ML20203G694
| ML20203G694 | |
| Person / Time | |
|---|---|
| Issue date: | 02/20/1998 |
| From: | Shirley Ann Jackson, The Chairman NRC COMMISSION (OCM) |
| To: | Diaz N, Dicus G, Mcgaffigan E NRC COMMISSION (OCM) |
| References | |
| COMSAJ-98-003, COMSAJ-98-3, NUDOCS 9803030044 | |
| Download: ML20203G694 (6) | |
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UNITED Si TEii L
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WASHINGTON, D.c 2055ko001 COMSAJ-98-003 I
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February 20, 1998 RTIEASED TO THE PDR ah,nr ku dab initials l
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MEMORANDUM T0:
Comissioner Dieus Comissioner Diaz Commissioner McGaftigan Shirley Ann Jackson j 7-A FROM:
SUBJECT:
DISCUSSION ON RISK-INFORMEC. PERFORMANCE-BASED
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REGULATION Attached is a draft paper that attempts to define and/or clarify several concepts related to risk-informed, performance-based regulation. The put e
of such a paper is two-fold:
(1) to clear up misconceptions that may Li resulted from varying uses 6f these terms; and (2) to clarify that these concepts can be applied across the full range of NRC regulatory activities (i.e., rulemaking, licensing, inspection, assessment, enforcement, etc.) for both reactor and materials applications.
An advanced draft of this paper was recently forwarded to you for comment.
My staff is in the process of reviewing and incorporating comments received from Commissioner Dicus.
However, in the interest of expediting this effort we request your review and approval through this C0!1.
SECY please track.
Attachment:
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Risk Informed Performance Based Reaulation The NRC has established its regulatory requirements, in both reactor and materials applications, to ensure that "no undue risk to public health and safety" results from licensed uses of Atomic Energy Act materials.
Based on advances in risk assessment methodology and the accumulation of experience.
the Commission is advocating certain changes to the development and implementation of its regulations, through the use of risk-informed.
performance-based approaches. The Probabilistic Risk Assessment (PRA) Policy Statement (60 FR 42622. August 16. 1995) formalized the CommissioW s s
commitment to risk-informed regulation through the expandeo use of PRA.
The PRA Policy Statement states, in part. "The use of FRA technology should be increased in all regulatory matters to the extant supported by the state of the art in PRA methods and data, and in a manner that complements the NRC's i
deterministic approach and supportr. the NRC's traditional defense-in-depth philosophy."
g To understand and apply the commitment expressed in this policy statement it is important that the NRC. the regulated community, and the public at large b
have a common understanding of the terms and concepts involved; en awareness of how these concepts (in both reactor and materials arenas) are to be applied to NRC rulemaking, licensing, inspection. assessment, enforcement, and other decision-making; and an appreciation of the transitional period in which the agency and the industry currently operate.
1.
Iraditional Anoroach:
The current body of NRC regulations is braely baset on a " deterministic" approach--that is, requiremen'.s have been devised based on a defined set of causes and effects (derived both empirically and predictively) associated with a given use of licensed material (2.g., in a reactor plant or a nuclear medicine application).
This approach employs the use of safety margins. operating experience, accident analysis, and qualitative assessments of risk, relying heavily on the applicatica of the " defense-in-depth" philosophy) Since this approach attempts to account for the predicted severity of adverse effects. it might be considered, at some level. " risk-informed."
However, as explained below. the c^quisition of more event data and the
' Defense-in depth is an eierent of the NRC's Safety Philosophy that employs successive compensatory measures to prevent accidents or mitigate damage if a malfunct;on or accident occurs at a nuclear facility. The defense-bt-depth phi'osophy ensures th3t sdfety will not be wholly dependent on any single element of the design, construction, mal.itenance, or operation of a nuclear facility. Redundancy (the use of multiple identical trains of a common system) and diversity (the use of unlike methods to avoid susceptibility to tommon-mode failure) in the design of protettive features are examples of defense-in-depth strateg.es-a3 are extensive quality assurance programs. Operator training programs. ongoing testing and maintenance program;. and NRC regulatory oversight. The net effect of incorporating defense-in-depth into design construction, maintenance. and operation is that the system in question tends to be more tolerant of failures.
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increasing sophistication of certain risk assessment methods (e.g.,
Probabilistic Risk Assessment (PRA). Integrated Safety Assessment (ISA),
and Performance / sessment (PA)) provides the opportunity to enhance this traditional approach by improvirg the incorporation of risk l
insights.
i 2.
Areas for Imorovemont: While the traditional approach to regulation has been successful in ensuring adequate r.otection (i.e., "no uMue risk to public health and safety") in the use of nuclear materials, several opportunities for enhancement exist. The body of regulations has evolved in response to evolving experience: therefore, some degree of
" patch-work" has resulted--leading to the appearance of inconsistency or Jnevenness in emphosis. Given t h broad spectrum of equipment and ictivities covered. the,egulations can be strengthened to ensure that they are focused on the most risk-significant equipment and activities.
I and to ensure consistent consideration of a coherent framework for regulatory decision-making. The " risk-informed" and " risk-infrw ed, performance-based" approaches to reguldtion described below, il properly applied, would provide such a coherent framework.
3.
Risk and Risk Assenment:
For the purposes of this paper, the term
" risk" is used to express the combination of the consequences of an j
undesirable event and its probability of occurrence.
The most fundamental expressions of " risk" relate directly to public health effects, as in the Commission's Safety Goals.
Other expressions of
" risk" include core damage frequency (CDF)2 and large early rehase frequency (LERF).3 The term " risk insights." as used here, rtfers to the results and findings that come from risk assessments.
For reactors, these insights include such things as the identification of dominant accident seauences, core damage frequency containment failure probability, changes in CDF uid LERF. dominant risk contributors, and importance measures.
A risk essessment is a systematic method for assessing system performance, including human performance. to understar,d likely outcomes, sensitivities. areas of iniportance, system interactions, and areas of 2CDF is the frequency of the combinations of initiating events, hardware failures. and human errors leading to core uncovery with reflooding of the cora not imminently expected.
'LERF 15 the frequency of those accidents leading to significait. unmitigated releases from containment ir, a time frame prior to effective evacuation of the close-In population such that there is a potential for early health effects.
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3 uncertainty.
The risk insights yielded by these risk assessment techniques have been incorporated successfully into numerous regulatory activities, and have proven to be a valuable complement to traditional engineering approaches. Given the current body of event data and the improvements in some risk-assessment methods. risk assessment i
methodologies can be incorporated more explicitly into the regulatory process in a manner that will improve both the efficiency and the ef fectiveness of current regulatory requirements.'
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" Risk-Based"_:
A " risk based" approach to regulatory decision-making _is an approach that relies exclusively on risk assessment results.
Note L
that the Commission does noi endorse, nor has it ever endorsed, a " risk-based" approach to regulatory decision making.
5.
" Risk-Informed": A " risk-informed" approach to regulatory decision-making represents a philoscphy to be used in all regulatory matters whereby risk insights are considered together with other factors, such as the basis for current regulations, engineering analysis and judgment, the defense-in-depth philosophy, and preserving adequate safety margins.
These integrated elements at a used to establish requirements that focus licensee and regulatory attention on design and operational issues commensurate with t hir importance to public health and safety.
'G sk assessments also can be used to quantify the relationship between uncertainty and defense-in-depth. The magnitude of a single calculated risk number cannot be used to eliminate safety barriers without due consideration of uncertainty. Redundant and d verse protective features serve as multiple barriers against catastrophic events. Typicall.. each layer of a multi-tarrier system (whether human or nardware) will have much highe" failure rates than a single stand alone barrier. Each layer also generally has an associated operrtional database that can be used to provide some level of confidence in the performance of that particular barrier. Relaxations based on risk information Wuld likely involve situations where one barrier of a multi-barrier system is believed to have a much higher availability than others, suggesting that the requiremen" on the others may be Unnecessary.
Note, however, that th? single barrier system with higher availability may not have an asscciated experience database that would provide the desired confidence in system performance. Consequently, any argument ?1 rd..'ve barriers, if based on risk assessments.
must be accompanied by a scrutable and rig - methodology for addressing uncertainty.
Note, in addition. that the term " multiple barriers" has a slightly rtifferent meaning in the context of radioactive waste disposal systems. specifically. a waste disposal system must include multiple natural and engineered barriers (typically paesive in nature) so that unavailability is not a particular concern. Also, mu?tlple barriers in a waste disposal system normally are not redandant and it is possible to have the " top" event with one or even all barriers functional.
e 4
A ' risk-informed' approach enhances the traditional approach by:
(a) allowing explicit consideration of a broader set of potential challenoes to safety. (u, providing a logical neans for prioritizing these challenges based on risk significance, operating experience, and/or engineering judgment, and (c) facilitating consideration of a broader set of resources to defend against these challenges.
A ' risk-informed' appre i can be used to focus regulatory attention on those areas most important to public health and sety by considering risk in a more coherent and comprehensive manner. Where appropriate, a risk-informed regulatory approach can be used to reduce unnecessary conservatism in deterministic approaches, or can be used to identify arees with insufficient conservatism and provide the bases for additional requirements or regulatory actions.
Note that a risk-informed regulation can be either prescriptive or performance-based. A prescriptive requirement specif"s particular l
features, actions, or programmatic elements to be int.
9d in the design l
or process, as the means for achieving a desired objeu.1ve. A performance-based requirement specifies measurable (or calculable) outco,nes (i.e., performance resu~.s) to be meo. but provides more flexibility to the licensee as to the means of meeting those outcomes.
6.
' Performance-Based': A perfe'mance-based approach is an approach that establishes performance and results as the primary basis for regulatory decision-making, and incorporates the following attributes:
(1) measurable parameters to monitor, with clearly defined, objective criteria against which to assess plant and licensee performance: (2) licensee flexibility in determining how to meet the established performance criteria that will encourage and reward improved operations:
and (3) a framework in which the failure to meet a performance criterion, while undrsirable, will not in and of itself constitute or result in adverse consequences.
A performance-based approach can be implemented without the use of risk insights.
Such an approach would require that objective performance criteria be based on deterministic safety analysis and performance history.
This approach would still provide flexibility to the licensee in determining how to meet the performance criteria.
Establishing objective performance criteria for performance monitoring may not be feasible for some applications and, in such cases, a performance-based
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approach would not be feasible As applied to inspection, a performance _-based approach tends to temphasize results (e.g.. does the pump work?) over process and method (e.g., was the maintenance procedure well-written?).
Note that a
-performance-based approach to inspection does not supplant-or displace-
-the need for compliance with NRC requirements. nor does-it displace the-need for enforcement action, as appropriate, when non-compliance L
- occurs 6
-As applied to lice _nsee assessment a performance-bated appcoach focuses on a licensee's actual performance results (i.e., desired outcomes),
rather than on predicted improvements or self-assessments (i.e..
-outputs).
In the broadest sense, a performance-based ap.oroach to regulatory oversight will focus more attention and NRC resources on those licensees whose-performance is less than optimal.
7.
" Risk-Informed. Performance-Based":.A risk-informed,_ performance based apprcach to regulatory decision-making combines the " risk-informad" and
" performance-based" elements discussed in Items S-and 6,'above, and:
applies thesel concepts to NRC rulemaking, licensing, inspection, assessment, enforcement, and other decision-making.
Stated' succinctly, risk-informed. performance based regulation is an approach in which risk insights, engineering analysis and judgment, and performance history are used, when-_ feasible -(1) to develop measurable and/or calculable-parameters for monitoring system and licensee performance. (2)'to establish objective criteria for evaluating performance, and (3) to focus on the results as the primary basis of regulatory decision-making.
' Substantial differences exist among various reactor and materials applications (including the approximately 40 activities, systems, and devices that use or addrs the
- dispo;al of nuclear material *,).-and alternative attributes should be censidered in many cases. For example, the degree of accident potential, the level of hazard, and the complexity of the application varies greatly between low-activity sealed sources and large
' fuel cycle facilities. In addition the data available for determining compliance with performance-based regulations varies from actual personnel monitoring data (as in radiography applications) to predictions of geologic performance over 10.000 years. These and other differences should be considered whe1 defining specific attributes for using a
-performance based regulatory approach over a range of applications.
'Not every aspect of licensed activities can or should be inspected using this approach.. For example, if a licensee is unsuccessful in meeting the criteria defined by a performance-based regulation, the inspector should focus on the licensee's process and method, to understand the root cause of the breakdown in perfonnance. and to understand how future poor performance may be avoided.