ML20040F074
| ML20040F074 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 02/02/1982 |
| From: | Vincent R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| References | |
| TASK-***, TASK-RR NUDOCS 8202080286 | |
| Download: ML20040F074 (9) | |
Text
o ConSumBIS Power C0mpany oonere8 offices: 212 West Michigen Avenue, Jackson, MI 49208 + (617) 788-o550
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Dennis M Crutchfield, Chief o
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Washington, DC 20555 DOCKET 50-155 - LICENSE DPR BIG ROCK POINT PLANT -
SYSTEHATIC EVALUATION PROGRAM During a meeting held on December 17, 1981 between senior iGC and SEP licensee representatives, each licensee was requested to provide an updated schedule for addressing the balance of the applicable SEP topics and recommendations regarding the conduct of the Integrated Assessments at the conclusion of the program. provides what we believe is a complete list of topics requiring additional work for Big Rock Point, and gives expected completion dates for identified Consumers Power Company activities. As you will note, no attempt has been made to provide expected completion dates for reviews of NRC evalua-tions which have not yet been issued. We will, however, attempt to be as responsive as possible in providing our comments after receipt of the draf t SERs.
With respect to the Integrated Assessment process, we believe that the primary vehicle for determining the true safety significance of each difference from current criteria should be the Big Rock Point Probabilistic Risk Assessment (PRA). The PRA will not only allow a more objective assessment of the effect of each difference on overall plant risk, but it also offers the advantage of allowing true cost-benefit analyses of potential ba<.kfit items.
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Big Rock Point Plant SytematicEvaluation Program February 2,1982 therefore proposed that Consumers Power Company perform the Integrated Assessment for Big Rock Point using the PRA. A description of our approach is provided as Attachment 2 to this letter. We will be happy to discuss this with you in more detail at your convenience.
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Robert A Vincent Staff Licensing Engineer CC Administrator, Region III, USNRC NRC Resident Inspector-Big Rock Point Attachments - 7 pages i
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Big Rock Point Plant Expected SEP Topic Schedule j
CP Co Action Items Expected Topic CP Co Action Submission Date II-2.A Submit additional comments.
3/1/82 II-2.C Submit SAR 4/15/82 II-3.A Review and comment on SER when Unknown II-3.B issued by NRC II-3.B.1 II-3.C III-I Review and ccmment on SER when Unknown issued by NRC III-2 Submit SAR 6/82 i
l III-3.A Submit SAR af ter SER for II-3. A, Unknown 3.B, 3.B.1 and 3.C issued by NRC III-4.A Submit SAR 3/15/82 III-4.B Submit SAR Approx. 6/82 III-4.C Submit SAR 5/1/82 III-5.A Submit SAR 5/1/82 III-5.B Submit SAR 4/1/82 III-6 Submit analysis results 6/1/82 III-7.B Review and comment on SER when Unknown issued by NRC III-10.A Review and comment on NRC SER 3/1/82 V-10.B Review and comment on NRC SER 3/15/82 V-11.B Review and comment on NRC SER 3/15/82 VI-1 Submit SAR 4/1/82 VI-2.D Review and comment on SER when Unknown VI-3 issued by NRC VI Review and comment on SER when Unknown issued by NRC nu0282-000lbl42
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Attachm5nt 2 SYSTEMATIC EVALUATION PROGRAM PLAN FOR THE INTEGRATED ASSESSMENT OF BIG ROCK POINT USING THE PROBABILISITC RISK ASSESSMENT 1.
INTRODUCTION The Systematic Evaluation Program (SEP) was initiated by the U.S. Nuclear Regulatory Commission (NRC) to review the design of older operating nuclear power plants against current safety criteria and regulations. The primary objectives of the program were (1) to document how each plant compares with current criteria on significant safety issues, and provide a rationale for acceptable departures from those criteria; and (2) to provide a capability to make integrated and balanced backfit decisions when departures were deemed unacceptable.
A list of 137 significant safety topics was developed from existing generic safety issues and concerns. Some of these issues were sub-sequently deleted frem the program s cope because the topics were not applicable or were being generically reviewed as Unresolved Safety Issues (for example:
Anticipated Transients without Scram) under the Three Mile Island HRC Action Plan, etc.
Each topic that remains has been or currently is being reviewed to determine whether or not plant design is consistent with current criteria.
For Big Rock Point this review is being conducted as described in Section 2.
When deviations from current criteria can not be resolved at the topic evaluation state, an " integrated assessment" procedure has been proposed to determine the safety significance of taeb Item and the need for backfitting at the Plant.
This procedure is subjective in nature in that it relies heavily on individual judgment.
In itself, this is not necessarily undesirable, but it does mean that the quality of the final product is very dependent on-the background, training and experience of the people making those judgments.
It is recognized that overall plant risk considerations will be addressed in light of IREP and other risk assessments performed by licensees, but the fact that these risk assessments are not specific to the SEP plants under review will somewhat limit their applicability. This is particularly true for the unique design of Big hock Point.
The ideal situation would be to have a risk assessment for each SEP plant with which objective determinations of safety significance and meaningful cost-benefit analyses of potential backfits could be performed.
In the case of Big Rock Point, this ideal is attainable.
In a letter dated February 22, 1980, Consumers Power Company proposed to develop a Big Rock Point Probabilistic Risk Assessment (PRA) to be used for the evaluation of existing plant risk, as well as to provide a tool for the evaluation of new issues that may arise in the future.
The Director of NRR, by letter dated October 14, 1980, acknowledged the program as a "valusble tool for providing insight into the identification of significant contributors to risk".
As a result, the PRA for Big Rock Point was completed and submitted to the NRC on March 31, 1981.
Consumers Power Company hereby proposes that the Big Rock Point PEA be u ed as the basis for the SEP integrated assessment and for the determination oi the need for backfits at Big Rock Point.
It is the belief of CPCo that safety issues of sufficient importance to justify capital or operational expenditures beyond those currently planned need to be justified in the light of the PRA.
Car recommended approach for using the PRA in this role begins with recognition of the fact that CPCo has, based on the PRA, suggested a number of design and procedural modifications to reduce plant risk to what we believe to be an acceptable level. Part of the recommeded program is a Continuing Risk Revised 1/26/81
2 Management Program which will assure that the effects of plant aging and new issues resulting from operational experience or improved understanding of important phenomena do not degrade plant safety below an acceptable level, as defined in the AIF recommended safety goals and in the draft NRC safety goal.
The PRA-based integrated assessment vill, therefore, assess the effect of unresolved SEP issues on safety of the plant in both its pre-modified and post-modified states. Where sigaificant improvemente seem to be possible by addressing the SEP issue for the plant ir its post-modified state, a more detailed investigation of the cost effectiveness of alternative design or procedural modifications to be implemented vill be based on their assessed cost effectiveness.
The remainder of this plan presents our recommended approach.
2.
TOPIC EVALUATIOUS For each of the significant safety topics a topic review has been or is being performed by one of the following methods.
In the first method, the NRC staff reviews the plant design as it relates to the topic, and issues a draft Safety Evaluation Report (SER) which identifies any differences between ERP and current criteria.
CPCo then reviews the draft SER for accuracy, and identifies any plant design features which may have been overlooked and which may affect the ultimate resolution of the topic. Follow-ing receipt of CPCo comments the NRC staff reviews the comments, incorporates any necessary changes, and issues a final SER.
In the alternate approach, CPCo submits a safety analysis report (SAR) in which the features of the plant relating to the topic are described, and the degree of compliance with the criteria is assessed. Also included in the SAR may be an evaluation of topic importance in terms of risk. This evaluation may include an explicit discussion of the PRA conclusion about the topic, or a subjective dicussion of the importance of the topic to the PRA results. Where a topic is clearly not important to risk, that conclusion and the basis there-fore is documented in the SAR and no further evaluation is performed.
Sufficiently detailed deterministic evaluations would be performed, however, for each topic which is clearly applicable and risk significant, and which has not been addressed by the PRA or other recent activities. Using the SAR as g basis, the NRC staff would issue the final topic SER.
3 INITIAL SCREENING OF SEP ISSUES As an initial step in the PRA based integrated assessment of SEP issues, the final SER's will be reviewed to allow initial categorization. Figure 1 depicts this initial categorization process. As shown, SER's which dismiss the topic will be reviewed and, contingent on concurrences by CPCo, eliminated from further consideration. A second set of issues may not be directly addressable by the PRt..
These vill be screened out and an approach for resolving them defined.
Issues in this category may include fundamental questions regarding the design basis of equipment or about the adequacy of phy3ical models and assumptions made in accident analyses.
A third set of issues are those covered by the PRA as it currently stands.
For these issues the conclusions of the PRA relative to the issue vill be stated and substanticted, and suggested design or procedural modifications developed in the PRA to deal with the issue vill be discussed.
3 The fourth and final set of issues, those which can be addra ssed by the PRA but which have not yet been adequately treated, will involve the most significant level of effort to assess.
This set may be subdivided into two sub-sets: one for snich it is not clear that the necessary information for evaluation exists, and one for which the existing information base vill support a PRA-based evaluation. Figure 1 notes various types of issues which may fit into this final set.
The SEP issues in this final set will be evaluated using the general approach outlined in the remainder of this letter.
h.
RAIIKIIIG OF SEP ISSUCS Following issuance of a final SEP on each of the significant safety topics, and the initial classification cf issues as discussed above, the integrated assessment procedure vill be performed.
As a first step in the integrated assessment it is proposed that each of the identified differences or findings be ranked against one another, as well as against the risk outliers identified in the PRA, by their contribution to overall plant risk. A sim.41ar procedure was followed in the PRA (see Section 7 of the Main Report) in which risk outliers were defined as features or functions of the pJant which contribute significantly to the total core damage frequency. For the integrated assessment it is proposed to rank the SEP issues in terms of contribution to risk (i.e. man-rem) rather than of contribution to core damage frequency as was done in the PRA.
This will allow direct value-impact analyses to be performed.
In order to rank the issues it will be necessary to follow one of two courses: 1) To first propose conceptual plant design or procedural modifications which address each finding, and second, evaluate the amount of risk reduction derived from the change.
It is expected that many of the more significant SEP findings will have already been identified as risk outliers by the PRA, and thus information needed to rank the finding vill already exist in the PRA report.
Or 2) To evaluate the effect of complete resolution of the issue on the risk presented by BRP.
For some SEP issues it may be necessary to develop several conceptual modifications. This was done in the PRA (see Section 7.2 of the Main Report) in an effort to determine the most cost effective means of addressing the risk outlier.
In addition, for some risk outliers the most effective modification in terms of risk reduction potential was not obvious at first, and thus the analyst made use of the risk models to determine an optimal solution.
For each issue, the effect of the proposeu,lant modification (or complete 2 colution of the issue) on overcl1 plant risk will be determined. An er4uple of he method by which this vill be done can be found in Appendix XI to tu.
PRA report.
It is important to determine the overall effect of each modification, rather than only assessing its effect on the SEP finding or risk outlier it was intended to address, so as not to either overstate or understate its true value.
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CLASSIFICATION OF SEP FINDINGS SEP findings in classes III and IV as described previously (also see Figure 1) will be classified as either significant (i.e. contributing greater than a small percentage (1%) of the overall risk of the plant in its pre-modified state) or not significant. Significant SEP findings which have not been considered fully by the PRA (i.e. class IV issues) will be further evaluated in the value-impact analyses described in the following section.
6.
VALUE-IMPACT ANALYSIS For the rignificant SEP findings, if any, a value-impact analysis will be performed using scoping estimates of costs for engineering, materials and construction associated with implementation of the conceptual design modifi-cations.
The value of the proposed modifications will be estimated in a manner similar to that described in Section 7 of the PRA Main Report.
It will be necessary to consider the proposed modifications in carefully selected groups so as to yield maximum risk reduction at the lowest cost.
Diffez ent groupings of the proposed modifications addressing SEP findings and PRA risk outliers may be evaluated, because the value of a particular modification may be somewhat dependant on the other risk reduction measures that are taken.
7 DISPOSITION OF SIGNIFICANT SEP FINDINGS Based on the value-impset analysis, cost-effective plant modifications can be selected for implementation.
It is proposed that plant modifications be selected for implementation on the basis of the ratio of their cost-to-risk reduction potential. As an example, only those proposed modifications with cost-to-benefit ratios of less than $X/ man-rem would be candidates for implementation, where X likely would fall between $100 and $1000 and would be the subject of further discussion between CPCo and the NRC Staff.
8.
SCHEDULE It is expected that performance of the 1:RA based integrated assessment would require approximately three to six months.
This period would start at the point when essentially all final topic evaluations have been issued by the NBC.
FIGURE 1 SCREENIIG OF SEP ISSUES USIIG THE FRA CLASS I Raview to assure egreement then Issues judged Evaluate SEP dismist, from e
unimportant issues further consider-ction b.y SER's CLASS II CLASS III kpphdIc$ kiEeSe lIsues -g---
be RA nc us on d scuss are related to physical effe veness of suggested PRA understanding of system design mods. (from PRA) or engineering adequacy of equipment design.)
CLASS IV Need for fbrther evaluation by PRA Y
, Included as assumptions in PRA-1mEvaluate effect of l
(Env. Qual) variations in assumptions (Prioritize actions) e Incomplete treatment of issue in PRA (Seismic, tornado, high m>Sxpand treatment to define energy line break effects on risk significance and sen-cable trays).
sitivity to assumptions, e Treatment in continuing risk program 9 Potential but undefinable
-a1> (Example: Leak detection effects on initiator frequency effect on LOCA initiator or severity frequency and on the relative frequency of various sizes of LOCA event Assess the u ility of syste which currently exist or alternative use of existinE systems as compared with existing systems in existin, uses.
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