derived using the results of two approaches: one based on a simple method using generic parameters [98] and the other one based on complex modelling [131], which have been developed by the NRPB, in the United Kingdom. Reference [23] suggests using simplified models with caution, noting that they can only provide order of magnitude estimates, and that collective doses:

“...should be used only as part of a screening or generic assessment procedure, for example to ensure compliance with dose limiting criteria or as input to an optimization exercise to compare options as part of an intuitive, semi-quantitative analysis. They should not be used for more rigorous optimization analyses, such as cost–benefit analyses, nor for other purposes.”

Reference [23] further states that “the site specific discharge conditions and the actual critical group location be taken into account if the predicted doses exceed a reference level of around 10% of the dose constraint.”
Collective doses were estimated for most radionuclides only in local and regional zones, which may extend from the point of release to distances varying from about a hundred kilometres to several thousand kilometres [23]. Four nuclides were considered for global analysis because of their relatively long radioactive half-lives or a high environmental mobility: ¹⁴C, ³H, ¹²⁹I and ⁸⁵Kr; other long lived radionuclides, such as ²³⁷Np or ⁹⁹Tc, may also become globally dispersed following discharge, but they have not yet been accurately addressed. Therefore, an analyst may need to consider these (and others), depending on the technical characteristics and expected performance of the NES.
Collective doses can be used for the purposes of optimization of radiation protection measures. WS-G-2.3 [33] recommends using the estimations of collective dose arising from discharges to avoid spending resources to assess options for reducing discharges in disproportion to the likely improvement in radiological protection. The collective dose from discharges, which can be estimated using Ref. [23], should be added to an estimate of the relevant collective dose from occupational exposure to provide an estimate of the total collective dose. If the result is less than about 1 man Sv/a, an extensive formal optimization study most probably will not be needed [132]. If the value of the collective dose is greater than about 1 man Sv/a, a formal study by the designer (technology developer) is

required, with the use of decision aiding techniques such as CBA and multicriteria methods.