ML20028B941
| ML20028B941 | |
| Person / Time | |
|---|---|
| Issue date: | 12/31/1982 |
| From: | NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | |
| Shared Package | |
| ML19255G438 | List: |
| References | |
| NUDOCS 8212280502 | |
| Download: ML20028B941 (14) | |
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ACTION PLAN TO IMPLEMENT THE COMMISSION'S SAFETY GOAL POLICYkTkiF5ENT DECEMB.ER 1982 v.:-
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. 4;..AC4-ION PLAN T0. IMPLEMENT THE.
COMMISSION'S SAFETY GOAL POLICY STATEMENT TABLE OF CONTENTS f.EL' P u rp o s e.....................$.....................'...........
1 1.
1 II.
Scope.'.......................................................
2 III. General Approach to Be U s ed.......'............................
IV.
Proposed Use in Regulatory Decision Process..................
5 Eid V.
. Assessment of Results at End of T. rial-Use P r o.............
8 Appendix A - Highlights of. Future Staff Actions.................
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Purpose This document provides the action plan to implement the Commission's fety gear ~piility'.Stemelit'tliat'hus 'beTn'issand-for trial use.
The
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sa purpose of the plan is to outline (1) the scope of regulatory issues that may be as'sessed using the safety goals, (2) the general approach to be used in developing the data and information needed to make the assessments and to improve the usefulness of the safety goals in regulation and licensing in the future, (3) a description of how the safety goals will be used as a factor in arriving at regulatory decir; ions, and (4) hoi the results of.using the safety goals will be
. _ _ _.... _. assessed at the end of the trial period.
II.
Scope
{
- The qualitative safety goals and quantitative design objectives
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contained in the Commission's Policy Statement will not be used in the licensing process during the trial period.
However, the NRC'has used and plans to continue.using probabilistic risk assessments (PRA).to
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,"'better understand the risks of various safety issues.
The quantitative safety goals will be used, where the PRA methodology is generally accepted, to examine existing regulatory. requirements, evaluate proposed new regulatory requirements, establish research priorities, prioritize and resolve generic safety issues, and evaluate the. relative safety t
importance of issues as they arise.
These analyses will also provide information regarding the timing of implementation of any new requirements and the Irelative merits of alternative approaches.
f Certain proposed new generic requirements to'be reviewed by the Committee to Review Generic Requirements (CRGR) will be assessed using the safety goals design objectives as one perspective for decision making.
These issues will include the following:
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(1)
(2)
Pressurized thermal shock of pressure vessels (USI A-49) (NRR)
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(3)
Siting policy or rulemaking, after new radiological source terms are available (RES)
(4)
Severe accident policy or rulemaking (RES/NRR)
(5)
Station Blackout (USI A-44) (NRR)
__, 6)_ _ Decay Heat _ Removal,,(USI A-45) (NRR)
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(7)
Reconsideration of Emergency Response (RES):
The safety goal design objectives. Will also be used during the trial period as one factor in reassessin'~ selected existing requirements.'
g Examples of such issues which roay be re-examined are the reTiability criteria for the auxiliary.feedwater system of PWRs and the requirement
- ' to combine seismic and 1.0CA loads in the design of structural and mechanical components and their supports.
Also, when new information on'the radiological source terms from severe accidents becomes available in 1983, the impact on safety goal comparisons will be asse'ssed.
III. General Acoroach to Be Used i
The design objectives in the policy statement include the risks from routine emissions, normally expected transients and low consequenc'e accidents, design bash accidents, and accidents which might melt the Compliance with Appendix I to Part 50 assures' that the risks from core.
routineemissionsaresmal]jtherefore,theyneednotbeanalyzedeither generically or on a plantypecific basis to demonstrate conformance with l
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the safety goals.
Also, compliance with current regulations (principally Parts 20, 50, and 100) generally provides adequate protection against the risks from anticipated transients and low 5
'conseq'uencMici3ehCa'if welf Tis 8erign 5 asis Rcidents; therefore, these need not be analyzed to demonstrate conformance with the safety I
goals.
Thus, 'to implement the safety goal policy statement during the trial period, this action plan will focus on the risks from accidents involving potent,ial core-melt.
An early step in implementinh the policy statement' will be for the Office of Nuclear Regislatory Research.(RES) to coliect available information on PRA studies.and prepare ~a reference, document tha_t describes the current status of knowledge conce'ning the risks of plants r
licensed in the U.S..
It is ess'ential that a reference document be s
prepared and receive peer review so that the. staff, licensees, and public have a common base of information on the dominant contributors to the probability of core-melt and to the public risk due to radiatiori from serious nuclear a'ccidents,'the strengths and weaknesser of current plant designs and operations, and the usefulness of PRA and the safety
" yoals in assessing such strengths and weaknesses.
This reference document will assess the uncertainties associated with estimates of core-melt probab'ilities and radiological consequences.and will attempt to provide guidelines on how these uncertainties should be '
treated.
It will also assess the uncertainties associated with making relative risk assessments compared to absolute risk assessments; and it -
will address the oncfrtainties in assessing the risks from external
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events (seismic and flood), and from fire, compared to the uncertainties of assessing risks from internal accident initiators.(equipment failure and operator errors).
The reference document will include an assessment of procedures used for these PRA studies and their impact on the validity of the results, as
I well as a discussion of when it is appropriate to consider the risks from external events such as earthquakes and floods, the likely magnitude of such risks, and how one should evaluate such risks in light tf the'1argrUncirta'iiitTes'inv51v'dr -It7111 risu identify those areas
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of plant design that appear to be most amenable to possible improvement, including insights that have been gained with regard to the desired and achievable reliability of-systems and components important to safety, s
In parallel with the development of this reference document,' the staff will begin using the safety goals quantitative des'ign objectives in some of the areas identifiind in Section II.to begin developing a base of hands-on experience._In implementing the benefit-cost guideline, the
$1,000 per person-rem averted will be in 1983 dollars, and it will be.
modified to reflect general inf1'ation in the future.
Both the benefits (reduction in estimated public exposure) and.the' costs will be assessed for the remaining lifetime of the plants.
The staff will continue assessing the reliability of systems and compon.ents important to safety.
Reliability criteria have already been
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- specified for auxiliary feedwater systems and diesel generators for plants in the licensing process,.but these will have to be tested against th'e safety goal design objectives and.perhaps adjusted.. Reliability '
allocations to systems or components affecting core-melt pr'obability will have to be measured against the design' objectives with due consider-ation given to the differences between designs that utilize similar components or systems but which may have differing risk importance.
Implementation of-such' reliability criteria typically will make use of simplified reliability or probabilistic risk analyses.
They will consider reliabilities that are' technically achievable in a cost-effecti/e manner.
The reliability criteria will be single-valued aiming points that are accompanied by upper and lower bounds of acceptability.
This approach will permit safety tradeoffs between systems, depending on their risk importar.ce in specific plant designs.
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l Because of the present uncertainties in analyzing the risk from external l
events, care will have to be taken with regard to any apportionment of l
the design objectives between external and all other (internal) accident initia'tcrs.'thiThub[eTt wiil'b5' addressed in'the reference document.
Substantial research is now underway to' develop more effective techniques to ' analyze the probability of core-melt and the risk from external events.
When this is completed, PRA will be used to determine generically whether the risk attributable to external hazards is large enough to warrant routine consideration in safety goal decisions.
PRAs will be performe'd using realistic assumptions, and the estimates normally will be base'd on median. values after propagating uncertainty.
distributions.
Also, the analyses will include'as good an estimate as.
is feasible of the magnitude and nature of uncertainties,' including differences between median and mean estimates, together with sensitivity analy'ses for certain parameters important to risk.
It is the intention that conservatisms will be explicitly expressed in the decision rationale,
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rather than be buried in the risk analyses.
"One way to improve the consistency of PRA results is to provide some reasonable assurance that analysts follow equivalent procedures,.make similar~ assumptions, treat phenomena consistently, and utilize a common data base.
NRC has developed reasonably prescriptive guida'nce on how to..
conduct a PRA, drawing upon the Integrated Reliability Evaluation '
Program (IREP) and the work of the ANS/IEEE.
Such standardization is highly desirable for effective use of the safety goal design b
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objectives.
IV.
Procesed Use in Reculatory Decision Process '
In evaluating proposed new regulatory requirements and assessing the need for regulatory action on safety issues that arise, the staff will i
i use the safety goals as one of the factors in the decision process.
The weight to be-given the safety goal will depend on many considerations.
One important consideration will be the quality of the PRA information,
including the source of the analysis, the methods and data used, and 'the extent of peer review it has received.
Insofar as possible, the staff i
members most familiar with the PRA and its limitations will be consulted in the' decivilin $rbcis's This'stdf' input wi1Pprovide an essential perspective to those who must consider the PRA information and weigh its importance in-making a decision. --
Other factors in making decisions will include the uncertainties
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surrounding the PRA analyses,_ engineering judgment, the acceptability.
of safety tradeoffs implicit in the decision, and'the applicable l
. regulatory requiremen'ts.
The staff believes that the above, coupled with the scrutiny given PRAs by the. industry, the NRC staff, NRC...
management,.the ACRS, and other experts Ed11 provide sufficient controls
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to avoid abuse of the use of PR s and safety goa1s in regulation; but this judgment will have to be further evaluated during the trial-use period.
Because of the uncertainties inherent in PRAs one must be cautious in making. absolute comparisons.between a risk estimatenfor a. plant and one
- '?.of the safety goal design objectives.
If, for example, such a comparison indicates that a design objective is not met, one would 0
ex'pect the next step would be to ex' amine the underlying technical It could be that such an examination would reveal' that an.
reasons.
existing regulatory. requirement is not met,'i.n which case the appropriate re'gul,atory action would be to~ focus on the improvements in the plant needed to meet the regulatory requirement.
In other cases it may reveal a gap in ou'r requirements, in which case appropriate actions may be needed to amend the regulations, depending on the safety benefits and the costs of the proposed actions.
The timing of any corrective
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actions, if needed, would depend on factors such as the estimated magnitude of the risks involved, the need for power, the number of plants involved, the cost of replacement power, and.he available industry and NRC t
resources.
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It is expected that the initial focus in using the safety goal in the near future will be on the design objective on core-melt frequency, and a
estimates of public risk would normally only be performed if the I: ore-m'eTt design'$B%tTve'is' exdeetied, ifr'a rilR=important accident sequence is dominant.
However, the impbrtance of mitigating the consequences o'f a core-melt accident is fully recognized, and the staff will continue to emphasize features such as containment and emergency planning as integral parts of the defense-in-depth concept.
Where there is a reasonable udgment that the pub 1'ic risk and core-melt frequency design objectives actually are met for current plants, benefit-cost evaluations should not be performed to justify plant design modifications that further reduce risk.
This judgment will include
- consideration of the quality of'the PRA analyses} used in the assessments.
Where significant, occupational exp5's'ures would also be a consideration
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in any decision whethe*r to make' safety improvements.
Such considerations would. include any i.ncreased exposures accrued during
."plantmodificationsandanyincrementalincreases(ordecreases) subsequently required to mainfain,the plant.
However, it is not clear e whether occupational exposures would be given the same weight in decisions as would public exposures.
One consideration that.is important is that the occupational exposure incurred as a result of any '
imposed new requirement is a real impact with a small uncertainty band, whereas averted public exposures are calculated probabilistic numbers withlargeuncertainhbands.'
The paramount thought in making decisions Using PRAs and the safety goals is that one must be sensitive to the " bottom-line risk" syndrome.
The principal benefit of PRA, considering the present state-of-the-art, is to identify strengths and weaknessey in plant design and operation, not to calculate accurate, absolute risk numbers.
Therefore, the primary application of PPA information in deciding generic safety A
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.m issues during the trial period will be to use the results and insights gained from the spectrum of PRA analyses done to date, which will be summarized,in the reference document.
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i V.
Assessment of Results at End of Trial-tTse Period
~ At the"end of~ the' trial ~use period 'the staff will assess t e information h
gathered on PRAs contained in the reference document, together with the hands-on experience gained in. implementing the safety goals, to make recommendations to the Commission regarding any ch'anges'in the safety goals and their use in regulation or licensing.
This assessment will.
-include:
1.
A comparison of etisting p1' ant-specific PRA's with the design
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objectives.
2.
A discussion of situations where PRAs and the design objectives provided a useful perspecf.ive for decisions, and where~their use was not very beneficial.
ye-The impact of any change 3 in, source. terin asstamptions on the safe'ty 3.
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goals, including whether the design objectives should be changed.
4.
An evaluation of the need for proposed' guidelines as to actions to be taken when one or more plants are' estimated to exceed one or both of the public risk design objectives 'and/or the c' ore-melt design objective; For example, sh'ould operating levels or limits be established; and, if so, what should they be?
Judgments regarding the methodology for containment performance 5.
assessment and whather a containment performance design objective would be useful.
If so, what should be the recommended design l
c.jective(s)?
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The influence of occupational exposures or other factors on decisions made during the trial-use period.
7.
Judgmeiti reghrTing tWmitth6dtilogy7 hat thculd be used to perform PRAs to enhance their use in the regulatory process.
8.
For any future plant-specific applications, an evaluation of alternatives as to how conformance with the individual risk guideline should be assessed for situations where no one lives within one mile of the site boundary.-
'9.
Whether a single monetary value of averted person-rem is an appro-priate and useful way to implement the benkfit-cost guideline. 'If not, what might be more appropriate?
Careful attention will be paid to management of the various activities during the trial-use period.
Toward this end the staff will do the following:
W Establish appropriate tasks and milestones (Ref. Appendix A) in the' FYB3-85 EDO and Commissi6n. Program Planning and Guidance documents and in office Operating Plans.
Establish a Steering Group which will include, as a minimum, '
management level representatives from the EDO, NRR, RES, IE, ELD, and OPE.
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Provide appropriate reports to the Commission including the '
reference document, an assessment of substantive public comments received, and recommendations on any mid-course corrections that appear warranted.
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t APPENDIX A HichTiohts 'of FtruNe MifT'X'et. ions ' ** ' - '
- d The following summaYizes the action items required to iinplement the. safety goals"ahd develop improved technical implementation guidance during the trial Information gathered during the trial use period will 'be use period.
evaluated by the staff to assist iD any subsequent recommendations to the
. Commission regarding the future role of PRA.or the safety goals in regulation or licensing.
1.
Prepare a reference document that evaluates existing PRAs Early FY-84
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assess the dominant acciderit sequences; identify to:
and rank safety systems and components as to,their risk importance; evaluate how the risksifrom external events should be weighed in the decision piecess; estimate the
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magnitude, direction,' and risk
- significance of uncer-tainti,es; and assess lessons learned with regard to
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" strengths and weaknesses of various methodologies and procedures.
(RES)
. 2.
Provide appropriate reports to the Commission regarding, FY-83-85 implementation of the safety goal, such as the reference document, evaluation of public comments, and any recommended mid-course corrections that might a'ppear to-be warranted.
(E00) -
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FY-83-85 Improve the quality and review of PRAs by developing a j
3.
review plan for PRAs, consensus on the methodology 'for assessing the performance of all types of containments, and guidance on the assessment of the risks of external events.
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Implement the safety goals:
Prioritize generic safety issues (NRR)
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Evaluate proposed new requirements'that are FY-83-85 c
amena:le lo assessment by PRA (RES/NRR)
Prioritize research in areas amenable to FY-83-85 c.
FY-83-85 ~.
d.
. Develop and begin to implement a plan to assess existing requirements to determine whether some aspects need changing (RES) e Begin to develop risk-based reliability. criteria.
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'for systems and components most important to safety (NRR/RES) f.
Begin to develop a methodology to prioritize FY-83-84
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selected reactor inspection procedures and to assist decision-making on the issuance of circulars, bulletins, and orders related to generic issues (IE) 5.
kakerecommendationsattheendofthetrialuseperiod for the future use of safety goals in regulation and licensing, including policy changes based on the experience gained [ f rther guidance regarding implemen-tation; any action guidelines felt to be warranted to assist decision-making as to whether new req 0irements should be implemented or existing requirements waived, and the timing of implementation of new requirements; application of the safety goals to operating reactors e
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and licensing, e.g., the use of operating limits; and the effect of new developments, such as revised radiological source terms, on the implementation of the sa'f e'ty -'foiil s7 T500T ' ' ~ "'"'
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