Criterion
Criterion (CR) (or more than one) is required to enable the INPRO assessor to
determine whether and how well a given user requirement is being met by a given INS. An
INPRO criterion consists of an Indicator (IN) and an Acceptance Limit (AL). Indicators
may be based on a single parameter, on an aggregate variable, or on a status statement.
Two types of indicators of INPRO criteria are distinguished, numerical and logical. A
numerical indicator may be based on a measured or a calculated value that reflects a
property of an INS. Examples might be the estimated probability of a major release of radionuclides to the containment obtained from a PSA or the number of intact safety barriers
maintained after a severe accident. A logical indicator is usually associated with some
necessary feature of an INS and usually is presented in form of a question. In the INPRO
areas (economics, safety, waste management, etc.) some indicators may be applicable to the
total INS, some are valid only for specific components (such as the reactor) or for specific
nuclear technologies (e.g., light water reactors), some relate to the functionality of a system
or component, and some set out measures for implementation or methods of analyses.
In addition, some indicators utilize Evaluation Parameters (EP). These parameters were
introduced to assist the INPRO assessor in determining whether the acceptance limit for an
indicator has been met. In some specific cases these evaluation parameters have their own
acceptance limits, in which case they could be called sub-indicators. An example of
evaluation parameters could be the use of parameters, such as some combination of design
simplification, improved materials, increased operating margins, increased use of passive
safety, increased redundancy, as an indicator for increasing the robustness of an INS
component relative to an existing design as a means of enhancing defence in depth.
In addition to the mathematical classification of indicators, another type of indicator, a socalled Key Indicator (KI).
The Acceptance Limit (AL) of an INPRO criterion is a target, either qualitative or
quantitative, against which the value of an indicator can be compared by the INPRO
assessor leading to a judgement of acceptability (pass/fail, good /bad, better/poorer.). In
correspondence to the two types of indicators there are also two types of acceptance limits,
numerical (for quantitative targets) and logical (for qualitative targets). Typically, a logical
AL is a positive (yes) or negative (no) answer to a question raised by the indicator.
As mentioned in the introduction to this chapter, the boundary conditions for an INS, as
assumed in a particular scenario, are expected to change with time. Thus, it is foreseeable
that some ALs might also change with time.
An example of a criterion (numerical and logical) in the area of safety (related to the
example of the user requirement regarding a major release of radioactivity discussed above)
could be the following:
Indicator: Calculated frequency F of major release of radioactive materials to the
environment
Acceptance limit: F should be less than 10-6 per unit per year or a major release should be
excluded by design.
If the calculated frequency is used, the indicator is a numerical indicator that represents the
probability for a large release and the acceptance limit is the given value of the expected
frequency of occurrence of 10-6 per unit per year. If “exclusion by design” is used, the
indicator is a logical indicator for which the acceptance limit is the answer “yes”. For some
components of the INS the assessor, e.g., technology developer, might use the calculated
frequency while for other components the assessor might use “exclusion by design.”
The relationship between a basic principle, a user requirement and a criterion, indicated by
the arrows in Figure, is as follows:
- The fulfilment of a criterion (criteria) for an INS is confirmed by the indicator(s) complying with the acceptance limit(s);
- The fulfilment of an user requirement(s) is confirmed by the fulfilment of the corresponding criterion (criteria) (bottoms up approach); and
- The fulfilment of a basic principle is achieved by meeting the related user requirement(s).
While, the sequence of an INPRO assessment is bottoms up, the logical sequence in
presenting and discussing the INPRO requirements starts with the basic principles (BP),
followed by the user requirements (UR) and finally the corresponding criteria (CR), i.e. a
top down approach. The process followed in developing and modifying the requirements is
an iterative one, involving a mixture of top-down and bottoms-up approaches.
BPs, URs and CRs have been developed during Phase 1 of INPRO for all areas of an
INS.
In preparing the various volumes of the INPRO manual it became apparent that the
statements of basic principles (BP) and user requirements (UR) set out in TECDOC–1434 were not in all cases fully consistent with the definitions given above. Where this
problem could be addressed by a small modification in wording and/or minor changes in
structure of the BPs and URs, the change was made. Thus, in the INPRO manual the
statements of basic principles and user requirement in several INPRO areas, e.g.,
infrastructure, deviate somewhat from those in TECDOC-1434. Where a significant
modification was required, the statements presented in TECDOC-1434 were retained but a
statement has been added to indicate the nature of the change contemplated. One of the main
goals of the INPRO manual has been to provide more detailed advice on the specification of
criteria. The clarification of the criteria provided in the INPRO manuals has also led to some
deviation from the information provided in TECDOC-1434.
INPRO BPs, URs, and criteria are broadly based. They represent an idealization of what is desirable taking into account both national and regional trends and what is likely to be technologically achievable. It is difficult to factor in step changes in technology, so INPRO has extrapolated current trends. Member States are free to and, indeed, in a number of INPRO areas, particularly economics and infrastructure, should specify country or region or technology specific criteria and user requirements.
See also
[ + ] Assessment Methodology | |||||
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