ML20246L486
| ML20246L486 | |
| Person / Time | |
|---|---|
| Issue date: | 12/09/1988 |
| From: | Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Jordan E Committee To Review Generic Requirements |
| Shared Package | |
| ML20245E100 | List: |
| References | |
| NUDOCS 8907180447 | |
| Download: ML20246L486 (9) | |
Text
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y DEC 9 1988 l
MEMORANDUM FOR: Edward L. Jordan, Chairman Committee to Review Generic Requirements FROM: Eric S. Beckjord, Director Office of Nuclear Regulatory Research
SUBJECT:
CRGR REVIEW OF THE MARK I CONTAINMENT PERFORMANCE IMPROVEMENT PROGRAM By December 7, 1988 memorandum, RES and NRR requested CRGR review of the Mark I containment performance improvement program and we forwarded 15 copies of the proposed Commission paper with enclosures. We have additional information which we wish CRGR to consider, as follows:
Appendix A - Backfit Analysis Memorandum from F. Gillespie, NRR, to W. Houston, RES dated December 9, 1988, with NRR comments.
In accordance with CRGR cperating procedures, we are enclosing 15 copies of the additional information for your review. For further information on this subject, please contact Leonard Soffer at x23916.
M Eric S. Beckjord, Director Office of Nuclear Regulatory Research Enclosure E Appendix A - Backfit Analysis-
- 2. Gillespie to Houston Mtmorandum Dated December 9,1988 cc: V. Stello Distribution: TMurley, FGillespie, TCox, DPersenko, JRidgely, NUDOCS, Circ File, Chron File SAIB File
- See previous concurrence 8907180447 881213 '[
PDR REVGP NPCCRGR PDR MEETING 152
[CRGR RE'!IEW 0F MAR). ICPIP]
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NAME:JRidgely :LScffer :WBeckner :WMiimers :WHouston :T5peis :EBeckjord_
FATE:12/9/88 :12/9/88 :12/9/88 :12/9/88 :12/8/88 : : 12lilV X :
OFFICIAL RECORD COPY '
A- -
MEMORANDUM FOR: Edward L. Jordan, Chairman Committee to Review Generic Requirements j l FROM: Eric 5. Beckjord, Director
. Office of Nuclear Regulatory Research l- .,
SUBJECT:
CRGR REVIEW 0F THE MARK I CONTAINMENT PERFORMANCE / l IMPROVEME!!T PROGRAM
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By December 7,1988 memorandum, RES'and NRR requested CRGR review!of the Mark I containment performance improvement program and we forwarded 15 copies of the proposed Commission paper with enclosures. We have additial information
! which we wish CRGR to consider, as follows:
1 Appendix A - Backfit Analysis Memorandum from F. Gillespie, NRR, to W. Houstan, RES dated December 9,1988, with NRR coments. /
It should be noted that the Human Factors Assessment anch of NRR is currently preparing a generic letter related to revision 4 of the Emergency Operating Procedures.
[
In accordance additional informationwithforCRGR operating your review. For fprocedures, drther information on thi subject, please contact Leonard Soffer at x2y16.
Eri S. Beckjord, Director 0 fice of Nuclear Regulatory Research Enclosure 1,, Appendix A - Backfit Analysi
- 2. Gillespie to Houston Memor hdum Dated December 9, 1988 cc: V. Stello Distribution: TMurley, FG 1espie., TCox, DPersenko, JRidgely, NUDOCS, Circ File, Chro File SAIB File
[CRGR REVIEW 0FMARK I CPIP]
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ENCLOSURE 1
. APPENDIX A BACKFIT ANALYSIS Analysis and Determination That the Recommended Safety Enhancements for Containment Performance Improvements Complies With the Backfit Rule 10 CFR 50.109 The Commission's existing regulations establish requirements for the design and testing of containment and containment cooling systems (10 CFR 50, Appendix A, General Design Criteria 50, 52, 53, 54, 55, 56, and 57) with respect to design basis accident conditions. As evidenced by the accident at TMI Unit 2, accidents could progress beyond design basis considerations and result in a severe accident. Such an accident could pose a challenge to the integrity of containment. Existing regulations do not require explicitly that nuclear power plant containments be designed to withstand the severe accident conditions.
This issue has been studied by the staff and our consultants as part of the severe accident program for the General Electric Company Boiling Water Reactors (BWRs) with Mark I containments. The BWRs with Mark I containments have been reviewed first because of the perceived susceptibility of the Mark I containment to failure based, in part, on the small containment volume of the Mark I containment design. Both deterministic and probabilistic analysis were performed to determine the dominant challenges to containment integrity and potential failure modes affecting the likelihood of core melt, reactor vessel failure, containment failure, and risk to the public health and safety. Although the nsk analysis shows that there is no undue risk to the public health and saficy, these studies show that the contribution to the overall plant risk from station blackout (TB) and loss of long-term decay heat removal capability (TW) can be significantly reduced.
The estimated benefit from implementing the proposed plant performance improvements is a reduction in the frequency of core melt due to TB and TW events and the associated risk of offsite radioactive releases. The risk reduction for the 24 operating BWR reactors with Mark I containments is estimated to be between 69,500 and 553,000 man-rem and supports the Commission's conclusion that l
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The backfit analysis is included as an appendix to this report. It is intended to be a stand alone document that minimizes the need to refer to additional documents by including sufficient detail to assess each l consideration in the back fit rule (10 CFR 50.109). Therefore, the backfit analysis repeats much of what is already included in the main body of the report.
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implementation of the proposed safety enhancements for Mark I plants provides a substantial improvement in the level of protection of the public health and safety. ,
i The cost to licensees to implement the proposed safety enhancements would j vary depending on the existing capabilities of each plant. The costs would be primarily existing for licensees equipment (1) toadditional to provide assess the plent's capabilities,(3) operational flexibility, to(2) modify j retrofit plants with additional components or systems, as necessary, to meet 1 the pro and (5) toposed capabilities, provide (4) to revise operator training relatedthe emergency to mitigating operating severe procedures ,
accidents.
The estimated total cost for the 24 BWRs with Mark I containments to provide i the proposed safety enhancements is between $48 and $176 million. The cost per reactor would be between $1.6 and $7.3 million.
The overall value-impact ratio, not including accident avoidance costs, is estimated to be between 1,449 and 3,144 man-rem averted per million dollars ,
based on a range of core melt frequencies for TW and a range of installation i costs. If the net cost, which includes the cost savings from accident i avoidance (i.e.,cleanupandrepairofonsitedamagesandreplacementpower following an accident), were used, the estimated overall value-impact ratio )
would improve slightly to between 1,570 and 3,622 man-rems averted per l million dollars. These values support proceeding with the proposed Mark I {
containment performance improvements. l The preceding quantitative value-impact analysis was one of the factors considered in evaluating the proposed improvements, but other factors also played a part in the decision-making process. Probabilistic risk assessment (PRA) studies performed for this issue have shown that station blackout s(TB) and loss of long term decay heat removal (TW) events can be significant contributors to core melt frequency, and, with consideration of the conditional containment failure probability, TB and TW events can represent an important contribution to reactor risk. In general, active systems {
required for reactor and containment heat removal are unavailable during the l postulated severe accidents. Therefore, the offsite risk is higher from a j severe accident than it is from many other accident scenarios, j l
Although there are licensing requirements and guidance directed at providing I a containment and support systems intended to contain any release of material from the reactor vessel, containment integrity may be significantly l challenged under severe accident conditions. The challenge to containment j integrity is primarily by over-pressure and over-temperature. Failure of I the containment can initiate core degradation (as in the TW sequence) or can I be the result of core degradation (as in the TB sequence).
t The estimated frequency of core melt from TB and TW events are directly proportional to the frequency of the initiating events. Estimates of TB frequency was based on the information provided in draft NUREG-1150, " Reactor 2
Risk Reference Document", for Peach Bottom Atomic Power Station, Unit 2.
I This is assumed to be a realistic estimate of the core melt frequency'for Mark I plants after the plant is in compliance witn 10 CFR 50.63, the station blackout rule. For the TW sequence, a range of frequencies was used based on the PRAs available for the Mark I plants. This range is assumed to be typical of those plants where TW is the dominant contributor to core melt, as suggested in WASH-1400.
The factors discussed above support the determination that the additional defense in-depth provided by the ability of a Mark I plant to cope with a severe accident would provide a substantial increase in the overall protection of the public health and safety, and the direct and indirect costs l of implementation are justified in view of this increased protection. The staff has considered how this backfit should be prioritized and scheduled in light of other related regulatory activities. Pursuant to 50.54(f), the licensees are to furnish, within 120 days, a proposed schedule for completing each of the proposed improvements. The equipment changes required should be installed within 30 months after the effective date of a generic letter. The procedures and training required should be implemented on a schedule reviewed and approved by the NRC. Modifications that cannot be scheduled for completion within 30 months must be justified by the licensee.
One U.S. f acility, Pilgrim, has installed a hardened vent system, but it is not yet operational.
Analysis of 10 CFR 50.109(c) Factors (1) Statement of the specific objectives that the backfit is desioned g achieve The objective of the proposed Mark I containment performance improvements is to reduce the risk of severe accidents by reducing the likelihood of core melt and by improving the ability to mitigate the consequences in the event of a severe accident. Specifically, the proposed improvements is for all BWRs with Mark I containments to enhance the reliability of the automatic depressurization system (ADS),
to provide an alternate supply of water for injection into the reactor vessel and for operation of the containment sprays, and to provide a hardened vent capability from the containment wetwell to the plant stack and to implement improved procedures and training. These modifications are to be operable during a station blackout by means of an additional power supply.
(2) General description of the activity required by the licensee or applicant in order to complete the backfit In order to comply with the proposed containment improvements, licensees will be required to Evaluate the plant's actual capabilities relative to the proposed I safety enhancements. This evaluation will include 3
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- verifying the ability of the ADS cables inside' containment to remain operable.in the anticipated environment during a severe accident
- verifying the availability of a diesel. powered water pump and the capacity of the' pump to provide low pressure cooling to the core with a depressurized reactor and to the drywell sprays during a severe accident verifying the capability of the containment vent system to l withstand the anticipated containment pressures without failing any portion of the vent path to the stack verifying the capability of the containment isolation valves to be opened and reclosed under all anticipated containment pressures and vent flow rates during severe accidents
- Determine the necessary plant modifications to comply with the proposed containment improvements, develop a scheduie for plant modifications, and submit the schedule to the NRC within 120 days from issuance of the generic letter.
- Complete necessary plant modifications within 30 months from issuance of the generic letter.
Depending on the plant's existing capability to cope with severe accidents, licensees may or may not need to backfit hardware modifications. (See item 8 of this analysis for additional discussion.)
Licensees will be required to have procedures.and training to cope with and recover from severe accidents. These procedures should conform to Revision 4 of the BWROG Emergency Procedure Guidelines.
(3) Potential change in the risk to the public from the accidental offsite release of radioactive material Implementation of the proposed BWR Mark I containment improvements is expected to result in an estimated total risk reduction to the public ranging from 69,500 to 553,000 man-rems over an assumed 20 years of remaining life for the 24 Mark I plants, based on the particular plant's TW frequency.
(4)Potentialimpactonradiolooicalexposureoffacilityemployees For the 24 operating BWRs with Mark I containments, the estimated total reduction in occupational exposure resulting from reduced core damage frequencies and associated post accident cleanup and repair activities is 1,500 man-rem. The estimated total occupational exposure for installation of the proposed improvements is between zero and 408 n.an-rem. No increase in occupational exposure is expected from c;peration and maintenance activities associated with the proposed improvements.
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(5) Installation and continuiag costs associated with the backfit, including the cost of f acility oowntime or the cost of construction delay No Mark I containments are under construction, thus there are no costs associated with construction delays. All plant modifications are expected to be capable of being made either with the plant operating or durir.g normal plant outages, thus there are no costs associated with additionel plant downtime.
The cost of the proposed improvements has been estimated to range between $1.6 and $3.2 million per plant with a best estimate of $2.0 million. For the 24 Mark I plants, this represents an industry cost range of $38.4 to $76.8 million with a best estimate of $48 million.
Pilgrim has instituted a Safety Enhancement Program which incorporated some of the recommended containment improvements. The Pilgrim costs for those elements identified as part of the containment performance program is $7.3 million. This would translate to an industry cost of $176 million.
(6) The potential safety im)act of changes in plant or operational complexity, including tie relationship to proposed and existing regulatory requirements The proposed containment improvements to be able to cope with severe accidents should not add to plant or operational complexity. The containment performance improvement (CPI) program is related to several NRC programs as the following discussion indicates.
IndividualPlantExaminations(IPE)
The IPE involves the formulation of an integrated and systematic approach to an examination of each nuclear power plant now in operation or under construction for possible significant plant-specific risk contributors that might be missed without a systematic search. The examination will pay specific attention to containment performance in striking a balance between accident prevention and consequence l mitigation. It is anticipated that the IPE program may take from three i to five years until the last plant has performed the IPE and
- incorporated the appropriate plant modifications. Since the staff has already identified cost-effective improvements that are generic to BWRs with Mark I containments, there is no need to wait for the IPE to be completed. The modifications related to the CPI program are expected to be installed in approximately 30 months.
- Improved Plant Operations (IPO)
The IPO includes consideration of the continued improvements in the Systematic Assessment of Licensee Performance (SALP) program; regular reviews by senior NRC staff managers to identify and evaluate those plants that may not be meeting NRC and industry standards of operating performance; diagnostic team inspections; improved plant Technical Specifications; improved operating procedures; expansion of the 5
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4 Emergency Operating Procedures (EOPs) to include guidance.on severe accident management strategies; industry's programs to reduce transient and other challenges to engineered safety feature systems; feedback from the IPE program of experience and improvements in operational areas, such as maintenance and training; and continued research to evaluate the sensitivity of risk to human errors, the contribution of management to the level of human errors, and the effectiveness of operational reliability methods to help identify potential problems early and prevent their occurrence. The IPO is needed to the CPI program's recommendations since we recommend improved procedures and operating training.
- Severe Accident Research Program (SARP)
The SARP was begun after the TMI-2 accident in March 1979 to provide the Commission and the NRC staff with the technical data and analytical methodology needed to eddress severe accident issues. This program has provided input to the NUREG-1150 program and to the CPI program. The results of the CPI program are not expected to affect the SARP program.
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- External Events The Commission's Severe Accident Policy Statement does not differentiate between events initiated within the plant and externally initiated events. Typically, external events have not been incorporated in the staff PRAs. Procedures for external events examinations are under development and the evaluation of external events will proceed separately. The CPI program only addresses internally initiated events and it is not anticipated that future consideration of external events will adversely affect the recommendations of the CPI program.
- Accident Management The accident management program is concerned with addressing certain preparatory and recovery measures that can be taken by the plant operating and technical staff that could prevent or significantly mitigate the consequences of a severe accident. This includes measures taken by the plant staff to 1) prevent core damage, 2) terminate the progress of core damage if it begins and retain the core within the reactor vessel, as possible, and3)finally failing)that, maintain 4 minimize containment of the consequences integrity offsite as long releases. The CPI program recommended plant enhancements wbuld provide the accident management program with additional capabilities to achieve their goals by providing improved hardware and incorporating improved training and procedures with which to deal with severe accidents.
(7) The estimated burden on the NRC associated with the backfit and the availability of such resources The estimated total cost for NRC review of industry submittals is $0.4 millon based on submittals for 24 reactors and an estimated average of 200 man-hours per reactor.
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(8) The potential impact of differences in facility type, design, or age on the relevancy and practicality of the backfit The proposed improvements are only for BWRs with Mark I containments.
All reactors and containments in the category are essentially similar and thus the recommendations are applicable to all 24 Mark I plants.
However, a survey of Mark I plants has identified that, to varying degrees, each facility may already have some of the equipment which may be used to satisfy the requirements of the CPI program. For example, a dedicated safe shutdown facility may provide the needed power and alternate water supply. Some plants may have a diesel driven water pump for the fire protection system or a diesel driven service water pump. A hardened vent pipe may already exist from the wetwell to outside of the reactor building, leaving only a small section of the vent path requiring replacement.
(9)Whetherthebackfii.isinterimorfinaland,ifinterim,the justification for imposing the backfit on an interim basis The CPI recommendations for Mark I plants is the final resolution for containment performance except as related to the liner meltthrough issue. Confirmatory research on this issue will continue, and is expected to show that use of water in the drywell will have a benefitial effect of preventing or at least delaying liner meltthrough, in addition to mitigating any consequences. The proposed improvements are not'an interim measure.
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