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 15, 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]: $R_{i,j}^{k}=A_{i,j}^{k}\times {DCF}_{i,j}^{k}$ 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: $R^{k}=\sum _{1}^{3}\sum _{1}^{N_{j}}R_{i,j}^{k}$ 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: $R^{T}=\sum _{1}^{M}R^{k}$ 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 I

Important stressors in nuclear energy systems

Introduction

This appendix, including the tables, is based on Ref. [30]. It presents illustrative lists of important stressors for facilities of an NES with a water cooled reactor using UOX or MOX fuel.
Important radionuclides, chemicals and other stressors which are relevant for various facilities of an NES with a water cooled reactor using UOX or MOX fuel are presented in Sections I.2–I.9, based on current experience. However, it is recommended that, especially, in the case of an innovative design of an NES facility, this list should be revised based on the actual radionuclide and chemical inventories in the innovative NES facility, their toxicity and their environmental mobility.
In the case where calculation of the impact of stressors is necessary, it is desirable to maintain a conservative approach, and to use internationally accepted models, such as those presented in Appendix II, or available licensed national models. Model descriptions with appropriate references should be documented in the INPRO assessment report.
The main facilities of an NES with a water cooled reactor using UOX and MOX fuel are as follows: mining and milling of uranium ore, refining and conversion of uranium ore, enrichment of uranium, fabrication of nuclear fuel, power generation, reprocessing of nuclear fuel, and radioactive waste storage and disposal including waste from decommissioning. Some facilities of an NES have greater environmental impacts compared to others; all facilities have specific stressors and impacts, and therefore each facility should be considered separately. Depending on the scope of a specific Nuclear Energy System Assessment, only some of the NES facilities could be considered.
It should be mentioned that there are about 200 radionuclides which are specific to the different stages of the nuclear fuel cycle and the reactor operation and which can cause radiation impacts on the environment. In the following sections, only relatively long lived radionuclides are mentioned for each facility. However, it should be recognized that short lived progenies, which are in equilibrium with some parent radionuclides, can essentially contribute to the doses to public and biota species for many contamination scenarios. Some of these short lived radionuclides are not discussed here explicitly; however, it is implied that their contributions to doses have to be taken into account together with the impacts from their parent radionuclides in radiation impact analyses (e.g. see Appendix II).

Mining of uranium ore

The environmental impacts of mining of uranium ores may involve the disruption of land surface and water bodies, the release of radionuclides to air and water, the release of heavy metals and acids, the emission of particulates, etc. In 2011, for example, conventional uranium mining produced 47% of the world’s uranium — 18% from open pits and 29% from underground mines [55]. Non-conventional methods have also been used for uranium production, such as in situ leaching (ISL), which produced 42% of the world’s uranium in 2011. The environmental impacts of a uranium mine are potentially numerous and diverse, depending on the mining technologies used [56].
The environmental impacts of mining activities are measured using several criteria14. Individual dose is normally used as the criterion for the radiological impact on humans and non-human species. Several other criteria are used for the non-radiological environmental impact and for the radiological impact on the environment other than humans.
Usually, baseline studies are conducted before any mining activities are undertaken; these studies are to be used when establishing environmental quality objectives needed for the construction, operation, decommissioning and postdecommissioning phases. In other cases, there are pre-established air, sediment, water and groundwater quality objectives that need to be met. Social, aesthetic, economic and recreational values are met by establishing requirements to preserve parts of the affected ecosystem, e.g. fish spawning areas and the habitats of endangered species may need to be preserved for economic or social and ecological reasons.

Radionuclides of concern

Uranium ore contains natural occurring radioactive material (NORM), which includes uranium isotopes (mainly ²³⁸U) and uranium progenies (see Fig. 4) such as ²³⁰Th and ²²⁶Ra. The radioactive decay of the latter nuclides produces ²²²Rn (an inert gas), which is normally responsible for the biggest part of exposure to workers in the mines and often to the public.

FIG. 4. Chain of decay of ²³⁸U (gamma emitters not marked)[1].

The important radionuclides which have to be considered in the environmental assessment are: ²¹⁰Pb, ²¹⁰Po, ²²⁶Ra, ²²²Rn, ²²⁸Th, ²³⁰Th, ²³²Th, ²³⁴Th, ²³⁴U, ²³⁵U and ²³⁸U. The environmental impact from ²²⁷Ac (a decay product of ²³⁵U) is also recommended to be studied. As mentioned above, short lived progenies such as ²¹⁴Bi and ²¹⁴Pb (both progenies of ²²²Rn, see Fig. 4) are responsible for a large portion of the radiation impact, but are not listed here because they are always in equilibrium with ²²²Rn.
For the majority of these radionuclides (except for ²²²Rn), contamination of water with radionuclides is the most important exposure pathway. The radioactivity of water is generally stipulated by the dissolved uranium, thorium, radium and lead ions. However, an aerial pathway can be also important for several radionuclides, e.g. ²²⁶Ra, ²³⁰Th and ²³⁸U.
Some natural radionuclides, e.g. uranium, provide both radiation and chemical environmental impacts, which also have to be taken into account in the assessment.

Chemicals of concern

Water contaminated with chemicals (including NORM) is produced by dewatering of underground and open pit mines, surface water runoff from and seepage through the waste rock piles and ore stockpiles, and ISL restoration activities. In situations when the ore includes pyrites, the generation of acid requires neutralization as part of the water treatment process, if this water is planned to be discharged to the environment. Acid generation is a concern of all types of mining because the acid solubilizes and increases the mobility of heavy metals, and for uranium mining, it also mobilizes radionuclides. Utilization of explosives in mining may add some nitrites, nitrates and ammonia to the mine wastewater.

Other stressors

Examples of other stressors are:

• Temporarily committed land, e.g. for a current NES (using an open fuel cycle with light water reactors (LWRs)), this value is estimated to be about 25 ha/GW(e) for open pit mining [30];
• Permanently committed land;
• Dust, originating at exposed ore stockpiles, ore haul roads, etc.

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from uranium ore mining is presented in Table 3.

Table 3. Illustrative list of stressors for evaluation of environmental impact from uranium ore mining

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Pb-210	Water*	MBq/tU or MBq/GW·a	MBq/a or MBq/d
Po-210	Water
Ra-226	Air, water
Ra-228	Air, water
Th-228	Air, water
Th-230	Air, water
Th-232	Air, water
Th-234	Air, water
U-234	Air, water
U-235	Air, water
U-238	Air, water
Rn-222	Air
Ac-227	Air, water
Chemicals
As	Water	kg/tU or MBq/GW·a	kg/a or kg/d
Se	Water
Ni	Water
Nirites	Water
Nitrates	Water
Ammonia	Water
Sulphates	Water
Others
Land temporarily committed	Soil	m2/tU or m2/GW	m2 (total area)
Land permanently committed	Soil
Dust	Air	kg/tU	kg/a
Solids dissolved	Water	kg/tU	kg/a
Solids suspended	Water	kg/tU	kg/a

* Water comprises surface water as well as groundwater

Milling of uranium ore

Usually, uranium ore is processed close to the mine to limit transportation costs. The typical process for the extraction of uranium consists of crushing and grinding of the ore, followed by chemical leaching with sulphuric acid or an alkali carbonate solution. Acid leaching is the more common method; however, some mills use alkaline leaching when the ore body contains limestone or similar basic constituents, which would consume uneconomic quantities of acid. The uranium solution is purified and concentrated by ion exchange and/or solvent extraction technology. The uranium is then precipitated from solution, filtered and dried to produce a concentrate, known as yellowcake, which contains between 60% and 90% uranium by weight.
Potential sources of impacts on the environment from mill tailings comprise the following types of release: (i) escape of gaseous radon; (ii) transport of radioactive particulates by the wind; (iii) contamination of surface water and groundwater through runoff or seepage of radionuclides, heavy metals or other toxic materials; and (iv) dispersion of tailings over a wide area caused by erosion or flooding.

Radionuclides of concern

At the stage of milling, radionuclides of concern are similar to those which are considered for mining. The tailing slurry is the most significant source of radionuclides. Mill sites in dry areas give rise to effectively no liquid effluents. However, the runoff water from mills in wet climates will contain radionuclides and may need treatment before release into watercourses. The tailings are characterized by their relatively large volumes and relatively low activity concentrations of long lived natural occurring radionuclides. About 15% of the total radioactivity which was originally contained in the ore is retained in the yellowcake produced by the mill. Once shorter lived radioactive nuclides have decayed, some 70% of the radioactivity originally present in the ore is left in the tailings. The tailings contain nearly all of the naturally occurring radioactive progenies from the decay of uranium, notably ²²⁶Ra and ²³⁰Th. The presence of ²³⁰Th provides a long term source of radon emission. Radioactive airborne effluents from milling may include dusts and radon gas released into the air from ore stockpiles, crushing and grinding of ore, drying and packing of yellowcake, and the tailings retention system. The releases of dusts produced in the processing operations are reduced by ventilation extract scrubbers. Tailings may be a continuing source of radon and radioactive dust after milling operations have ceased. Thus, the list of radionuclides that have to be evaluated for milling is similar to the one for mining.

Chemicals of concern

Contaminated water is discharged from uranium mills to tailing management facilities. The contaminants include heavy metals, sulphates, chlorides, organics and ammonia. The exact mixture will depend on such factors as type of process used and ore grade, and should be evaluated separately for each case.
Airborne chemical contaminants released to the environment include combustion products (oxides of carbon, nitrogen and sulphur) from the process steam boilers and power generation, sulphuric acid fumes in small concentrations from the leach tanks and vaporized organic reagents from the solvent extraction ventilation system. In addition, from some plants where sulphuric acid is made on-site, sulphur dioxide is released to the atmosphere.

Other stressors

It is estimated that currently an average of about 4 ha of land area is required for milling of uranium ore sufficient to produce 1 GW(e) of energy in a once through fuel cycle. About 75% of this land is devoted to impoundment for the permanent disposal of mill tailings. The amount of land required is highly dependent on the grade of ore being processed. Lower grade ore milling operations normally use more land per GW(e) compared with facilities processing higher grade ore.

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from uranium ore milling is presented in Table 4.

Table 4. Illustrative list of stressors for evaluation of environmental impact from uranium ore milling

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Pb-210	Water	MBq/tU or MBq/GW·a	MBq/a or MBq/d
Po-210	Water
Ra-226	Air, water
Th-228	Water
Th-230	Air, water
Th-232	Water
Th-234	Water
U-234	Water
U-235	Water
U-238	Water
Rn-222	Air
Ac-227	Water
Dust (total alpha activity)	Air
Chemicals
Heavy metals	Water	kg/tU or MBq/GW·a	kg/a or kg/d
Organic	Water
Chlorides	Water
Ammonia	Water
Sulphates	Air, water
Others
Land temporarily committed	Soil	m2/tU	m2 (total area)
Land permanently committed	Soil
Dust	Air	kg/tU	kg/a
Solids dissolved	Water	kg/tU	kg/a
Solids suspended	Water	kg/tU	kg/a

Refining and conversion of uranium ore to uranium hexafluoride

Uranium ore concentrate (UOC) may consist of any of several different uranium compounds. It still contains elements other than uranium and some uranium radioactive decay products. UOC is refined to obtain higher purity uranium compounds. Two different processes — wet and dry — are used to purify UOC and convert it into a usable form. The more commonly used process, the wet process, consists of dissolving UOC in nitric acid and refining it by solvent extraction. The pure uranyl nitrate formed is then converted to uranium trioxide, which can be converted to uranium dioxide (UO₂) for natural uranium fuel, or converted progressively to uranium tetrafluoride and uranium hexafluoride (UF₆) for enrichment to produce LWR fuel

Radionuclides of concern

Emissions from uranium refining and conversion facilities are relatively minor. The only radioactive emission of significance is natural uranium, which may be emitted as dust or as a volatile reaction product of UF₆ [30]. The plants are equipped with dust collectors and scrubbers to mitigate the impacts of these emissions.
The effluents from the wet and dry processes of UF₆ production differ substantially. In the wet process, most of the impurities entering with UOC are rejected in the raffinate solution from solvent extraction, whereas in the dry process, most of the UOC impurities are contained in solid wastes from the fluorination and distillation stages. In the case when raffinate from the wet process is recycled through the uranium mill where residual uranium is recovered and the remaining waste is disposed of with the tailings, the radiological impact of the raffinate is included in the radiological impact of the milling facility. Where the raffinate is not recycled, the radiological impact is due to residual thorium and, to a lesser extent, radium.

Chemicals of concern

Atmospheric emissions from the refining and conversion processes contain greenhouse gases such as NOX. Aqueous release may contain residual tributylphosphate and heavy metals that could have a potential impact on benthic fauna. Other contaminants with potential for environmental impacts are nitrates, and, under accident conditions, ammonia and fluorides may also be released.

Other stressors

Of the temporary land commitment for a UF₆ production plant (~1.3 ha/GW(e)), approximately 10% is needed for roads, fills and plant structures [30]. Approximately 1% of land needed for a plant is permanently committed for waste burial.

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from refining and conversion is presented in Table 5.

Table 5. Illustrative list of stressors for evaluation of environmental impact from refining and conversion to uranium hexafluoride

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Pb-210	Water	MBq/tU or MBq/GW·a	MBq/a or MBq/d
Po-210	Water
Ra-226	Air, water
Th-228	Air, water
Th-230	Air
Th-232	Air
Th-234	Air, water
U-234	Water
U-235	Air, water
U-238	Air, water
Chemicals
Heavy metals (have to be specified within the assessment)	Water	kg/tU or MBq/GW·a	kg/a or kg/d
Fluorides	Air, water
Nitrogen oxides	Air
Sulphur oxides	Air
Carbon monoxide	Air
Volatile organic compounds	Air
Tributylphosphate	Water
Others
Land temporarily committed	Soil	m2/tU or m2/GW	m2 (total area)
Land permanently committed	Soil
Heat rejected	Air	MW(th)/tU	MW(th)/a
Solids dissolved	Water	kg/tU	kg/a
Solids suspended	Water	kg/tU	kg/a

Enrichment of uranium

LWRs normally use uranium enriched to about 4–5% in 235U. Current commercial enrichment technologies are based on gaseous diffusion or centrifugation of uranium isotopes in the form of UF₆. Reference [57] briefly explains the gas diffusion process as follows:

“In the gaseous diffusion process, gaseous UF₆ is compressed and passed over a porous membrane. Molecules of UF₆ containing the lighter isotope, uranium-235, diffuse through the membrane more rapidly than those with the heavier uranium-238 isotope; consequently, the UF6 passing the membrane has a slightly greater proportion of molecules containing uranium-235. The degree of enrichment for one membrane is minute and over a thousand successive diffusion stages are necessary to raise the proportion of uranium-235 from the naturally occurring level of 0.71 per cent to the 2–4 per cent required in the product stream, with about 0.25 per cent in a reject ‘tails’ stream.
“Each stage requires recompression of the gaseous hexafluoride. Uranium enrichment by gaseous diffusion requires large quantities of electrical energy. About 36.5 MWe-y of electricity would be needed by a gaseous diffusion plant to enrich the uranium for the generation of 1 GWe of electricity in a LWR”.

For the the uranium enrichment by centrifugation process, Ref. [57] provides the following simplified description:

“During enrichment by gas centrifugation, molecules of UF₆ containing the heavier isotope uranium-238 migrate preferentially to the wall of a rapidly rotating cylinder. There is a consequent enrichment in the lighter uranium-235 isotope in the gas near the tube axis. The separation factor is greater than in the diffusion process, and the two streams removed from the tube axis and wall require only tens of stages arranged in a cascade to produce the required percentages of uranium-235 in the product and the reject tails. High centrifugal stresses limit the size of the equipment, and many parallel cascades involving hundreds of thousands of centrifuges are required to achieve the separative capacity of a commercial enrichment plant.”

Radionuclides of concern

Emissions of radionuclides from the enrichment process are generally small and consist essentially of long lived uranium isotopes, such as ²³⁴U, ²³⁵U and ²³⁸U, together with ^234mPa and ²³⁰Th, which are the short lived decay products of ²³⁸U. The long half-life of ²³⁰Th prevents activity buildup of any other radionuclide of the ²³⁸U series. For current facilities, the radiological impacts on the public and non-human species are negligible. At the Capenhurst enrichment site in the United Kingdom, doses to the critical group members of the public are estimated to be less than 0.01 mSv per year.

Chemicals of concern

The enrichment plant itself generates small quantities of airborne fluorides and oxides of nitrogen and sulphur from the process cooling systems, process cleanup operations, on-site steam plant and auxiliary production facilities. Uranium losses in the effluents are very low. Some sludge from container cleanup operations is usually retained on-site. The depleted uranium residue from enrichment plants is normally stockpiled for possible future recovery of the remaining fissile material. The depleted uranium can be used in the future as a resource, and is therefore not considered as a release (or waste). It is noted that near current enrichment facilities, the concentrations of gaseous and liquid effluents are below the ranges for which deleterious effects have been observed.

Other stressors

Essentially, none of the land required for enrichment facilities is committed permanently. The temporary land requirement is estimated to be 0.3 ha/GW(e). Water is required for the operation of cooling towers associated with the gaseous diffusion process and also for the large amounts of electricity that need to be generated. For enrichment by gaseous diffusion, 92% of all the electricity required in a nuclear fuel cycle up to fuel fabrication is consumed in enrichment. Other enrichment techniques such as centrifuges require less than one tenth of the electricity needed for a gaseous diffusion plant.

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from an enrichment plant is presented in Table 6.

Table 6. Illustrative list of stressors for evaluation of environmental impact from an enrichment plant

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Ra-226	Water	MBq/tU or MBq/GW·a	MBq/a or MBq/d
Rn-222	Air
Tc-99	Air, water
Th-234	Air
U-234	Air, water
U-235	Air, water
U-238	Air, water
Chemicals
Fluorides	Air, water	kg/tU or MBq/GW·a	kg/a or kg/d
Nitrogen oxides	Air
Sulphur oxides	Air
Carbon monoxide	Air
Volatile organic compounds	Air
Tributylphosphate	Water
Others
Land temporarily committed	Soil	m2/tU or m2/GW	m2 (total area)
Land permanently committed	Soil
Dust	Air	kg/tU	kg/a
Dust (radioactive)	Air	MBq/tU	MBq/a
Solids dissolved	Water	kg/tU	kg/a
Solids suspended	Water	kg/tU	kg/a

Conversion to uranium dioxide and fuel fabrication

The required material for the fabrication of fuel for an LWR is UO₂. The UF₆ (enriched to about 4–5% in ²³⁵U) is converted to UO₂ powder, which is formed into pellets, sintered to achieve the desired density and ground to the required dimensions. Fuel pellets are loaded into tubes of zirconium alloy (zirconium–tin or zirconium–niobium), which are sealed at both ends. These fuel rods are spaced in fixed parallel arrays to form reactor fuel assemblies.

Radionuclides of concern

The radionuclides of concern are about the same as those described in Section I.5 for enrichment. The most important pathway of the population and non-human species exposure is inhalation. The doses due to liquid discharges are much less than those from airborne discharges.

Chemicals of concern

The effluent from fuel fabrication with the greatest potential environmental impact is chemical in nature. Hydrogen fluoride (HF) is potentially the most significant airborne chemical effluent from fuel fabrication. Liquid effluent from fuel manufacture contains nitrogen compounds formed from ammonia in the production of UO₂ powder and by nitric acid in the scrap recovery operations. Very small quantities of uranium are released with the effluent gases and liquids. Ammonia and nitrates are found in liquids released from the waste holding ponds.
In a dry fuel production process, the emissions of HF to the environment are very small. Nearly all of the HF produced will be removed from the off-gas by the condensing and cleaning system. The end products, liquid HF and CaCO₃/CaF₂, are suitable for industrial use. Thus, the non-radiological impacts are mitigated by the recovery and recycling of potential contaminants.

Other stressors

The temporary land requirement is estimated to be 0.1 ha/GW(e) for an NES with an LWR reactor. All of the land required for fuel fabrication can be reclaimed by conventional techniques. Care would have to be taken when decommissioning the holding ponds or lagoons. The facility requires water, most of which is used for cooling of plant processes. The water does not come into contact with uranium or process chemicals during operation. In the dry process, there is no cooling water discharge.

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from UO2 fuel fabrication is presented in Table 7.

Table 7. Illustrative list of stressors for evaluation of environmental impact from uranium dioxide fuel fabrication

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Ra-226	Air	MBq/tU or MBq/GW·a	MBq/a or MBq/d
Th-234	Air
U-234	Air, water
U-235	Air, water
U-238	Air, water
Chemicals
Fluorides	Air, water	kg/tU or MBq/GW·a	kg/a or kg/d
Nitrogen oxides	Air
Ammonia	Water
Others
Land temporarily committed	Soil	m2/tU or m2/GW	m2 (total area)
Land permanently committed	Soil

Mixed oxide fuel fabrication

Two processes are currently used to produce MOX fuel; these processes differ mainly at the beginning, owing to the nature of their feed materials. For the dry process, the feed materials are UO₂ (ammonium uranyl carbonate, ammonium diuranate and integrated dry route) and PuO₂ powders. The alternative wet process starts with plutonium and uranium nitrate solutions. MOX powder is prepared by co-milling or co-conversion, depending on the type of feed material.
Following the main fabrication, the steps (pelletizing, sintering, rod fabrication and assembling) are comparable with those of uranium fuel fabrication. The main difference to UO2 fuel fabrication is related to a strict alpha activity containment of the processed material in tight gloveboxes and shielding against gamma and neutron radiation.

Radionuclides of concern

Atmospheric discharges result from ventilation — for dynamic containment purposes — of production buildings and gloveboxes wherein the manufacturing process is performed. The discharges consist of aerosols of uranium/plutonium.
Very low alpha active liquids, principally from cleaning of non-contaminated or very low contaminated areas (operators, floors, etc.), are discharged into the environment after nuclear control measurements (range of activity: 1–5 kBq/m³). The balance of discharged activity is exactly maintained.
Liquid discharges increase with the throughput of a plant (these discharges mainly depend on the number of workers and the surface of the buildings); typical discharged activities are in the range 0.5–3 MBq/a.

Chemicals of concern

The chemical emissions from this process are negligible (for the dry process, there are no chemical emissions).

Other stressors

Basically, MOX fuel fabrication is a recycling activity. Plutonium is a valuable fissile material originating from the reprocessing of UO₂ spent fuel. The replacing of ²³⁵U by plutonium in LWR fuel contributes to a more efficient use of uranium resources. In most cases, for the fuel matrix, natural uranium, depleted uranium and reprocessed uranium can be used. Utilization of other resources (e.g. energy, fluids and land) is comparable with those used in UO₂ fuel fabrication. The land requirement is estimated to be 3 ha/GW(e). The dry process does not use water, and its energy requirement is estimated to be 0.3 MW/a per GW(e).

Illustrative list of stressors

An illustrative list of stressors for evaluation of the environmental impact from MOX fuel fabrication is presented in Table 8.

Table 8. Illustrative list of stressors for evaluation of environmental impact from mixed oxide fuel fabrication

Stressor	Media type	Normalized release units	Average release units
Radionuclides
Pu	Air	MBq/tU or MBq/GW·a	MBq/a or MBq/d
U-234	Air, water
U-235	Air, water
U-238	Air, water
Others
Land temporarily committed	Soil	m2/tU or m2/GW	m2 (total area)
Land permanently committed	Soil