ML20055E303
| ML20055E303 | |
| Person / Time | |
|---|---|
| Site: | FitzPatrick  |
| Issue date: | 06/15/1990 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Brons J POWER AUTHORITY OF THE STATE OF NEW YORK (NEW YORK |
| References | |
| GL-89-16, TAC-74868, NUDOCS 9007110273 | |
| Download: ML20055E303 (47) | |
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n umiso STATES NUCLEAR REGULATORY COMMIS$10N W ASHINGT ON, 0. C. 20666 l
. *%....+l! Oune 15, 1990 ;
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'l I Docket No. 00 333 '
. I Mr.' John C. Brons Executive Vice President - Nuclear Generation i Power Authority of the State of New York 1 123 Main Street ,
White. Plains,.New York 10601
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Dear Mr.- Brons:
SUBJECT:
STAFF'S BACKFIT ANALYSES FOR JAMES A. FITZPATRICK NUCLEAR I POWER PLANT REGARDING INSTALLATION OF A HARDENED WETWELL
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VENT (GENERICLETTER89-16)(TACNO.74868) j 1
In SECY 89-017, " Mark 1 Containment Performance Improvement Program " of January 23, 1989, thestaffdemonstratedthathardenedwetwellventIng capabilities at Mark I containments would prevent the majority of severe i accident sequences involvir:p loss of decay heat removal capability (TW I sequences) from resulting in core melt. The staff also demonstrated that
. venting through a hardened vent path from suppression pool airspace would significantly mitigate the risks to public health and safety, because substantial. amounts of fission products released by core melt would be trapped in the suppression pool and would not be available for release to the environ- i ment. Some benefits are also expected because of the prevention of severe J accident sequences other than TW sequences from resulting in core melt. Based the staff informed the Commission that the on.the genericanalyses in of installation SECY 89-017,d vent capabilities at Mark I containments hardene ,
would provide significant added benefits resulting from a reduction of severe l accident risks to public health and safety.
On July ll,1989, the Comission responded to the staff recomendations in SECY 89-017 and directed the staff to implement, on a generic basis, the installationofhardenedventcapabilitiesatboilingwaterreactors(BWRs) with Mark I containments. Accordingly, on Se stember 1,1989, the staff !
issued Generic Letter 89-16 (GL 89 16). In tiat letter, the staff urged
'the affected licensees to voluntarily install hardened vent capabilities at '
their Mark I containments using the provisions of the Commission's rules in 10 CFR 50.59. If the licensees chose not to install the hardened vent capability on a voluntary basis, the staff requested in GL 89-16 that the licensees provide their plant-specific estimates of costs of installation of hardened vent capabilities. The licensees were informed that the staff would use the cost data to perform plant-specific backfit analyses and to determine if hardened vent installations could be imposed as backfIts in accordance with the Comission's backfit rule in 10 CFR 50.109.
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Mr. John C. Brons - 2 June 15, '990 By letter of October 27, 1989, you responded to Gl. 8916 indicating that you had decided not to commit to install hardened vent capabilities on a voluntary basis. You also provided the staff with plant-specific cost estimates for modifications at the James A. FitzPatrick Nuclear Power Plant (FitzPatrick).
Following the receipt of your October 27, 1989 letter, the staff initiated plant-specific backfit analyses for FitzPatrick. the staff In its analyses,ff used the plant-specific cost estimates that you provided. The sta estimated the benefits of venting by determining the reductions in core damage frequencies (CDFs) for only the TW sequences. The benefits were calculated y using the results of the probabilistic risk assessments (PRAs) for BWR$ with Mark I containments similar to FitzPatrick's. The staff then adjusted the analyses to I account for recent advances in the PRA methodology (NUREG 1150). The results !
of the staff's analyses showed that for TW sequences alone the overall CDF for '
FitzPatrick can be reduced by 4.5 E-5 per reactor year. The analyses were adjusted to account for the power level of FitzPatrick and the density of population surrounding the FitzPatrick site. Thestaffhascalculatedthat for TW sequences alone, the operation of the vent would avert the expected radiological exposure to public by 65.5 man-rem per reactor year. Using 25 years of remaining plant life for FitzPatrick, the staff has estimated an I averted radiological population exposure of 2408 man rem ser million dollars.
The preceding results of the staff analyses demonstrate t1st hardened vent l capabilities would provide significant benefits in the expected reduction in j radiological exposure risks posed by TW sequences.
The staff has also calculated the other averted costs that would be associated with severe accidents involving TW sequences to clean the site surroundings and to replace the lost power. The averted costs of cleaning the site surroundings and replacing power, would be $786,000. Assuming that the averted costs of cleaning the site and replacing the power would offset the cost of the modification, the modification costs would be fully offset by the benefits of averted costs.
The staff has considered but not quantified the reduction in risks posed by (1)severeaccidentsotherthanTWsequences,and(2)scrubbingofthefission products in the suppression pool for accident sequences that result in significant damage to the core. These benefits provide added incentives for installation of a hardened vent capability at FitzPatrick.
Based on the preceding quantitative and qualitative discussions, the staff believes that there will be a substantial additional increase in protection to the public health and safety if a hardened vent capability is implemented at Fitzpatrick. Therefore, the staff has concluded that the backfit is justified for FitzPatrick. A copy of the staff's supporting analyses for FitzPatrick is enclosed for your information.
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Mr. John C. Brons June 15, 1990 In your letter dated October 27,.1989, you raised several questions regarding the staff's analyses in SECY 89-017. The staff's responses to your questions are also included in Appendix B of the enclosure, in light of the staff's backfit analyses, the staff urges that you reconsider your decision and comit to install a hardened vent capability at FitzPatrick.
You are requested to inform the staff of your intent within 30 days of recei)t of this letter. You may implement your comitment under the provisions of tie Commission's rules in 10 CFR 50.59, provided that the modifications are in place by January 1993. In the absence of such a comitment, the staff intends to pursue the imposition of this backfit under the provisions of the Comission's'backfit rule in 10 CFR 50.109.
Sincerely, Original signed by Thomas E. Murley, Director Office of Nuclear Reactor Regulation
Enclosure:
Plant-Specific Backfit Analyses for FitzPatrick cc w/ enclosure:
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+ Docket filot"* AThadani NRC/ Local 90Rs PDI-2 Reac'ng File TMurley/FM raglia JPartlow WRussell SVarga BBoger CVogan DLaBarge RCapra MThadani OGC EJordan ACRS(10)
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W ell 90 JGPartlo 06 /90 06 u ey
/90 M%y i* 1 P
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'r. f+r. Jphn C. Brons James A. FitzPatrick Nuclear .
., Power Authority of the State of New York Porer Plant )
I cc:
Mr. Gerald C. Goldstein Ms. Donna Ross Assistant General Counsel New (ork State Energy Office Power Authority of the State 2 Empire State Plaza of New York 16th Floor 1633 Broadway Albany, New York 1&223 New York, New York 10019 .
Resteent inspector's Office Regional Administrator, Region I !
U. S. Nuclear Regulatory Comission U. S. Nuclear Regulatory Comission l Post Office Box 136 475 Allendale Road !
Lycoming, New York 13093 King of Prussia, Pennsylvania 19406 l Mr. William Fernandez Mr. A. Klausman Resident Manager Senior Vice President - Appraisal James A. Fitzpatrick Nuclear and Compliance Services Power Plant Power Authority of the State i Post Office Box 41 of New York
Mr. J. A. Gray, Jr. Mr. George Wilverding, Manager Director Nuclear Licensing BWR Nuclear Safety Evaluation -l Power Authority of the State Power Authority of the State I of New York of New York l 123 Main Street 123 Main Street l White Plains, New York 10601 White Plains, New York 10601 l Supervisor fir. R. E. Beedle Town of Scriba Vice President Nuclear Support R. D. #4 Power Authority of the State Oswego, New York 13126 of New York i 123 Main Street tir. J. P. Bayne, President Power Authority of the State ;
of New York flr. S. S. Zulla 1633 Broadway- Vice President Nuclear Engineering New York, New York 10019 Power Authority of the State of New York 123 Main Street Mr. Richard Patch White Plains, New York 10601 Quality Assurance Superintendent -
James A. FitzPatrick Nuclear Power Plant Post Office Box 41 Mr. William Josiger, Vice President Lycoming, New York 13093 Operations and Maintenance Power Authority of the State of New York 123 Main Street '
Charlie Donaldson, Esquire White Plains, New York 10601 Assistant Attorney General ;
New York Department of Law 120 Broadway New York, New York 10271 t
n 1
J Plant-specific Analysis for the Fit Patrick Nuclear Power Plant, Regarding Installation of a Hardened Vent 4
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TABLI OF CONTENTS 1.0 Background ................................................... 1 2.0 Discussion .................................................... 2 2.1 Safety Benefits ............................................ 2 2.2 Reduction in Core Damage Frequency and Public Risk ......... 4 2.2.1 Plant Similarity Assessment .......................... 4 2.2.2 Reduction in Core Damage Frequency .................. 5 2.2.3 Risk Reduction ...................................... 6 2 . 3 Cost- Bene f it Ana lys i s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2 . 3 .1 Cos t Es t ima t i on . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.3.2 Value-Impact Assessment ............................. 7 2.4 Alternatives considered and Impacts on Other Programs ...... 8 2.5 Environmental Assessment ................................... 8 3.0 conclusions and Recommendations .............................. 9 3.1 Rationale for the Recommendation ........................... 9 4.0 References .................................................. 11 Appendix A Regulatory Analysis on the Backfit of Hardened Vent Appendix B Response to comments in NYPA Letter of October 27, 1989
Plant-Specific Analysis for the PitzPatrick Nuclear Power Plant, Regarding Installation of a Hardened Vent 1.0 Backaround In SECY-87-297 (Reference 1), dated December 8, 1987, the Nuclear Regulatory Commission (NRC) staff presented to the Commission its program plan to evaluate generic severe accident containment vulnerabilities in a program entitled the Containment Performance Improvement (CPI) program. Thi staff began this effort with the premise that there may be generic severe accident challenges to each light water reactor (URR) containment type that should be assessed to determine whether additional regulatory guidance or requirements concerning needed containment features is warranted. The premise that such assessments are needed is based on the relatively large uncertainty in the ability of some LRR containments (for example, Mark I) to successfully survive some severe accident challenges, as indicated by RUREG-1150, dated June 1989 (Reference 2). This effort is integrated closely with the program for Individual Plant Examination (IPE) and is intended to focus on resolving hardware and procedural issues concerning generic containment challenges. In SECY-89-017 (Reference 3), dated January 23, 1989, the staff presented its findings concerning the Mark I CPI program to the Commission. One of the improvements that the staff recommended was the installation of a hardened vent capability.
The staff concluded that venting, if properly implemented, can significantly reduce plant risk. This vent capability has long been recognized as important in reducing risk caused by loss of long-term docay heat removal events. Controlled venting can prevent the long-term over-pressurization and eventual failure of containment, the failure of Emergency Core cooling System (ECCS) pumps caused by inadequate not positive suction head, and the re-closure of the valves in the Automatic Depressurization System (ADS). Venting of the containment is currently included in the emergency operating procedures for boiling water reactors (BWRs) . A vent path using existing containment penetrations currently exists in all Mark I plants. This vent path generally consists of a system of sheet metal ductwork that has a low design pressure of only a few psi. Venting under high-pressure conditions created either before or after core melt may fail this ductwork, release the containment atmosphere into
.the reactor building, and potentially contaminate or damage equipment needed for accident recovery. In addition, with the existing hardware and procedures at some plents, it may not be possible to open or to close the vant valves for some accident scenarios.
Therefore, venting through a sheet metal ductwork path, as currently implemented at some Mark I plants, is likely to hamper or complicate post-accident recovery activities, and is, therefore, viewed by the staff as reducing-the safety benefit. A hardened pipe vant capable
I of withstanding the anticipated pressure loading of a severe accident would eliminate this disadvantage.
The Commission concurred with the staff's position and directed the Otaff on July 11, 1989 (Reference 4) to begin imposing a hardened vent capability on a plant-specific basis for each BWR with a Mark I containment. For liccasees who, on their own initiative, elect to incorporate this plar.t improvement, the staff was directed to consider installation of a hardened vent under the provisions of 10 CFR 50.59. For the other licensees who do not intend to install a hardened vent voluntarily, the staff was to perform a plant-specific backfit analys4.s for each of these Mark I plants to evaluate the 6fficacy of requiring the installation of hardened vents.
The staf f issued Generic Letter (GL) 89-16 dated September 1, 1989 (Reference inform them5)ofto BWR the licensees direction givenwith Mark by the I containments:
Commission (1) tothe regarding hardened vent issue, (2) to provide them with a generic cost estimate for the installation of a hardened vent and (3) to request that each licensee provide notification of its plan for addressing resolution of this issue. Moreover, the staff encouraged licensees to implement the design changes to install the hardened vent. For those plants not electing to voluntarily install hardened vents, the staff requested in GL 89-16 that the licensees provide a cost estimate for installation of the hardened vent. In response to the Commission's directives, the staff developed a program to meet the objectives of the Commission's directive. This program plan contains the following five tasks: (1) cost estimation, (2) plant similarity assessment (3) cost-benefit analysis, (4) environmental assessment, and (5) imposition of requirements.
2.0 Discussion The purpose of this report is to document the results of the plant-specific backfit analysis performed by the staff for the FitzPatrick Nuclear Power Plant. This analysis complies with the backfit rule in 10 CFR 50.109 (Reference 6) and includes an assessment of the safety benefits, an estimate of the reduction in core damage frequency and public risk, and a cost-benefit analysis. From the recults of this analysis, the staff concludes that the installation of a hardened vent capability will substantially increase public safety and that the results of the cost-benefit analysis support the implementation of the capability.
2.1 Safety Benefits The major benefit of a hardened vent is the reduction of both the core damage frequency and public risks. Probabilistic Risk Assessment (PRA) studies for BWRs indicate that accidents initiated by transients dominate the total core damage frequency (CDF) in severe accident sequences. The principal accident sequences for BWRs consist-of Loss of Long-Term Decay Heat Removal (TW), Station 4
4 Blackout (SBO), and Anticipated Transient Without scram (ATWS) . The Reactor Safety Study (WASH-1400) (Reference 7) indicated that TW is 3 the dominant accident sequence causing core damage at the Peach l Bottom Atomic Power Station. Turther, draft NUREG-ll50 (Reference 2) indicates that SBo is the dominant contributor to core damage .
frequency at Peach Bottom. At peach Bottom, it was estimated that l the TW frequency has been greatly reduced because of the successful I implementation of containment venting procedures. This study indicates that venting, if properly implemented, can significantly increase cafety. j In SECY 89-017, the staff concluded on a generic basis for Mark I plants that the proposed hardened vent capability would provide cnhanced plant capabilities with regard to both accident prevention cnd mitigation. A core melt, combined with reactor vessel rupture end containment failure, would release significant amounts of fission products to the environment. The addition of a hardened vent (1) prevents the majority of IJss of long-term decay heat removal capability sequences (TW) from resulting in core melt, and (2) citigates the consequences of residual sequences involving core melt where venting through the suppression pool is found necessary. The -
TW sequences are initiated by transient events and are followed by failure of long-term decay heat removal; the containment fails from 3 cvarpressurization and causes the subsequent core melt. The installation of a hardened-vent will increase the survivability of containment, reduce the likelihood of a core melt from TW sequences, cnd therefore reduce the risks to the public. For other sequences where core melt occurs before containment failure, venting could be offective in delaying containment failure and in mitighting the release of fission products because venting through the suppression pool would provide significant scrubbing of particulate and volatile releases.
In a BWR, containment venting is currently included in the emergency cperating procedures. The existing vent path generally consists of ductwork ranging in pressure capability down to design pressure of only a few psi for most Mark I plants. The low design-pressure ductwork is inadequate for accommodating the high containment pressure following a severe accident. consequently, venting under cevere accident conditions could result in failure of the ductwork and a direct release of radioactivity into the reactor building. The discharge of high-temperature gares over an extended period of time cay threaten the availability or performance of safety-related equipatet. If substantial fuel damage has occurred, the discharge of hydrogen could cause hydrogen burns (or detonations) inside the reactor building. Electrical cables, motor operators on valves, relays, and control room components may fail under these onvironmental conditions. Adverse environmantal conditions would complicate entry into the reactor building. This environment of high temperature and perhaps radiation could hamper recovery efforts by preventing personnel from entering into the reactor building if cystems needed to terminate the accident need repair. As a result,
1 when relying on'the existing ductwork, the benefits of containment !
! ; venting are significantly uncertain. Therefore, hardening the vent i path to withstand-the anticipated pressure loading during a severe i accident would eliminate this disadvantage while retaining all the benefits of containment venting.
L Because of the reduced core melt frequency, reduced fissio'n product ,
releases, and possible reduction or elimination of a significant J containment failure mode, the staff concluded that the safety benefits of venting are significant, and further improvement can be .
ochieved by installing hardened vents. In Reference 8, the staff l cstimated the benefits in the reduction in CDF and in offsite risk, which are discussed in the following sections. l 2.2 Reduction in Core Damaae Fresuenev and Public Risk j 1
To estimate the plant-specific reduction in CDF, all Mark I plants j
.were categorized into several groups based on the similarity of the i design features that are important to the accident sequences that )
could be affected by the installation of a hardened vent. In performing the analysis, the staff used existing Mark I PRAs along with the plant similarity assessment to estimate the reduction in CDF for each group of plants. The analysis includes only the change in the core melt frequency for the TW sequence.
2.2.1 Plant similarity Assessment In draft NUREG/CR-5225 (Reference 9), the three accident sequences that were identified as being affected by venting aret (1) Loss of Long-Tern Decay Heat Removal (TW), (2) Anticipated Transient Without Scram (ATWS), and (3) Station Blackout (SBO) . Among these sequences, the addition of a hardened vent was found to produce the greatest reduction in core damage frequency (CDF) through its effect on TW coquences In the TW sequence, failure to remove decay heat
'following a transient will cause the gradual pressurization of the containment. The containment may fail from overpressurization and cubsequent?.y may lead to a core melt. In this sequence, venting can ,
be used te allow the removal of long-term decay heat from the j containneat through pool boiling and therefore, reduce the likelihood of conte Anment failure and subsequent: core melt. The design features ;
important to this sequence are the systems used for decay heat ,
rencval and containment cooling. l The reduction in CDF for the TW sequence of each Mark I plant resulting from the installation of the hardened vent was estimated by.
the staff in Reference 8. To account for similarity in design, all Mark I plants were grouped according to the design of their decay heat removal'and containment cooling systems - factors important in ossessing the frequency of TW sequences. In determining the groups
.by examining individual plant features in simplified piping and instrument diagrams, the staff studied the differences between the RHR systems, isolation condensers, power conversion system, and
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COrvice water systems for all Mark I plants. In addition, the staff l Ctudied the available PRAs and failure probabilities of related
- components to identify any major differences and similarities in tOrms of CDF affected-by the hardened vent capability. After careful ,
Otudy of the available PRAs, the staff categorized the Mark I plants into the following'four groupst .
(1) Plants with a residual heat removal (RHR) system consisting of two trains, with two RHR heat exchangers and two RHR pumps per ;
train, (2)LPlants with an RHR consisting of two trains, with one RHR heat ,
exchanger and two RHR pumps per train, l (3) Plants with an RHR consisting of two trains, with one RHR heat j exchanger and one RHR pump per train, and (4) Plants with isolation condensors. ,
- 2.2.2 Reduction in Core Damaae Fremuency To estimate the reduction-in CDF from the installation of a hardened vent capability, the staff looked into the sequences that require failure of containment cooling for core damage, and assumed that ,
i cddition of a hardened vent would reduce these sequerces by 90 ;
percent. The estimates of CDF reduction conservatively consider only ;
the TW sequences, and therefore, the benefits for the SB0 and ATWS L
coquences are not included.
! For FitzPatrick, the CDF was estimated using the PRA results of a '
L plant with similar design features. To be consistent with the L casumptions used in NUREG-1150, the staff incorporated several i changes into the referenced PRA. These changes included the generic data used and the treatment of recovery. ,
i The following are the principal changes to the referenced PRA study i
- 1. The referenced PRA study used a value of 0.5 per year for loss of main feedwater frequency (TiB) and did not consider any other way of losing the power conversion system (PCS). The !
initiator of T T 8, loss of PCS or of main feedwater leading o
to-loss of PCs,, 3has a frequency of 2.3 per year in the present study as. opposed to the value of 0.5 per year in the referenced PRA study. ,
, - 2.- The referenced PRA study did not give credit for recovery of
- l. loss of offsite power in the TW sequences. The present study
! did so.
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- 3. The probability. of nonrecovery of the power conversior, system
- was assumed to be 0.16 in 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in the referenced PRA L study, while it was 0.01 in NUREG-1150 study.
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- 4. The component data and the data for common cause failures were made consistent with NUREG-1150 generic data.
- 5. Certain common cause failures that were not included in theIn referenced PRA study were included in the present study.
particular, the common cause failure of the RMR service water outlet valves for heat exchanger A (MOV-89A) and for heat exchanger B (MOV-89B) was included. The joint failure of these valves was included in the referenced PRA study, but the failure was treated as if they were independent.
- 6. Loss of an AC or DC bus coupled with failure of the service water outlet valve for the heat exchanger in the opposite RHR loop appears to be a valid cutsat, but was not included in the referenced PRA study. This cutset was included in the present study. A cutset, consisting of loss of an AC or DC bus coupled with a service water inlet valve for the heat exchanger in the opposite loop failing closed, was included in the referenced PRA study but not in the present study. The reason for not including this cutset was its lower probability.
- 7. The referenced PRA study did not consider transients with two or three stuck-open relief valves, while the present study does consider this transient.
With these changes, the staff calculated that venting would produce a reduction in CDF of 4.5E-5 per reactor year. More detailed descriptions of the analysis are given in Reference 8.
2.2.3 Risk Reduction Installation of a hardened vent will reduce the CDF and will result in a reduction in the population dose that is associated with the TW sequences. The estimate of the reduction in population dose for Fit Patrick was calculated by multiplying the reduction in CDF estimated for FitzPatrick by a scaling factor to convert the Peach
. Bottom population dose to the FitzPatrick population dose. The scaling factor was obtained from NUREG/CR-2723 (Reference 10) for FitzPatrick plant-specific reactor power and population density. The Peach Bottom population dose from TW sequences was derived using the insights.from NUREG-1150. The resulting reduction in the population dose for FitzPatrick due to the reduction in CDF for TW sequences was estimated to be 1.46E6 man-rem. The averted population dose for FitzPatrick was calculated by multiplying the reduction in CDF by 1.46E6 man-rem to give 6$.5 man-rem per reactor year. For the 25 years of operation remaining, the estimated total averted dose is 1638 man-rem. In addition, consideration of a likely 20-year operating life extension will increase the estimated total averted dose to 2948 man-rem.
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, i The averted occupational health risk resulting from the installation ;
cf'the proposed hardened vent system is discussed and calculated in 50ction 4.1.2.2 of Appendix A. The estimated occupational risk.is 1 l
,, cpproximately one to two percent of the public health risk and is not I
CCnsidered to be a significant contributor. Therefore, the
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occupational health exposures are not further considered in the cost- . ;
benefit analysis.- t 2.3 cost-manafit Analysis C
The method used'to calculate the cost-benefit ratio is described in
' NUREG/CR-3568 (Reference 11), and the plant-specific data were ;
considered. The staff obtained plent-specific cost estimates i provided by the licensee from the response to Generic Letter (GL) 89- ?
l 16 and used the risk-reduction data discussed above in Section 2.2.3 to calculate the value-impact ratio in man-rem saved per million dollars.
l 2.3.1 cost Estimation .i i
GL 89-16 requested licensees to provide the staff with plant-specific cost estimates for installing a hardened vent. In response to GL 89- )'
' 16, all Mark I licensees except four (with five plants) indicated that they intend to install the hardened vent under the provisions of 10 CFR 50.59.
- FitsPatrick is one of the five Mark I plants. The Power Authority of 1 the State of New York (the licensee) has decided not to voluntarily 1 install the hardened vent capability. By letter dated october 27, i i
1989 (Reference 12), the licensee of FitzPatrick responded to GL 89-16 with a cost' estimate of $680,000 for the installation of a i hardened vent, and incremental costs of $70,000 for an AC-independent j 1
power source.
l2.3.2 Value-Innact Assessment ;
The value-impact ratio is calculated in the regulatory analysis 1 (Appendix A) using the method described in NUREG/CR-3568 (Reference l
- 11) to support the backfit decision. The benefits to public risk p reduction in man-rem were calculated in Section 2.2.3. The averted population dose for FitzPatrick was calculated in Section 2.2.3 to be 65.5 man-rem per reactor year. For the 25 years of operation L
remaining, the estimated total averted man-rem is 1638. The cost of installation of the hardened vent capability was estimated in Section. l 2.3.1 as $680,000. The value-impact ratio, not including the averted j
cnsite cost, is calculated to be 2408 man-rem saved per million l dollars.
Thriaverted cost associated with prevention and mitigation. of an I ac:ident can be discussed as five separate costs: replacement power, c7eanup, onsite occupational health impacts, offsite health impacts, i
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. s end.onsite property damage. The details of each of these items are i discussed in Appendix A section 4.1.2.2. If the savings of $786,578
?) ritsPatrick from accident. avoidance (cleanup, repair of onsite ,
d: mages, and replacement power) were included, the overall value- l itpact ratio would be -15366 man-rem saved par million dollars. The 1 n:gative number indicates that the averted costs exceed the {
-installation costs, which means that it is economically cost- 1 offective. Consideration of a likely 20-year operating life cxtension will increase the averted population dose to 2948 man-rem.
2.4 Alternatives considered and innacts on other Programs other alternatives considered and their associated value-impact' ratios are discussed in Section 3.0 and 4.0 of the Regulatory-Analysis'in Appendix A, Regulatory Analysis. The effect of the cddition of'the hardened vent capability on other requirements 1 including IPE, Improved Plant Operations (IPO), Severe Accident R: search Program (SARP), External Events, and Accident Management are
-discussed in Section 4.2'of Appendix A. A summary of the compliance to the backfit rule-(10 CFR 50.109(c)) is also included in Attachment 1 to Appendix A.
2.5- Environmental Assessment The staff performed a generic environmental assessment (EA) cancerning the installation of the hardened vant at Mark I plants.
C:ncurrent with this plant-specific analysis, a draft EA is being c nt out for public comments. In the draft EA, the staff concluded !
i that the installation of a hardened vent capability will have no' oignificant radiological or non-radiological impact on the environment. l The installation of the hardened vent capability will prevent and !
L oitigate. severe accidents.- During normal plant operations or design- J b sis accidents, the hardened vent will not be used, and therefore, I will not. result in any changes in amounts of radioactivity released i i to.the atmosphere from the plant. Venting during severe accidents will reduce the CDF and will reduce the radiological environmental risks. For venting sequences, the hardened vent connected to the plant stack could reduce dose consequences more effectively by cpproximately a factor of two than venting through the ductwork. '
c This reduction'is due to a greater effectiveness of atmospheric L dispersion resulting from controlled elevated release compared to an uncontrolled ground level release from ductwork. Furthermore,
- H v:nting through the suppression pool would provide scrubbing of non-noble-gas fission products with an effective decontamination factor l' ef about 100. The addition of a hardened vent will greatly reduce lthe occupational doses for personnel that need to enter and work in the reactor building and that could be exposed to the containment Cnvironment.
The staff has concluded that this generic EA applies to FitzPatrick j f
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. N cnd the installation of the hardened vent will, therefore, reduce the l dose consequences and will not result in an adverse environmental [
impact. Plant-specific design features will have an effect on the j degree of the environmental benefits, but not on the conclusion '
Concerning no significant environmental impact.
conclusions and Recommendations 3.0 Based on the safety benefits discussed in Sections 2.1, 2.2, and 2.3 I for FitzPatrick and in SECY 89-017 for generic Mark I plants and Cupported by the plant-specific cost-benefit analysis, the-staff l believes that the installation of a hardened watwell vent at
- FitsPatrick is warranted.
3.1 Rationale for the Recommandation .
In:SECY 89-017, the staff concluded on a generic basis for Mark I .
plants that the proposed hardened vent capability would provide ,
cnhanced plant capabilities with regard to both accident prevention and mitigation. The addition of a hardened vent (1) prevents the '
tajority of TW sequences from resulting in core melt, and (2) citigates the consequences of residual sequences involving core melt ;
where venting through the suppression pool is found to be necessary.
In TW sequences, the contajnment fails before the core melt occurs; therefore, significant releases could result. A core molt, o~mbined with a reactor vessel and containment failure, would release ,
oignificant amounts of fission products to the environment. The curvivability of the containment, which acts as the last barrier for on uncontrolled release of radiation, would increase with venting. l The: installation of a hardened vent greatly reduces the-likelihood of ;
o core melt from TW sequences and therefore reduces the risks to the $
public. For other sequences where core melt is predicted, venting i could be effectivo in delaying containment failure and in mitigating the release of fission products. Although. venting of the containment .
is currently included in BWR maargency operating procedures, it generally uses ductwork with a low design pressure. Venting under ,
high-pressure severe accident conditions could fail this ductwork, release tho' containment atmosphere into the reactor building, and
' damage equipment, or contaminate equipment needed for accident recovery. Venting through this ductwork will probably hamper or complicate post-accident recovery activities, and is therefore viewed Cs reducing the safety benefit. The installation of a reliable i hardened wetwell vent allows for controlled venting through a path with significant scrubbing of fission products to the plant stack and would prevent damage to equipment needed for accident recovery.
With the installation of the hardened vent capability, the staff cstimated that the total plant CDF for FitzPatrick can be reduced by 4.5E-5 per reactor year because of the reduction in the probability of TW sequences. Implementation of the proposed hardened vent todification will significantly reduce the total risk to the health and safety of the public. The averted population dose of 65.5 man-
_ _ . _ _ _ _ . _ ~ --
l r:m per reactor year was calculated for FitzPatrick from the installation of hardened vent capability. For 25 years of remaining cperating life the total averted population dose would be 1638 man-r n, and the value-impact ratio, not including the averted costs,
.w;uld be 2408 man-rem averted per million dollars. If the averted c:st associated with an accident is included, the calculated value-icpact ratio for FitzPatrich is -15366 man-rem saved per million dollars. Because the value-impact ratio is defined as the ratio of the averted population dose and the cost differential between the installation of the hardened vent and the averted cost, the negative number indicates that the averted costs exceed the installation c sts. Thus, at FitzPatrick the installation cost is justified even when considering the economic benefit alone without considering the cafety benefit. In addition, consideration of a likely 20-year cperating life extension will increase the total averted population dtse to 2948 man-rem, which demonstrates additional benefit for the installation of the hardened vent capability. Additional benefits of not quantified, include cource term reduction and the delay l V in nting,inment conta failure for some of the scenarios that lead to core colt.
Based on both the qualitative and quantitative benefits discussed horein and the supporting plant-specific cost-benefit analysis, the l Otaff believes that there will be a substantial increase in the cverall protection of the public health and safety by implementing the hardened vent capability for FitzPatrick. Therefore, the staff believes that this backfit is justified, l
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References !
4.0
'1. SECY-87-297, U.S. NRC, " Mark I Containment Performance Program Plan," V. Stello to NRC commissioners, December 8, 1987.
o 2. NUREG-1150, Second Draft, U.S. NRC, " Severe Acciden't Risks: An l Assessment for Five U.S. Nuclear Power Plants," June 1989.
- 3. SECY-89-017, U.S. NRC, " Mark I containment Performance Improvement Program, " V. Stello to NRC Commissioners, January L' 23, 1989.
l l 4. Memorandum from S. J. Chilk to V. Stallo, "SECY-89-017 - Mark I containment Performance Improvement Program," July 11, 1989.
- 5. U.S. NRC, Generic Letter 89-16, " Installation of a Hardened Wetwell Vent," September 1, 1989. ,
- 6. Backfit Rule, Code of Federal Regulation, 10 CFR 50.109.
l 7. WASH-2400, U.S. NRC " Reactor Safety Study," October 1975.
- 8. Memorandum-from Brian W. Sheron to Ashok C. Thadani, October 19, 1989, " Reduction in Risk From the Addition of Hardened Vents in BWR Mark I Reactors."
- 9. NUREG/CR-5225, draft, "An Overview of Boiling Water Reactor Mark I containment Venting Risk Implications," October 1988.
- 10. NUREG/CR-2723, " Estimates of the Financial Consequences of Nuclear Power Reactor Accidents," September 1982.
- 11. NUREG/CR-3568, "A Handbook for Value-Impact Assessment,"
December 1983.
I.,
- 12. Letter'From John C. Brons (New York Pouer Authority) to U.S.
.NRC, October 27, 1989, " James A. FitzPatrick Nuclear Power Plant Response to Generic Letter 89-16, Installation of a j Hardened Vent." i l
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= h Appendix A :
I
- i MARK I PIANT-SPECIFIC i j
ENHANCED VENTING CAPABILITY REGULATORY ANALYSIS FOR JAMES A. TITZPATRICK NUCLEAR POWER PIANT [
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TABLE OF CONTENTS i
A-1 I
.(1.0STATEMENTOTTHEPR0BLEM...............................
-2.0 OBJECTIVES ............................................. A-2 !
3 . 0 ALTERN ATI VE RES O LUTION S - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2 3.1 Alternative (1) ..................................... A-2 3.2 Alternative (ii) .................................... A-3 3.3. Alternative (iii) ................................... A-4 4.0 CONSEQUENCES .......................................... A-4 4.1 Costs and Benefits of Alternative Resolutions ....... A-4 ;
4.1.1 Alternative (i) .............................. A-4 ;
4.1.2 Alternative (ii) ............................. A-5 A-5 4.1.2.1 Values Risk Reduction Estimates ....... !
4.1.2.2 Impacts: Cost Estimates ............... A-5 4.1.2.3 Value-Impact Ratio .................... A-7 4.1.3 Alternative (iii) ............................ A-7 4.1.3.1 Valuet Risk Reduction Estimates ....... A-7 4.1.3.2 Impacts: Cost Estimates ............... A-7 4.1.3.3 Value-Impact Ratio .................... A-8 4.2 Impacts on Other Requirements........................ A-12 1 4.3 Constraints ......................................... A-12 5.0 DECISION RATIONALI .................................... A-12 5.1 Commission's Safety Goal ............................ A-12 !
I 6.0 IMPLEMENTATION ........................................ A-12 q 16.1 Schedule for Implementation ......................... A-12 1'
7.0 REFERENCES
............................................ A"14 ATTACHMENT 1 TO APPENDIX A - BACKFIT RULE ANALYSIS. . . . . . . . . A-15 ]
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1 Mark I Plant-Specific Fnhanced Venting Capability Regulatory Analysis 1.0 STATEMENT OF THE PROBLEM -
In SECY-89-017 dated January 23, 1989 (Reference 1), the staff presented its findings concerning the Mark I containment Performance ,
Improvement (CPI) program to the commission. One of the improvement that the staff recommended was the installation of hardened vent ,
capability. The Commission concurred with the staff's position and !
directed the staff to proceed with the imposition of a hardened vent
' capability for each boiling water reactor (BWR);with.a Mark I ;
containment where a plant-specific backfit analysis supports such a backfit.
The~ General Electric Company has designed and constructed several BWR
- configurations with three basic containment designs designated as Mark I, Mark II, and Mark III. Probabilistic Risk Assessment (PRA) i Otudies have been performed for a number of BWRs with Mark I i containments. Although these PRA studies do not show the BWR Mark I i
plants to be risk outliers as a class relative to other plant designs, they do suggest that the Mark I containment could be !
challenged by a large scale core melt accident, primarily due to its l cmaller size. However, estimates of the probability of containmen. i failure under such conditions are based on calculations of complex l Occident conditions that contain significant uncertainty. I Draft NUREG-1150 (Reference 2) evaluated the dominant accident coquences for five plants, one of which was a BWR Mark I. The dominant accident sequences were identified as station blackout (SBO),_ which includes the loss of all AC and DC powers and anticipated transient without scram (ATWS). This list would have included the loss of long-term decay heat removal (TW) cxcept that, for the particular plant being reviewed, the likelihood of this coquence was considered to be greatly reduced because of assumed cuccessful venting of the containment. While the TW sequence was not ,
considered in NUREG-1150 to be a dominant sequence for the plant
- reviewed, it can be a significant contributor to overall plant risk for Mark I plants in general. (The June 1989 version of draft NUREG- s 1150 reported similar results for the Peach Bottom Atomic Power Station as were reported in the February 1987 edition.)
All BWRs with Mark I containments have a capability to vent the containment with various size lines. The largest lines usually are ossociated with the vent and purge system used to inert and deinert containment. Venting of containment as an accident mitigative action is permitted in the Emergency operating Procedures (EOPs). In part, the existing vent path uses sheetmetal ductwork from the containment isolation valves through the standby gas treatment system (SGTS) to the plant stack. The sheetmetal ductwork is usually designed for low A-1
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pressure and is expected to fail under severe accident pressures. ;
railure of the ductwork would introduce the containment atmosphere to ;
the reactor building. This could result in harsh environmental conditions that would complicate operator accident recovery actions i within the reactor building and could cause failure of equipment within the reactor building. , i The hard pipe vent would be designed to withstand severe accident 4 pressures, and, thus, would not fail during a TW event thereby olleviating the harsh environmental concerns in the reactor building. l This regulatory analysis studied the costs and benefits of installing o hardened vent capability at BWRs with Mark I containments. I 2.0 Q&JECTIVES The staff objective is to reduce the overall risk in BWR Mark I plants by pursuing a balanced approach using accident prevention and occident mitigation. Most recent PRA studies indicate that TW is an *
. important contributor to BWR Mark I risk. The balanced approach includes (1) accident prevention - those features or measures that '
chould reduce the likelihood of an accident occurring or measures that the operating staff can use to control the course of an accident Cnd return the plant to a controlled, safe state, and (2) accident I Ditigation - those features or measures that can reduce the magnitude of radioactive releases to the environment during an accident.
Although.the staff considered the quantification aspects of both occident prevention and mitigation, this regulatory analysis only quantified the preventive aspects. The proposed hardened vent .
capability would provide enhanced plant capabilities and procedures l concerning both accident prevention and mitigation. l 3.0 ALTERNATIVE RESOLUTIONS Plant' modifications to the containment venting capability are being proposed to reduce the probability of or to mitigate the conse-quences of a severe core melt accident. The proposed modification consists of installation of a hard pipe from the existing Netwell ventilation penetration, bypassing the ductwork to the standby gas treatment system, and going to the plant stack. The ventilation 1 penetration is the 18- to 24-inch penetration normally used as part i of the vent and purge system for deinerting the containment.
For the proposed modifications, the new components need not be cafety-grade or safety-related. However, no failure of the modified cystem or non-safety-related component is to adversely affect any cafety-related structure, system, or component raquired for coping with design-basis accidents.
3.1 Alternative (i)
This alternative is the no-action option, that is, to leave the existing venting capability unaltered.
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The existing venting capability vents the containment through the Cxisting ductwork from the suppression cool to the SGTS. The ductwork design pressure is usually a few psid or less (Reference 3).
Consequently, venting under severe accident conditions could cause failure of the ductwork and a direct release into the reactor building. The discharge of high-temperature gases over an extended '
period of time may pose a threat to the availability or performance of safety-related equipment. The discharge of hydrogen could result in hydrogen burns (or detonations) inside the reactor building.
Electrical cables, motor operators on valves, relays, and contro) room components may fail under these environmental conditions.
Adverse environmental conditions would complicate entry into the reactor building. Calculations from a venting study during an anticipated transient without scram (ATWS) indicate a severe environment would be present in the reactor building during venting cperations (Reference 4). If systems that are needed to terminate the accident need repair, this environment (high temperature and radiation) could hamper recovery efforts by preventing personnel from cntering into the reactor building.
i 3.2 Alternative (ii) i This alternative would involve the installation of a hardened venting capability from the containment wetwell to the plant stack. l The proposed venting improvement would provide a wetwell path to the plant stack capable of withstanding the anticipated environmental conditions of a severe accident. This proposed modification would include the installation of hard pipe from the outlet of an existing wetwell vent outboard containment isolation valve to the base of the plant stack. This pipe would be routed through a new isolation valve that would bypass the existing ductwork and the SGTS. The hard pipe to the stack could contain a rupture disk to prevent inadvertent cperation and release, of radioactivity. The emergency procedures would need to be modified to provide appropriate instructions for the operator. This alternative would mitigate the consequences of severe Cecidents by reducing the likelihood of core melt from the TW coquence. All releases through the vent would pass through the cuppression pool, and the particulates would be scrubbed.
During a loss of long-term decay heat removal accident, this alter-native would prevent failure of tne vent path inside the reactor building and would result in an elevated release. The elevated release could reduce the offsite consequences. Since the vent path chould not fail insido of the reactor building, personnel could repair equipment and perform other plant recovery activities in the reactor building. Furthermora, there would be no harsh environmental conditions to degrade or fail other equipment. There is the possibility of inadvertent operation of the vent that would release come radioactive material without any holdup time or filtration.
This alternative would not affect the releases of radioactive A-3
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l taterial for those sequences where the dryvell fails, such as from corium attack, once the drywell shell has failed.
l 3.3 Alternative (iii) i l This alternative would involve alternative (ii) plus the instal-lation of an external filter system. .
l The proposed venting improvement includes the hard pipe vent discussed in alternative (ii) plus the installation of an external ,
filter system, such as the Filtra system or the Multi Venturi l Scrubbing System (MVSS). This external filter would be installed cutside of the existing facilities. A single external filter unit could be constructed to service multiple containments with proper isolation valves. Both the Tiltra and the MVSS systems do not rely en AC power to perform their intended functions. Similar to 01ternative (ii), the emergency procedures would need to be modified i to provide appropriate instructions for the operator. This ,
citernative would mitigate the consequences of a severe accident and could reduce the likelihood of core melt if the operator transfers cuction of the injection pumps from the suppression pool to an ,
alternate source of water, such as the condensate storage tank, before venting containment. With the external filter, the amount of particulate removal of the external filter would not be sensitive to the conditions in the suppression pool. No significant additional risk reduction was estimated to result from an external filter system in addition to the suppression pool scrubbing. Since all particulate releases through the hardened vent (alternative 11) are scrubbed, the cxternal filter will only provide minimal additional scrubbing. The external filter provides no additional benefit in core melt prevention although it would provide filtration and some holdup time for inadvertent operation of the vent. Similar to alternative (ii), l this alternative would not affect the releases of radioactive l caterial for those sequences where the drywell fails, such as from j corium attack, once the drywell shell has f ailed. >
4.0 CONSEQUENCES 4.1 ggsts and Benefits of Alternative Resolutiong The staff used available PRAs to estimate the incremental benefit of the three alternatives discussed in the following paragraphs. The cnly accident sequence that is being considered for this analysis is the TW. This is considered to be conservative since the alternatives could have a beneficial but small effect on other sequences (Reference 5). The staff estimated the change in the CDF, but not the total CDF from internal events (Reference 6).
4.1.1 Alternative (i)
This alternative would be to take no action. Since it is expected that the ductwork would fail if the containment were vented at high A-?
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a pressure, this approach would not only jeopardite personnel, but also !
, the ability to regain control of the facility during the accident, i' l Furthermore, based on a generic regulatory analysis (Reference 1) the l
C:mmission instructed the staff to require hardened vent capability !
! fcr plants for which it could be shown to be cost effective. i' Therefore, baned on the discussion below the no-action alternative is n;t recommended.
l 4.1.2 Alternative (11) 4.1.2.1 Valuet Risk Reduction Estimates For those accident scenarios where containment failure results in '
core degradation and a severe accident, the approach using a hard pipe vent path could reduce or delay core degradation. This is estimated to reduce the total core damage frequency per reactor year by 4.5E-5. Corresponding to a release of 1.46E6 man-rom, this represents a risk reduction in man-rem per reactor year of 65.5.
4.1.2.2 Impacts: Cost Estimates The estimated cost for installation of the hard pipe vent path is 0.68 million dollars (Reference 7).
The averted cost associated with prevention and mitigation of an accident can be discussed as f4ve separate costs: replacement power, cleanup, onsite occupational health impacts, offsite health impacts, and onsite property damage. To estimate the costs of ,
averting plant damage and cleanup, the reduction in accident frequency was multiplied by the discounted costs of onsite property. The following equations from NUREG/CR-3568 (Reference 8) ,
were used to make this calculation:
V ,= NdFU ;
U= (C/m) ( (e""U) /r#) (1-e"""h"'H) ( 1-e"*)
where (cited values are from Table 2)
V, = value of avoided onsite property damage ($)
l N = number of affected facilities = 1 dr = reduction in accident frequency = 4.5E-5 /RY U = present value of onsite property damage ($)
C = cleanup and repair costs = S1.0 bilijon i t(f) = years remaining until end of plant ljfe = 25 t(i) = years before reactor begins operation = 0 r = discount rate = 10%
a = period of time over which damage costs are paid out (recovery period in years) = 10 l
Using these values, the present value of avoided onsite property damage is estimated to be $261,105.
A-5
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Replacement power costr> can be estimated using NUREG/CR-4012 (Raference 9), which lists the replacement power costs for each
- nuclear power reactor by season. Using this information for only-
.? Mark I reactors averaged over the four years of projected data and escalated by six percent for 1989 dollars, the g neric replacement .
. power cost is $400,666 per day. (The plant-specific replacement power cost-is shown in Table 3. NUREG-1109 (Reference 10) used a generic coct of $500,000 per day and compares favorably with NUREG/CR-4012.)
The change in public health risk associated with the installation of the proposed hardened vent system is expressed as total man-rem of avoided exposure. The following equations from NUREG/CR-3568 j
1 were used to make this calculation:
=
V,, = NT (D, x R)
< where:
V,, = value of public health risk avoided for net-benefit method ($)
H = number of affected reactors = 1 T -= average remaining lifetime of affected facilities (years) = 25 D, = avoided public dose per reactor-year (man-rem /RY)
= 65.5 R = monetary equivalent of unit dose ($/ man-rem)
=-$1000 Using these values, the evoided public health exposure of 1.638 million dollars is obtained for FitzPatrick. Considering a possible 20-year operating life extension, the value or avoided public health exposure is 2.948 million dollars.
The occupational health risk avoided because of the installation of the proposed hardened vent system is expressed as man-rem of avoided exposure. The following equations from NUREG/CR-3568 waro used to make this calculation:
Vag = NT (D, x R) where:
V,a = value of occupational health risk due to accidents avoided ($)
N = number of affected reactors (reactors) =1 T = - average remaining lifetime of affected facilities'(years)=25 Du = avoided occupational dose per reactor year (Man-Rem / Reactor-Year)
R = monetary value of unit dose ($/ Man-Rem)=$1000/ Man-rem A-6 l
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Thero are two types of occupational expcaure elat tid to accidents, immediate and long-term. The first ocer 9 at the time of the accident and during the immediate mankgament en,' the emergency. The second is a long-term exposure, presumably a* significantly lower individual rates, associated with the cleanup and refurbishment of the damaged facility. The best estimate of the immediat's .
occupational exposure as specified in NUREG/CR-3568 is 1000 man-rem. The best estimate of the long-term occupational exposure as specified in NUREG/CR-3568 is 20,000 man-rem. This results in
, occupational exposure of 21,000 man-rem. The multiplication of' 21,000 man-rem by the reduction in CDF, 4.5E-5 per reactor year, produces the avoided occupational dose per reactor year, D .
Using these values, the prese nt value of avoided occupational
. health exposure was calculated to be $23,625, approximately one to two percent of the public healtn risk, and is not considered to be a significant contributor. Therefore, the occupational health.
exposures will not be considered further.
4.1.2.3 Value-Impact Ratio The value-impact ratio, not including the costs of onsite accident avoidance, is 2408 man-rem averted per million dollars. If the savings to industry from accident avoidance (cleanup and repair of onsite damages and replacement power) were included, the overall value-impact ratio would be -15366 man-rem averted per million dollars. Considering a likely 20-year operating life extension, the overall value-impact ratio would be -17609 man-rem averted per million dollars.
- 4.1.3 Alternative (iii) 4.1.3.1 Value: Risk Reduction Estimates This alternative would provide minor additional particulate scrubbing for the hard vent. However, because all particulate releases will have been scrubbed by the suppression pool, the improvement over alternative (ii) could be minimal.
4.1.3.2 Impacts: Cost Estimates External filters were estimated to cost $10 million to $50 million for the Filtra design anu about $5 million for the Multi-Venturi Scrubber System design.
'Using the same equations given in alternative-(ii), the present value of the estimated avoided onsite damage to property is
$261,105. Similarly, the estimated replacement power cost is $201 million per year. Thus, the estimated avoided damage to onsite property and the replacement power is $786,578.
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The present value of the change in the estimated public health risk associated with the installation of the hard vent and the external filter is $1.638 million.
4.1.3.3- Value-Impact Ratio
-The overall value-impact ratio of this alternative is in terns of man-rem ~ averted per million dollars. If the savings to industry from accident avoidance (cleanup and repair of onsite damages and replacement power) were included, the overall value-impact ratio would be 335 man-rem averted per million dollars. This is calculated from the value in Column G of Table 2 divided by-the installation cost in Column H of Table 2 and added 5 million dollars for the MVSS design minus the value in Column H of Table 2.
This-alternative is not recommended because it does not provide substantial additional safety benefit over alternative-(11) and is not cost effective. .
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i Table IL--Cost Benefits of Alternatives (i)-(iii) i (man-rem averted per million dollars) l l
Alternative.(i) - do nothing, O l Alternative (ii)' - hard pipe venting l for the remaining life -15366 with.20-year life extension -17609 Alternative (iii) - hard pipe venting 335
+ MVSS-external filter i
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t -- 0.00 - 2988 t?60,te5 St 617.597 123,63 81st.2es 590 5786,575 ' 4151e6 :
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TCble 3 - Estimated-Replacement Power Costs
, (in dollars per day) ;
1 Est., Cost i
- Yeait Est. Cost- Est. Cost Reactor Name MWe Licensed 1985$ 1989$ (per . year) [
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'FitzPatrick~ 816' 1975 $444,650 $551,366' $201,248,590
-1 Notes: 1:NUREG/CR-4012 (Table S.1) provides' replacement power costs '
for all' plants on per plant / season basis--for 1987-1991.
2:The inflation rate used is 6 percent / year,. and.the discount 3 l
T rate:used is 10 percent / year. ,
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4.2 -Imoacts~on other Renuirements
- Theret are six programs related to severe accidentst Individual. Plant Examination (IPE) ,. Containment- Performance Improvement (the topic of i,. this. regulatory analysis), Improved Plant Operations, Severe Accident Research Program,. External Events, and Accident Management. Each of the five programs related to Containment Performance Improvement
' (CPI) will be discussedibriefly in Item 3 of Attachment 1, Backfit-e,
, Rule Analysis.,
4.3- ' constraints.
The plant-specific imposition of a hardened vent is constrained by.
the' guidelines of U.S. NRC Manual Chapter 0514, "NRC Program for
, Management,of Plant-Specific Backfitting of Nuclear Power Plants",
- which is based on the backfit rule (10 CFR 50.109), as published by.
4 the Commission on September 20, 1985, and-the provisions of 10 CFR 50 Appendix 0, 10. CFR 50.54 (f) ,- and 10 CFR -2. 204.
No other constraints ~have been identified that affect this program.
5 '. 0 1 DECISION RATIONALE
.The' evaluation lof.the CPI program included deterministic and probabilistic analyses. . calculations to estimate-the CDF and the-consequences 1 of=the TW sequence were. performed using information available;from'the NUREG-1150-program and from existing PRAs.
The best estimate of the contribution of TW to the total plant CDF' expressed'in events per reactor year for.FitzPatrick is 4.5E-5.
. Implementation of.the proposed hardened venting capability will cause
- TW;to be-a minor' contributor to the' total-CDF and'will significantly 3 reduce the total risk'to the health and safety to the publ i c.
5.1 commission's Safety Goal OneAugustL4, 1986,:the' Commission published in the Federal Reaister a ipolicyLatatement on " Safety Goals for the Operations of Nuclear Power (Plants" (51 FR 28044). 'This policy statement focuses on the risks to-ltheJpublic~ from nuclear power: plant- operation and establishes goals.
that broadly define an: acceptable level.of-radiological. risk. The'
' discussion:in the'Re 11atory Analysis of SECY E9-017 addressed the CPI' program'recomm- ation in light of these coals.
Y' 6 s 0 '- IMPLEMENTATION t6.1 schedule for Imolementation m
TheLlicensee may reconsider its position on the installation of the hardened:ventLunder the provisions of'10 CFR 50.59. Without the
~
licensee's1 commitment, the staff intends to pursue an order after 30 days'of.its receipt of this analysis, requiring this backfit under A-12 6
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. - . . - . .. - - .. ~ . . - . - . - . . . .
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. the provision of 10 CFR 50.109. Within 60 days after issuance of the
- backfit order, the, licensee.will be required to submit to-the NRC-a cchedule-for implementing any necessary equipment-and procedural aodifications to meet the performance goals and to provide adequate d3fense-in-depth. All plant: modifications are.to be installed, procedures: (including the decision making process-for venting).
rcvised, and. operators trained not later than January _1993. '
otl.or' schedules were' considered; however, the staff believes the i
. proposed implementation of the hard pipe vent capability can be 1 - largely performed-with minimum interfacing with containment and ongineered safety feature systems and thus with'the plant online.
Therefore,1the licensee can install the proposed modification without unnecessary financial burden for plant shutdown. The schedule allows reasonable time for.the-implementation of necessary hardware-to cchieve a reduction in the risk from TW. Shorterfor less flexible e cchedules would be unnecessarily' burdensome. I i
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4 f7. 0, REFERENCES o 1. SECY-89-017, " Mark I Containment Performance Improvement Program," January 23, 1989. '
- 2. NUREG-1150, (Draft), " Reactor Risk Reference Document,"
-February 1987.=
3.. NUREG/CR-5225, "An overview of Boiling Water Reactor Mark I
' Containment Venting Risk Implications," October'1988.
- 4. . Harring, R.M., " Containment Venting.as a Mitigation Technique-
.for BWR' Mark I Plant'ATWS," 1986 Reactor Water Safety Meetina.
Gaithersbura. Maryland, October 1986.
5.1 NUREG/CR-5225, Addendum 1, "An overview of Boiling Water Reactor Mark I containment Venting Risk Implications, An ,
't Evaluation of Potential Mark I Containment Improvements," June 1989. ,
- 6. Sharon, B.W., Memorandum to.Thadani, A.C., " Reduction in Risk ~
from the Addition of Hardened. Vents in BWR Mark I. Reactors,"
October 19, 1989.
- 7. Letter From-John C. Brons (New York Power Authority) to U.S.
NRC, October 27, 1989, " James A. FittPatrick Nuclear Power Plant Response to Generic Letter 89-16, Installation of a
. Hardened ~ Vent."
- 8. -NUREG/CR-3568, "A Handbook for Value-Impact Assessment,"-
' December 1983.
9.> NUREG/CR-4012, " Replacement Energy Costs for Nuclear Electricity-Generating Units in the United States:'1987-1991'," January 1987'.
- 10. NUREG-1109, " Regulatory /Backfit Analysis,for the Resolutian'of Unresolved Safety Issue A-44, Station Blackout," June 1988, w
., 11'.- SECY-88-147, " Integration Plan for closure of Severe Accident Issues," May 25, 1988.
- 12. Memorandum from S. J. Chilk to V. Stello, "SECY-89-017 - Mark I Containment Performance Improvement Program," July 11, 1989.
A-14
. ATTACHMENT 1 TO APPENDIX A BACKFIT RULI ANALYSIS Analysis and Determination That the Recommended Hard pipe Vent Capability for Containment Performance Improvement Compl.ies with the Backfit Rule 10 CFR 50.109 The Commission's 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, As SS, 56, and evidenced
- 57) with respect to design basisaccidents accidentcouldconditions.
progress beyond design by the accident at TMI Unit 2, basis considerations and result in a severe accident. Such an Existing accident could challenge the integrity of containment.
regulations do not explicitly require that nuclear power plant containments be designed to withstand severe accident conditions.
The staff and our consultants studied this issue as part of the severe accident program for the General Electric Company boiling water reactors (BWRs) with Mark I containments. BWRs with Mark I containments were reviewed first because of the perceived susceptibility of the Mark I containments to failure based, in part, on the small containment volume of the Mark I containment design.
Both deterministic and probabilistic analyses were performed to evaluate the loss of long-term decay heat removal (TW) in challenging containment integrity and potential failure modes affecting the likelihood of core melt, reactor vessel failure, The containment risk analysis failure, shows and risk to the public health and safety.
that the risks from plants with Mark I containments are generally similar to the risks from plants with containments of other types.
In addition, the hardened pipe vent capability is not needed to
.providt e.dequate protection of the public health and safety. Rather, the proposed plant improvement will provide substantial cost-effective enhancement to Mark I plant safety.
The estimated benefit from implementing the proposed hard pipe vent is a reduction in the frequency of core melt caused by TW and the The associated reduction in risk of offsite radioactive. releases.
estimated risk reduction in terms of man-rem is 1638 and supports the conclusion of the Commission that implementation of the proposed improvement provides a substantial improvement in the level of protection of the public health and safety.
The estimated. cost to the licensee to implement the proposed safety enhancement is 0.68 million dollars. This cost would be primarily for the licensee to 1) assess the plant's capability, 2) install equipment to provide additional pressure relieving catability, 3) revise the emergency operating procedures, and 4) provide operator training concerning mitigating the TW sequence.
The estimated value-impact ratio, not including accident avoidance A-15
.i.i___... - . . . . , . _ . .
=-
costs, in terms of man-rems averted per million dollars is 2408. If the net cost, which includes the cost savinge from accident avoidance (i.e. cleanup and repair of onsite damages and replacement power following an accident), was included, the estimated overall value-impact in terms of man-rems averted per million dollars would be -
15366. If 20 years of life extension were included, the estimated overall value-impact in terms of man-rems averted per million dollars would be -17609. These values support proceeding with the proposed hard pipe vent capability improvement.
Although tht preceding quantitative value-impact analysis was one of the factors considered in evaluating the proposed improvements, other factors were considered as a part in the decision-making process.
PRA studies performed for this issue have shown that the loss of long-term decay heat removal (TW) events can be a significant contributor to core melt frequency. With consideration of the conditional containment failure probability, TW events can provide an important contribution to reactor risk.
Although there are licensing requirements and guidance for providing a containment and support systems to contain any release of material from the reactor vessel, containment integrity may be significantly challenged under severe accident conditions. In general, active systems required for reactor and containment heat removal are unavailable during the TW event. Therefore, the offsite risk is higher from a TW event than it is from many other types of accidents.
The containment integrity is primarily challenged by over-pressure for the TW events. Under certain conditions, failure of the containment can also initiate core degradation.
The estimated frequency of core melt from TW events is directly proportional to the frequency of the initiating events. The estimate of the TW frequency for FitzPatrick was partly based on information provided in draft NUREG-1150, " Severe Accident Risks: An Assessment for Five US Nuclear Power Plants," for the Peach Bottom Atomic Power Station, Unit 2, and other available PRAs. This is assumed to be a realistic estimate of the core melt frequency when compliance with 10 CFR 50.63, the Station Blackout Rule, has been achieved.
The factors discussed in the previous paragraphs support the determination that the additional defense-in-depth provided by the ability to cope with a TW event would substantially increase the overall protection of the public health and safety. Also, this increased protection will justify the direct and indirect costs of implementation.
Analysis of 10 CFR 50.109(c) Factors (1) Statement of the soecific obiectives that the backfit is desianed to achieve The objective of the proposed hard-pipe vent capability is to A-16
5 g_
g reduce-the risk from TP-events by reducing the likelihood of core melt and to--mitigate releases given a TW or other similar events leading to core melt.
(2) General descrietion of the activity rearired by the licensee or-anolicant in order to comolete the backfit -
To comply with the proposed improvement in nontainment venting, the licensee will be required to:
- - Evaluate the actual capability of the existing containment vent system'to withstand the anticipated-containment temperatures and pressures without failing any portion of-the vent path to the plant stack Evaluate the actual capability of the existing containment s
' vent: isolation valves to be opened and closed under anticipated containment pre.ssures and vent flow rates during severe accidents involvino TW sequences.
- Determine the'necessary plant modifications to ensure a hard-
' pipe vent path will be available under TW events, develop a schedule.for plant modification, and submit the schedule to the NRC within 60 days from the issuance of the backfit order.
- Complete-the nececsary modifications by January, 1993.
The-licensee will be required to have the decision making process, the procedures and training to cope with and recover from a TW-severe accident. These' procedures should conform to the_ Emergency Procedure Guidelines of the Boiling Water' Reactor owner's Group.
' The'notential safety imoact of chances in clant or onerational (3)~
comolexity, includina the relationshin to Dronosed'and o=
existina reaulatory recuirements
.The hardened vent capability to cope with the.TW event should not add to plant or operational: complexity, because the vent is-normally closed and not operated during normal power operation.
Although this system does add some additional hardware to-the
, plant, it is a simple system. The containment performance
-improvement:(CPI) program is related to implementation of the Commission's Severe Accident Policy Statement as defined in SECY-88-147-(Reference 11). In SECY-88-147 the staff' described the.
Various programs underway related to closure of severe accident-issues. Included among these was'the CPI program. Other programs described in SECY-88-147 are related to the CPI program as the
-following' discussion indicates.
- Individual Plant Examination (IPE)
The IPE involves the formulation of an integrated and A-17 u.
I I
systematic approach to an examination of each nuclear power plant in operation or under construction for possible significant plant-specific risk contributors that might be missed without a systematic search. Supplement 1 to Generic
- - Letter 88-20 requested that Merk I licensees include in their IPEs the proposed plant improvements identified in SECY 017, other than the hardened vent, namely operation of the enhanced automatic depressurization system, and alternative low-pressure water supply for injection into the reactor vessel and for containment sprays. The examination will carefully examine containment performance in striking a balance between accident prevention and consequence mitigation. The IPE program may require three to four years until the last plant has performed the IPE.
- Improved Plant Operations (IPO)
The IPO includes consideration of continued improvements in the following areas: 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 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, and the effectiveness of operational reliability methods to help identify potential problems early and prevent their occurrence. The IPO is related to the CPI program's recommendation since we recommend improved procedures and operator training to use the proposed hard vent system.
- Severe Accident Research Prog wm (SARP)
The SARP was begun after the Three Mile Island, Unit 2, (TMI-
- 2) accident in March 1979 to provide the Commission and the NRC staff with the technical data and analytical methodology needed to address severe accident issues. This program has provided input to the NUREG-1150 program and to the CPI program. Additional research is being carried out to evaluate the need for and feasibility of core debris controls.
Research will also confirm and quantify the benefits of having water in the containment to either scrub fission products or to prevent or delay shell melt by core debris.
- Accident Management A-18
u.
The_ accident management program addresses certain preparatory Ut _and recovery measures that: plant operating and technical' staff can perform to prevent or significantly mitigate the-consequences;of a severe accident. This program includes the following~ measures to be performed by the plant staff: 1) prevent core damage, 2) terminate the progress of core damage if it begins'and retain the core within the reactor vessel, 3) failing_that, maintain containment integrity as long as possible, and 4) minits te the consequences of offsite releases. _The plant enhancement recommended by the CPI program would provide the accident management' program with additional capability to achieve their goals by providing
' improved hardware with which to deal with a severe accident..
"The procedures for using-the vent should be re-examined'under the Accident = Management program.
(4) Whether the backfit is interim or final and, if interim, the justification for imposina the backfit on an interin basis The proposed hardened-vent capability is not an interin measure.
'(5) . Potential chance in the risk to the oublic from the accidental offsite release of radioactive material Implementation of the proposed hardened-vent capability is expected
-to resultnin an estimated risk reduction to the public of'1638 man-rem over the. remaining plant life.
'(6) Potential innact on radioloaical tfmosure of facility emolovees Although the reduction.in occupational exposure caused by reduced CDF-and associated post-accident cleanup and repair _ activities-has-
- notfbeen quantified, it could be substantial if-the hardened vent prevents contamination of the reactor building. The estimated total; occupational exposure for installation of the hardened-vent
. path should1be negligible. No increase in' occupational exposure is expected from operation and maintenance of the hardened-vent system.- In-fact, if the vent is'ever used, it should decrease the risk to employees because of'the reduced potential for vent path ;
failure and the'resulting reactor building contamination.
(7)
Installation and continuina costs associated with the backfit, includina the cost of facility downtime or the cost of construction delav Because the plant can be operating during most of the installation, there are no significant costs associated with construction delays.
With the exception of connections to the existing piping the hardened-vent path can be installed with the plant operating and the' work completed during normal plant outages without an adverse A-19
7
=
impact on the outage schedule. Thus, there are no costs associated with additional plant downtime.
The estimated cost of the hardened vent system is 0.68 million dollars.
(8) The estimated burden on the NRC associated with the b'ackfit
-and the availability of such resources With an estimated expenditure of 200 man-hours for review of the
-submittals, the estimated total cost for NRC review of industry submittals is $17,000. The staff will concentrate on the review of design criteria and the method to incorporate the venting into emergency operating procedures.
(9) Consideration of imoortant aualitative factors bearina on the need for the backfit at the carticular facility The installation of the hardened vent will provide greater flexibility in managing accidents other than the TW events, and ,
will provide defense in depth.
(10) Statement affirmina accrooriate interoffice coordination related to the crocosed backfit and the clan for imolementation The licensee may reconsider its position on the installation of the hardened vent under the provisions of 10 CFR 50.59.
Without the licensee's commitment, the staff intends to pursue an order after 30 days, requiring this'backfit under the provision of 10 CFR 50.109. The proposed backfit was developed as a cooperative effort between the offices of Nuclear Regulatory Research (RES).and Nuclear Reactor Regulation- (NRR) with consultation with the Office of General Counsel. The implementation is being handled within the NRR.
The staff considered implementation schedules consistent with the guidelines provided by the commission (Reference 12).
Within 60 days after issuance of the backfit order, the licensee is to provide to the NRC a schedule for implementing any equipment and procedural modifications necessary to meet the performance goals and to provide adequate defense-in-depth. All plant modifications are to be installed, procedures revised, and operators trained not later than January 1993.
(11) Basis for reauirina or nermiteina isolementation on a carticular schedule Although other schedules were considered, the staff believes the proposed implementation of the hard pipe vent capability can be performed with minimum interfacing with containment and engineered safety feature systems and either with the plant online or during a A-20 Il I
a._... .. ,,, . . . ,. ,
normal refueling outage. Therefore, the staff believes the schedule is achievable without incurring unnecessary financial burden on the licensee for plant shutdown. The schedule allows reasonable time for the implementation of necessary hardware to reduce the risk from TW and allows appropriate coordination with IPE program. Shorter or less flexible schedules would be unnecessarily burdensome.
(12) Schedule for staff actions involved in isolementation and verification of inclementation of the backfit, as aoorooriate The proposed backfit is to be installed under 10 CFR 50.59Therefore, for most of plants and, thus, will require minimal staff effort.
timely staff review will be expected. However, for those plants that choose not to implement the modifications under 10 CFR 50.59, more staff time and efforts will be involved.
(13) Imoortance of the crocosed backfit considered in licht of other safetv-related activities underway at the affected facility The proposed backfit should not directly involve any other safety-related activities that may be underway at the affected facility.
(14) Statement of the consideration of the orocosed clant-soecific backfit as a notential ceneric backfit Initially, the staff proposed the installation of hardened vent as a generic backfit. The Commission directed the etaff to implement it as a plant-specific backfit considering the plant differences in risk reduction and benefits to be gained from a generic cackfit.
A-21 :
4
+. ,_e c s= ,
h 'e
- ,3 improvement (CPI)? program is related to implementation.of the Commission's Severe Accident Policy Statement as defined in SECY-c 88-147F(Reference 11). In SECY-88-147 the staff described the various= programs. underway related to-closure of severe accident issues. Included among these was the CPI program. .0ther-programs described ~in SECY-88-147 are related to the CPI program as the-following discussion indicates.
- Individual Plant Examination-(IPE)
The IPE' involves the formulation of an integr;ted and systematic approach to an examination of each nuclear power plant in operation _or under construction for-possible significant plant-specific risk contributors that might be missed >without a systematic search. Supplement'l to Generic Letter 88-20 requested that Mark I licensees = include in their IPEs the proposed plant improvements identified in SECY-89-017, other than the hardened vent, namely operation ,
of the enhanced' automatic depressurization system, and alternative low-pressure water supply for injection into the reactor vessel and for containment sprays. The examination will carefully examine containment performance in striking a balance between accident prevention'and consequence mitigation. The IPE program any require three to four-years until the last_ plant has performed the IPE.
- ' Improved Plant operations (IPO)
The- IPO includes consideration. of continued improvements in the following areas: Systematic Assessment.of Licensee Performance (SALP) program; regular reviews by senior NRC staff managers to identify and evaluate-those plants that mayenot be meeting NRC and industry standards of operating-performance; diagnostic team inspections;' improved plant.
' Technical Specifications; improved operating procedures; expansion 1of the 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, and the effectiveness'of operational reliability methods to help
. identify potential problems early and prevent their occurrence. The IPO is related to the CPI program's e
recommendation since we recommend improved procedures and operator training to use the proposed hard vent system.
-* Severe Accident Research Program (SARP)
A-18 i
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The SARP was begun after the Three Mile Island, Unit 2, (TMI-2)< accident in March'1979 to provide the Commission and
' thefNRC: staff with the technical data and analytical m , . methodology needed to address. severe accident issues. This program has provided input to the NUREG-1150 program and tcr the CPI. program.. Additional research is being carried out toievaluate the~need for and feasibility of_ core debris controls. Research will also confirm-and' quantify the
' benefits-of-having water in the containment to either scrub fission products or to prevent or delay'shell melt by core:
debris.
- ' Accident Management The accident management-program addresses certain preparatory and recovery measures that plant operating and technical staff can perform to prevent or significantly mitigate the consequences of a severe accident.= This-program includes the following measures to be performed by the. plant staff: 1) prevent core damage, 2)-terminate-the progress of core damage if itLbegins-and retain:the-core-within tho' reactor vessel, 3) failing that, maintain .
m containment < integrity as long as possible, and:4) minimise; the: consequences of offsite releases.= The plant enhancement-recommended by the CPI program would provide the accident
-management program with additional capability to achieve their, goals by providing improved hardware with which to deal with a. severe. accident. The-procedures for using the vent should be re-examined under the Accident Management program.
.(4) Whether'the-backfit is interin or final-and. if interim,-the justification for imoosina the backfit on an interim basis-The proposed hardened-vent capability is not an. interim measure.
( 5 ) -- Potential chance in the risk to the oublic from~the accidental-offsite release of radioactive material I'aplementation of the proposed hardened-vent capability is expected--to' result in-an estimated risk reduction to the'public of 738 man-rem over-the remaining plant life. .
(6). Potential imoact on radioloaical exoosure of facility emolovaes Although the reduction in occupational exposure caused by reduced CDF and associated post-accident cleanup and repair activities-A-19 1 f i
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L has not been quantified, it could be substantial if the hardened vent prevents contamination of the reactor building.. The estimated total occupational exposure for installation of the.
hardened-vent path should be negligible. No= increase in A
- occupational exposure is expected from operation and maintenance of the hardened-vent system. In fact, if the vent *is.ever used, it should decrease the risk to employees because of the reduced potential for vent path failure and the resulting reactor building contamination.
(7) Installation and continuina costs associated with the'backfit, includina the cost of facility downtime or the cost of construction delav Because the plant can be operating during installation,.there are M no costs associated with construction delays. The hardened-vent path can be installed with the plant operating or during_ normal plant outages. Thus, there are no= costs associated with additional plant downtime.
The estimated cost of the hardened vent system is 1.1 million dollars.
'(8) The estimated burden on the NRC associated with the backfit and the availability of such resources With an estimated expenditure of 200 man-hours for review of the submittals, the estimated total cost for NRC review of industry-submittals is $17,000. The staff will concentrate on the review
-of design criteria and the method to incorporate the venting into emergency operating procedures.
(9)~ need consideration of imoortant aualitative factors bearina on'the for the backfit at the carticular facility The installation of the hardened vent will provide greater flexibility in managing accidents other than the'TW events,-and will~ provide: defense in depth.
(10)? Statement affirmina anorocriata= interoffice coordination related to the crocosed backfit and the clan for isolamentation The licensee may reconsider its position on the installation of the hardened vant under the provisions of 10 CFR 50.59. Without the licensee's commitment, the staff intends'tu pursue an order after:30 days, requiring this backfit under the provision of 10
' s~
CFR 50.109. The proposed backfit was developed as a cooperative r'
ef fort between the offices of Nuclear Regulatory Research (RES) and Nuclear: Reactor Regulation (NRR) with consultation with the s
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office of General Counsel. The implementation is being handled within the NRR. The:st?ff considered implementation schedules ,
consistent with the guidelines provided by the Commission !
J (Reference.12). Within 60 days after issuance of the backfit.
order, the licensee is to provide to the NRC a schedule for h
implementing any equipment and procedural modifications necessary ~
to meet-the performance goals and to provide adequate defense-in-depth.. All plant modifications are to be installed, procedures revised, and-operators trained-not later than January l 1993.
(11) Basis for reauirina'or earmittina imolementation on a carticular schedule Although other schedules were considered, the staff believes the proposed implementation of the hard pipe vent capability can be 1 performed with minimum interfacing with containment and engineered safety feature systems and either with the plant online or during a normal refueling outage. Therefore, the staff believes the schedule is achievable without incurring unnecessary financial burden on the licensee for plant shutdown. The schedule allows reasonable time for the implementation of necessary hardware to reduce the risk from TW.and allows appropriate coordination with IPE program. . Shorter or less flexible schedules would be unnecessarily burdensome.
(12); Schedule for staff actions involved in innlementatior_And j verification of imolementation of the backfit, as- acrerocriate I The proposed backfit is-to be installed under 10 CFR 50.59=for most of plants and,'thus,-will require minimal staff offort. l Therefore, timely staff review will be expected. However, for i those plants that choose not to-implement the modifications under j 10 CFR:50.59, more staff time and efforts will be involved.
-(13).Imoortance of the crocosed backfit considered in licht of other safetv-related activities underway at the affected facility The proposed backfit should not directly involve any other safety-related activities that may be underway at the affected-facility.
~(14)7 Etatement of the consideration of the crocosed clant-soecific backfit as a notential cenerie-backfit Initially,-the staff proposed the installation of hardened vent 4 as n' generic backfit. .The Commission directed the staff to !
implement it as a plant-specific backfit considering the plant-differences in risk reduction'and benefits to be gained from a A-21 a
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.j RESPONSE TO )
COMMENTS Id NYPA t,ETTER (JPN 89-70) DATED DCTOBER 27*, 1939 ,
General ter*ents: ;
l
- 1. The letter Questions the "scecial treatsent" of the harcened vent anc-trdicates it should be put in the !FE orocess like the other recommended Mark 1-isprovements.
l Response The hardened vent is not being treated specially, but is being pursued in a sanner stellar to any other "backfit" and consistent _-
with NFC rules and' procedures. The.!PE process 15 riot a vehicle to take regulatory requirements, and it would be improper to use it as such. The decision to pursue the requirement for a 1
~ hardened . vent was apprcved by the Consission, if supported by a e
technical basis ar.d estabitshed procedures and rules are !
followed. :
l
- 2. The letter notes that the cost-benefit analyses in SECY-99-017 are I generic and-not acclicable to Fit: Patrick. The low population of the~ j site is highlighted as a-sajor factor in invalidating-the analyses. l
'1
, Response The analyses followed standard practice.in attempting to evaluate j known plant-specific differences.- Further, the site population j and tne cost estimate provided by NYPA are used in the current i analysis. 'l Soecific Coesents:-
- 3. On page 4, the next-to-last paragraph contains.the statement: "These
!cw' risks were achieved [in the' Peach Bottos NURE6-1150 analyses) ... ,
-without dependence on a hardened' vent."
- 'I Response This statement is in error. The NURE6-!!50 analyses assumed that .
venting through an existing hardened vent was successful. The !
technical analyses supporting SECY-09-017 used the~ Peach Bottos !
results, but'had to rebasetine the results by removing the i assumption of successful' venting through a hardened path to W provide a baseline for benefit analyses.
I 4.. : On page 4, the last paragraph contains the statement that NURE6-1150
' identified drywell shell failure as the major containment failure mode for Mark I plants, yet the hardened vent is ineffective in preventing B-1
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i
4
,o n p-
, _ o,e-i this-failure pode.- "Consecuently, the hardened' vent ... is
- inconsistent with the original purpose of the ... Progree.'-
, P.esponses The CP! orogras looked at all sedes of containment failure, as well as the prevention of severe accidents.. The hardened vent is attractive because tt both crevents and citigates some core Seit accidents. Although resolution of the liner uselt.assue will>not occur for lose time, the tsportance of this-issue 15 great!v reduced 14 the'probattltty of core selt is reduced.
- 5. The basis for the cost-benefit equations are questioned on page-6 and
.7.
Response We believe this equation as correct, but solutions aust be .
correctly interpreted. If the denominator is zero,=the solution is indeterminate, but we would know"that this seans that any benefit gained has no associated not cost. This'uould be a-favorable result. The regulatory analysis.does not blindly sake-use of this equation. Individual values of installation cost, averted exposure, averted onsite costs, and sensitivity studies
~"
=are displayed both separately and in various combinations to provide as complete a. picture as possible. In addition, other e# . factors enter the equation besides the cost-benefit ratio. For example, the backfit rule requires that the benefit of a backfit
.aust be significant in addition to the backfit being cost-effective.
.6. -The need to' calculate-the present worth off health effects is proposed..
Responset Although the draf t Electric Power *, search Institute (EPRI) report is not available to us ;nd therefore me can not respond to it, the NRC policy is to riot discount health. effects.
Discounting radiation induced health effects raises ethical and~
soral questions. Furthermore, the concept of present morth was derived for-sconceit entities with long lives and based on the fungibility of money. Neither of-these concepts completely applies to human health effects. Illustrative of the difficulties in-discounting health effects is the assesseent of the dose ef f ects free radioactive weste over long periods.
Discounting would lead to the anomalous conclusion that there is
, g, little or no present value in averting future doses.
, 7. Page 0 indicates that venting can have both-benefits and detrisents and:that'the net.rtsk should be used. In addition, exposure to persons installing the vent should be used.
Response We agree that venting has both' negative and positive risk 7
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1 aspects. The bac6iit is designee to_recute the risk potential free an esisting erecedure-cy ensuring that venting,-ti
- perforted, will be periorsed properly. ,
The staff did consider occupational exposure, but concluced that it would be negingible since nest of the sodifications would be external to the containment.
- 9. Page'9 questions the benefit of the hardened vent for ATWS secuences.
Responses No benefit was given for prevention of ATWS sequences in the-regulatory analysis.
- 9. Page 10 discusses the interaction of various incrovements and essentially Indicates that the benefit of the improvetents depends on other improvements.
Responset We strongly agree that the taprovements overlap and interact in a complex sanner. That is the reason we considered all taprovements>together-and performed a sensitivity study on the cenefit of,the=other leprovements, given the existence of-'a hardened vent. _The sensitivity of-the benefit of a vent, given
.the other improvements was not explicitly performed, but.would not impact the conclusions since the primary benefit of venting is' prevention of-the TW sequence for which ADS is assumed to
. function and water'is available to-the vessel.
s 10.. Page 11 discusses alternative ways-to. reduce risk from the TW sequence.
k-ResponsetL!aproving existing procedures and hardware-for. venting appears-Ltc be the least -costly aethod of preventing a TW sequence < and hat-other benefits. However, the staff would be willing to-evaluate alternative means that a licensee say propose to meet the intent of this backfit.
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