ML20055E302

Forwards Backfit Analyses for Plant Re Installation of Hardened Wetwell Vent,Per Generic Ltr 89-16

ML20055E302
Person / Time
Site:	Oyster Creek
Issue date:	06/15/1990
From:	Murley T Office of Nuclear Reactor Regulation
To:	Fitzpatrick E GENERAL PUBLIC UTILITIES CORP.
References
GL-89-16, TAC-74875, NUDOCS 9007110272
Download: ML20055E302 (40)

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. NUCLEAR REGULATORY COMMISSION-

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June 15. 1990 m

Docket-No. 50-219' o

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. Mr. E; E. Fitzpatrick

.Vice President and Director 5

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<'y Oyster Creek Nuclear Generating Station 1

Post.0ffice Box 388-E

Forked River,. New Jersey 08731 2

Dear. Mr. Fitzpatrick:

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SUBJECT:

STAFF'S BACKFIT ANALYSES FOR OYSTER. CREEK NUCLEAR GENERATING

-l STATION'REGARDING INSTALLATION OF A HARDENED WETWELL VENT i

(GENERIC LETTER 89-16) (TAC NO. 74875)

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In SECY 89-017, " Mark I Containment Performance Improvement Program," of -

-January 23, 1989,'the: staff demonstrated that hardened wetwell venting capabilities at Mark I containments would prevent majority of severe

. sequences) quences involving loss of decay heat removal capability (TW accident se from resulting in core melt. The staff also~ demonstrated that s

Lventing 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 a core melt would be-i trapped-in the suppression pool.and.would not be available for release to

the environment. Some benefits are also expected because of the prevention

.of severe, accident-sequences other than TW sequences from resulting in core melt. Based on the analyses in SECY 89-017, the staff informed the Comission i

that the generic installation of hardened vent capabilities at Mark I contain-ments would provide significant'added benefits resulting from a reduction of

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severe accident risks to public health and, safety.

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- On July 11, 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)

L with Mark I: containments. Accordingly, on September 1, 1989, the staff issued f

L Generic Letter 89-16 -(GL 89-16).

In that letter, the staff urged the affected I

licensees to voluntarily install hardened vent capabilities at their Merk I containments using the provisions of the Comission's rules in 10 CFR.50.59.

'If~the licensees chose not to: install the hardened vent capability on a H

voluntary basis, the staff requested in GL 89-16 that the licensees provide L

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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.c Mr. E.'E. Fitzpatrick June 15, 1290 By letter of October 30, 1989, you responded to GL 89-16 indicating that

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you had decided not to commit to install hard vent capabilities on a voluntary basis._ You also provided the staff with plant-specific cost estimates for modifications at the Oyster Creek Nuclear Generating Station (0yster' Creek).

.Following the receipt of your October 30, 1989 letter, the staff initiated plant-specific backfit analyses for Oyster Creek.

In its analyses, the staff-used the plant-specific cost estimates that you provided. The staff estimated the benefits of venting by determining the reductions in core damage frequencies (CDFs) for only the TW sequences. The benefits were calculated by using the results of the probabilistic risk assessments (PRAs) for BWRs with Mark I containments and isolation condenser systems (ICS) similar to Oyster Creek.

The staff.then adjusted the analyses to 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 the Oyster Creek can be reduced by 1.4 E-5 per reactor year.

The credit for the operation of the ICS was included in-the analyses. The analyses were' adjusted to account for the power levels i

of Oyster Creek and the density of population surrounding the Oyster Creek site. The staff has calculated that for TW sequences alone, the operation of the vent would avert the expected radiological exposure to public by 55.4 man-rem per reactor year.

Using 19 years of remaining plant life for Oyster Creek, the staff has estimated an averted radiological aopulation exposure of 702 man-rem per million dollars for Oyster Creek. T1e preceding results of the staff analyses demonstrate that hardened vent capabilities would provide significant benefits in the expected reduction in radiological exposure risks posed.by TW-_ sequences.

The staff has also calculated the averted costs, to clean the site surroundings and to replace the lost power, that would be associated with severe accidents involving TW sequences. Assuming that the modification costs would be offset

'by the averted costs of cleaning the site surroundings and replacing power, the staff estimates that 796 man-rem will be averted per million dollars j

for Dyster Creek.

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The staff has considered but not quantified the reduction in risks posed by i

(1) severe accidents other than TW sequences, and (2) scrubbing of the j

fission products in the suppression pool for accident sequences that result in significant damage to the core. These benefits along with the benefits cf reduction in CDF caused by TW sequences provide justification to support l

the backfit in accordance with the Commission's rule of 10 CFR 50.109. A copy of the staff's supporting analyses for Oyster Creek is enclosed for your information.

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!!n'. light of the staff's backfit analyses, the staff urges that you reconsider your decision: and comit to install-a- hardened vent capability-at Oyster Creek.

L, You are requested to. inform the staff of your intent within 30 days of receipt of this letter.- You may implement your comitment under-the provisions of the Comission'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 -

i to pursue.the imposition of this backfit under the= provisions ~of the.

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Comission's backfit. rule in 10 CFR 50.109.

Sincerely, Original signed by f

l Thomas E. Murley, Director.

Office of Nuclear Reactor Regulation

Enclosure:

Plant-Specific Backfit Analyses for Oyster Creek n

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Mr. E. E. Fitzpatrick Oyster Creek Nuclear

_ 0yster Creet t!uclear Generating Stetion Generating Station M

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Ernest L. Blake, Jr.

Resident inspector "Shaw, Pittman, Potts.and.Trowbridge c/o U.S. NRC

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Post Office Box 445 1

E,.N ' 2300 N Street, FW Washington, D.C.

20037 Forked River, New Jersey 08731 J

J.B. Liberman, Escuire Comissioner

. Bishop, Liberman; Cook, et al.

New Jersey Department of Energy-1155 Avenue of the Americas 101 Comerce' Street

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.New York, New York ::10036 Newark, New Jersey 07102 l

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Kent Tosch, Chief Regional Administrator, Region 1 New Jersey _ Department nf Environmental:

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.U.S. -Nucleer Regulatory: Comission Protection J475 Allendale Road Bureau of Nuclear Engineering

. King of Prussia, Pennsylvania 19406 CN 415 Trenton, New Jersey- 08625 BWR Licensing Manager i

' GPU Nucleat Corporation

1. Upper Pond Road-Parsippany, New Jersey 07054'-

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~ Lacey Township 818 West Lacey' Road

, Forked River. New Jersey 08731

'OcensingManager L

' Oyster Creek Nuclear Generating Station

-Mail'Stop: Site Emergency Bldg.

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0. Box 388 Forked River, New Jersey 08731 s

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Plant-Specific Analysis for the oyster creek Nuclear Generating Station, Regarding j

Installation of a Hardened Vent

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TABLE 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....................................... 5 2.3 Cost-Benefit Analysis....................................... 6 2.3.1 Cost Estimation.....................................

6 12.3.2 Value-Impact Assessment.............................. 6 f

2.4 Alternatives Considered and Impacts on other Programs......

7 2.5 Environmental Assessment...................................

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.3.0 Conclusions and Recommendations..............................

8 3.1 Rationale for the Recommendation............................ 8 4.10 References................................................... 10 Appendix A.

Regulatory Analysis on the'Backfit of Hardened Vent I'

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Plant-Specific Analysis for the Oyster Creek Nuclear Generating Station, Regarding Installation of a Hardened Vent i

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.

The staff began this effort with the premise that there may be generic severe accident challenges to each light water reactor (LRR) 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 LWR containments (for example, Mark I) to successfully survive some severe accident challenges, as indicated by NUREG-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 oignificantly reduce plant risk.

This vent capability has long been i

recognized as important in reducing risk caused by loss of long-term decay 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 net positive suction head, and the re-ci'osure of the l

valves in the Automatic Depressurization System (ADS).

Venting of the containment is currently included in the emergency operating i

procedures for boiling water reactors (BWRs).

A vent path using existing containment penetrations currently exists in all Mark I o

l 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 l

under~high-pressure conditions created either before or after core celt may fail this ductwork, release the containment atmosphere into l

l the reactor building, and potentially contaminate or damage equipment needed for accident recovery.

In addition, with the existing hardware and procedures at some plants, it may not be possible to cpen or to close the vent valves for some accident scenarios.

Therefore, venting through a sheet metal ductwork path, as currently l l

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e implementedLatLsome Mark I plants, is likely to homper or-complicate p3st-accident recovery activities, and is, therefors,. viewed =by the octaff as reducing the safety benefit.

A hardened pipt ventLeapable

.of withstanding the: anticipated pressure loading of a severe' accident wculd eliminate'this disadvantage.

-The Commission concurred with the staff's position and air'ected the ctaff 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 4

centainment~.- For licensees'who, on their own initiative, elect to incorporate this: plant improvement,'the staff was directed to censider installation of a hardened vent under the provisions of c10 CFR.50.59.- For the other licensees who do not intend to install a ahtrdened vent voluntarily, the staff was to perform a plant-specific backfit analysis'for-each of these Mark I plants to evaluate the:

efficacy of requiring the installation of hardened vents.

The staff issued Generic Letter (GL) 89-16 dated September 1,.1989 (Reference 5) to BWR licensees.with Mark I containments: (1) to.

~ inform-them;of=the direction given by the Commission regarding the herdened 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 provida 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

.nst electing to voluntarily install hardened vents, the staff o

rcquested.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.

E the. commission's directive.

This program. plan contains'the following five' tasks: (1) costiestimation, (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-

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cpecific backfit analysis performed by the staff for the.0yster creek

. Nuclear Generating Station.

This analysis. complies with the backfit-l rule-in 10 CFR 50.109 (Reference 6) and includes an assessment of the

'ecfety. benefits, an estimate of the reduction in core damage i

frequency and public: risk, and a cost-benefit analysis.

From the results of this analysis, the staff concludes that the installation

of-a hardened vant capability will substantially increase public cafety and-that the results of the cost-benefit analysis support the

irplementation of the capability.

2.1 Safety Benefits

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p, The major benefit ofL a: hardened vent is the reduction of both 'the a.

core damage frequency'and'public risks.

Probabilistic Risk

. ;F ' Assessment- (PRA) studies: for BWRs indicate that' accidents initiated L'

by transients dominate the total core damage frequency.(CDF) in COvere accident, sequences.

The principal accident sequences for BWRs i

censist of Loss of Long-Term Decay Heat Removal (TW), Station Blackout- (SBO),t and-Anticipated -Transient Without Scram. (ATWS)'.

The R0 actor Safety Study (WASH-1400) (Reference 7) indicated that 1Wiis the dominant accident sequence' causing-core damage at the Peach Bottom Atomic Power Station. Further, draft NUREG-1150 (Reference 2) indicates that SB0: Is:the, dominant contributor to core damage frequency at Peach Bottom.

At Peach Bottom, it was estimated that-the TW frequency has'been greatly reduced because of the successful inplementationiof containment venting procedures._This study

'j indicates that venting, if properly implemented, can significantly.

-increase safety.

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-In SECY 89-017,_ the staff-concluded on a generic basis for Mark I plants that the-proposed hardened vent capability would provide onhanced plant capabilities with regard to both accident prevention ond mitigation.

A core melt, combined with reactor vessel rupture cnd containment failure, would release significant amounts of fission t

products to the environment.

The addition of a hardened' vent (1)

. prevents the majority'of loss of long-term decay heat removal ccpabilityLsequences (TW).from resulting.in_ core melt,_and (2) aitigates the consequences _of residual sequences involving core melt where venting through'the suppression pool is found necessary..The i

"TW sequences <are initiated by transient events and followed by J

foilure of long-term decay heat removal; the containment fails from

'overpressurization'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 nelt occurs before containment failure, venting could*be offective in' delaying containment failure and in mitigating the rolease of fission products because venting through the' suppression pool would' provide significant scrubbing of particulate and volatile-roleases.

.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 i

ccvare accident conditions could result in failure of the ductwork and a direct release of radioactivity into the reactor building.

The discharge.of high-temperature gases over an extended period of time cay-threaten the availability or performance of safety-related 1 r '. b u

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Ifl substantial fuel damage: has: occurred, the discharge, of :

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hydrogen could cause hydrogen burns-(orfdetonations) inside the-e Lrcactor building.- Electrical' cables,7 motor. operators-on valves, P

rolays, and control room: components may fail under these Etnvironmental conditions.

Adverse-environmental conditions would complicate entry into-the-reactor-building..This environment of high temperature and perhaps radiation could hamper recovery efforts by l preventing personnel from entering into the reactor building if cystems needed to terminate the accident need repair.

As a result, when relying on the existing ductwork,1the benefits of containment u1, 2 venting ato significantly uncertain.'Therefore,. hardening the vent path-to withstand-the anticipated pressure loading during a severe

' cccident would eliminate this' disadvantage while retaining all the

' benefits of containment venting.

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'Because,of the reduced core melt frequency, reduced fission product ~

R releases, and possible reduction or elimination of a significant containment failure mode, the staff concluded'that the safety

' benefits of venting are significant, and further improvement can be D

.cchieved by installing hardened' vents.

In Reference 8, theestaff q

'cstimated-the benefits in the reduction in CDF and in offsite risk, 1

q; which are< discussed 11n the'following. sections.

2'.2;. Reduction in core Damaae Frecuency and Public Risk To. estimate the plant-specific reduction in CDF,:all Mark I plants u

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!were categorized into several groups based on~the similarity of the b

idesign features that are important to the accident-sequences that could be affected by the installation of a hardened vent.

In pL performing the: analysis, the staff used existing Mark.I PRAs along-(with the plant similaritysassessment to estimate the reduction in CDF for each group of plants.. Thel analysis includes only the: change in the: core: melt frequency for the TW sequence.

2.2.1 Plant Similarity Assessment

• lIn' draft NUREG/CR-5225"(Reference 9), the three accident sequences-that!were identified-as being affected by-venting are: (1) Loss of Long-Tern Decay Heat Removal.(TW), (2)- Anticipated Transient Without Scram ;(ATWS)', and (3) Station. Blackout.(SBO).

Among these sequences, Lthe; addition of a hardened-vent was found to produce'the. greatest reduction in core damage frequency (CDF)-through its effect on TW' 7

L Lcequences.

In the TW sequence, failure to remove decay heat

' :following a transient will cause the gradual pressurization of the i

containment.

The containment may fail from overpressurization and ut cubsequently may lead to a. core melt.

In this sequence, venting can be used to allow the removal of long-term decay heat from the containment ~through pool boiling and, therefore, reduce the

. likelihood of containment failure and subsequent core melt.

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L-design features important to this sequence are the systems used for

' decay heat removal and containment cooling.

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'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 thei'r decay heat removal and containment cooling systems - factors important in assessing 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 cervice water systems for all Mark I plants.

In addition, the staff otudied the available PRAs and failure probabilities of related components to identify any major differences and similarities in terms of CDF affected by the hardened vent capability.

After careful tudy of the available PRAs, the staff categorized the Mark I plants into the following four groups:

(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) Plants with an RHR consisting of two trains, with one RHR heat exchanger and two RHR pumps per train, (3) Plants with an RHR consisting of two trains, with one RHR heat exchanger and one RHR pump per train,.and (4) Plants with isolation condensers.

2.2.2 Reduction in Core Damace Frecuency To estimate the reduction in CDF from the installation of a hardened vent capability, the staff looked into the sequences that require the failure of containment cooling for coro damage, and assumed that using hardened vent would reduce 90 percent of these sequences..The

'astimates of CDF reduction conservatively cvnsider only the TW

' sequences, and therefore, the benefits on the SBO and ATWS sequences are not included.

For Oyster Creek, the reduction in CDF was estimated using the PRA results of a plant with similar design features.

The credit of the Icelation Condenser System (ICS) being used as the decay heat removal system was included.

To be consistent with the failure frequency assumed in NUREG-1150, the staff incorporated several changes into the referenced PRA.

With these changes, the staff calculated that venting would produce a reduction in CDF from TW sequences of 1.4E-5 per reactor year.

More detailed information of this analysis is - -

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i givenLin' Reference 8.ni 22.2.3 Risk' Reduction-Installation of;a hardened-vent capab'ility will reduce the CDF and

.will result:in a reduction in the. population dose that would be ccsociated.with TW sequences.

The estimate.of the reduction'in population dose 1for oyster Creek was calculated by multiplying the r:ductioniin CDF estimated forz Oyster Creek by a scaling factor to q

convertLthe Peach Bottom. population dose to the Oyrter Creek pspulation; dose.

The scaling-factor was obtained trom'NUREG/CR-2723 l

1(ReferenceL10) for Oyster Creek plant-specific reactor power and-1

,p:pulation density.

The Peach-Bcttom. population dose:from TW 00guences:was:darived.using the insights from NUREG-1150.

The rssulting: reduction in the. population dose' for oyster Creek due to r: duction in CDFifor TW sequences was~ estimated to be 3.96E6 man-i

.r m.1The averted. population dosoffor oyster Creek was calculated by Luultiplying the reduction in~CDF by.3.96E6 man-rem to give 55.4 man-1l aren.per-reactor' year.- For the,19 years of-operation remaining, the

.octimated total avertad dose is 1053 man-rem.

In addition, f

consideration:of a,likely.20-year operating life extension will.

increase the estimated: total averted' dose to 2161 man-rem.

The: averted occupational health risk resulting from the installation L

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of.the proposed hardened vent system is discussed ~and calculated in.

Scction.4.1.2.2-of Appendix A.

The estimated occupational risk is

-cpproximately one to two percent of the public health risk and is not-csnsideredlto be a'significant contributor..Therefore, the L

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Leccupational. health exposures are not further considered-in the cost-l

banafitEanalysis.

f 2,3--cost-Benefit Analysis b

The methodeused to calculate the' cost-benefit ratio is described in i

L NUREG/CR-3568 (Reference 11), and the plant-specific data were c:nsidered.

The staff obtained plant-specific-cost estimates L

provided by the licensee from the response to Generic Letter (GL) 89-16: and used-the risk-reduction data-discussed above in Section 2.2.3 1 to calculate'the value-impact ratio in man-rem saved per million dollars.

. 2. 3.1L Cost Estimation L

L LGLL89-16: requested licensees to provide the staff with. plant-specific

cost" estimates for: installing a hardened vent.

In response to GL 89-116, all Mark I licensees except four (with five plants) have E

indicated that they will install the hardened vent under the k

provisions of 10 CFR 50.59.

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Oyster Creek is one of the five Mark I plants, GPU Nuclear.

Carporation (the licensee) has decided not to voluntarily install the h2rdened vent capability.

By Jetter dated October 30, 1989 (Reference 12), the licensee responded to GL 89-16 with two cost C3timates..The staff used.the estimate of 1.5 million dollars for

~the installation of a hardened vent and incremental costs of $600,000 l

for an AC independent power source.

This is the lower one of the two i

cotimates provided by the licensee.

The other estimate was based on the future dollar, which the staff determined not proper for the cost-benefit analysis.

Even this lower estimate is relatively high compared to the other licensee's estimation.

The licensee stated that the major cost components included the distance and route of the vcnt path, the reactor building penetration, length of cable and conduit running to the control room,.and the engineering of radiation nonitoring and hydrogen combustion control features.

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2.3.2 Value-ImDact Assessment

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The value-impact ratio is calculated in the regulatory analysis (Appendix A) using the method described in NUREG/CR-3568 (Reference

11) to support-the backfit decision.

The benefits to public risk rcduction in man-rem were calculated in-Section 2.2.3.

The averted population dose for Oyster Creek was calculated in Section 2.2.3 to a

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.b3 55.4 man-rem per reactor year.

For the 19 years of operation remaining, the estimated total averted man-rem is 1053.

The cost of l

installation of the hardened vent capability was estimated in Section L

2.3.1 as'1.5 million dollars.

The value-impact ratio, not including i

the averted onsite cost, is calculated to be 702 man-rem saved per l

-nillion-dollars.

The averted cost associated with prevention and mitigation of an cccident can-be discussed as five separate costs: replacement power, cleanup, onsite occupational health impacts, offsite-health impacts, and'onsite property damage.

The details of each of these items are t

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discussed in Appendix A'Section 4.1.2.2.

If the savings of $177,313 to Oyster Creek from accident avoidance-(cleanup, repair of onsite

~ damages, and replacement power) were included, the overall value-inpact~ ratio would be'796 man-rem saved per million dollars.

Consideration of a likely 20-year operating life extension will increase the value-impact ratio to 1667 man-rem saved per million dollars.

2.4 Alternatives Considered and ImDacts on Other Programs l

Other alternatives considered and their associated value-impact L

ratios are discussed in Section 3.0 and 4.0 of the Regulatory l

Analysis in Appendix A, Regulatory Analysis.

The effect of the

' addition of the hardened vent capability on other requirements

' including IPE, Improved Plant Operations (IPO), Severe Accident -.

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h IR0 search ProgramL(SARP), External Events, and Accident Management:are

discussed in-Scotion 4.2

of Appendix A.

A summary of the. compliance

>j PE p to: the 'backfit' rule -(10: CFR-50.109 (c)) is also included in' Attachment jf

>!;fl1.to Appendix A.

u j 2.5.

Environmental Assac. ament y

The staff _ performed a generic environmental assessment (EA) 3 7

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,q es "k icencerning the installation of the hardened vent at Mark I plants, j

' (Cancurrent_with this plant-specitic analysis, a draft EA is being_

(cOntEout for public comnents.

In the draft EA, the staff concluded-that the~ installation of a hardened vent' capability will have no l

wicignificant radiological'or non-radiological impact.on the

?cnvironment._

0TheJihatallation of the hardened vent capability will prevent and i

saitigate severe accidents., During normal plant; operations or design-bnsis accidents, the hardened _ vent will not be used,'and therefore, J

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[will not result in.any changes in amounts of radioactivity released to:the atmosphere from the plant.

Venting during severe accidents-4 s

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. will reduce'the CDF.and will reduce the= radiological environmental-N risks. :For. venting sequences, the hardened vent connected to the 1

plant. stack 1could reduce dose consequences more effectively by

cpproximatelyna factor of two than venting through?the ductwork.

This reduction is due to a greater effectiveness of atmospheric

,4 dispersion resulting-from a controlled elevated release as. compared j

to ansuncontrolled. ground: level release from'ductwork.

Furthermore, i

-venting through the suppression pool would provideLscrubbing of non-C Enoble-gas-. fission products with an effective decontamination factor Jofiabout!100.

The addition of a hardened. vent wi11' greatly reduce 1

"E he: occupational' doses for personnel.that need to enter and work in t

g L"

the reactor building and that could be exposed-to the. containment

,Lcnvironment.

L L

IThe staff has concluded that this generic EA appliss to oyster Creek L

cnd the installation of the hardened vent will rcduce dose H

.. consequences and.will not result in an adverse environmental impact.

Plant-specific design features will have an.effect on the degree of the. environmental benefits, but not on the conclusion concerning no oignificant environmental impact.

13.0 conclusions and Recommendations Based on the safety benefits discussed in Sections 2.1, 2.2, and 2~.3 1

a.

for oyster Creek and in SECY'89-017 for generic Mark I plants and cupported by the plant-specific cost-benefit analysis, the staff f

believes that.the installation of a hardened wetwell vent at Oyster

' Creek'is warranted.

.1 L 1

- - -~-_ _ _.-

\\

s 3.1 Rationale for the Recommendation In SECY 89-017, the staff concluded on a generic basis for Mark I plants that the proposed hardened vent capability would provide onhanced plant capabilities'with regard to both accident prevention cnd mitigation.

The addition of a hardened vent (1) prevents the nojority of TW sequences from resulting in core melt, and (2) mitigates the consequences of residual sequences involving core melt where venting through the suppression pool is found to be necessary.

In TW sequences, the containment fails before the core melt occurs; l

therefore, significant releases could result.

A core melt, combined with a reactor vessel and containment failure, would release The oignificant amounts of fir sion products to the environment.

curvivability of the conte.inment, which acts as the last barrier for on uncontrolled release of radiation, would increase with venting.

The installation of a hardened vent greatly reduces the likelihood of c core melt from TW sequences and therefore reduces the risks to the l

For other sequences where core melt is predicted, venting public.

could be effective in delaying containment failure and in mitigating the release of fission products. Although venting of the containment io currently included in BWR emergency operating procedures, it ganerally uses ductwork with a low decign pressure.

Venting under high-pressure severe accident conditions could fail this ductwork, rolease the 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

.as reducing the safety benefit.

The installation of a reliable 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 satinated that the total plant CDF for Oyster Creek can be reduced by l

1.4E-5 per reactor year because of the reduction in the probability of TW sequences.

Implementation of the proposed hardened vent nodification will significantly reduce the total risk to the health and safety of the public.

The averted population dose of 55.4 man-l rem per reactor year was calculated for oyster Creek from the installation of hardened vent capability.

For 19 years of remaining I

operating life the total averted population dose would be 1053 man-If the averted cost associated with an accident is included, rem.

the calculated value-impact ratio for Oyster Creek is 796 man-rem l

gaved per million dollars.

In addition, consideration of a likely 20-year operating life extension will increase the total averted population dose to 2161 man-rem and the calculated value-impact ratio to 1667 man-rem saved per million dollars, which demonstrate additional benefits for the installation of the hardened vent capability.

Additional benefits of venting, not quantified, include

_9_

9 l

C^urce term reduction and the delay in containment failure for some-Cf'the scenarios that lead to core malt.

t Based on both the qualitative and quantitative benefits discussed hOrein and the supporting plant-specific cost-benefit analysis, the ctaff believes that there will be a substantial increase in the

.overall protection of the public health and safety by~ implementing l

~the hardened vent canability for Oyster Creek.

Therefore, the staff believes that this backfit is justified.

i y.

b e

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i t

11; 1

4.0 Es.Lanssa I

L 10 SECY-87-297s U.S. NRC, " Mark I containment Performance Program Plan,"

V. Stallo to NRC Commissioners, December 8, 1987.

l t

2.

NUREG-1150, Second Draft, U.S. NRC, " Severe Accident Risks: An 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 23, 1989.

4.

. Memorandum from S. J. Chilk to V. Stello, "SECY-89-017 - Mark I Containment Performance Improvement Program," July 11, 1989, b.

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.

7.

WASH-1400, 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.

i 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.

{

12.

. Letter from D.K. Groneberger (GPU Nuclear Corporation) to U.S.

NRC, October 30, 1989, "Oystar Creek Nuclear Generating t

Station Response to Generic Letter 89-16, Mark I Containment Hardened Vent."

c

!n ' :o Appendix A f

i 3

e t

l' l

t h

[ '.

MARK I PIANT-SPECIFIC ENHANCED VENTING CAPABILITY REGU!ATORY ANALYSIS g

I FOR OYSTER CREEK NUCLEAR GENERATING STATION b

k E

{

l I

1 1

(-

l l

l 5

e i

i

.. ~.. -....

i d

I i

1 l

TABLE OF CONTENTS i

1.0 STATEMENT OF THE PROBLEM...............................

A-1 2.0 OBJECTIVES............................................

A-2 A-2 3.0 ALTERNATIVE RESOLUTIONS...............................

A-2

]

3.1 Alternative (i)

A-3 3.2 Alternative (ii)

A-4 1

3.3 Alternative (iii) i A-4

)

4.0 CONSEQUENCES..........................................

4.1 Costs and Benefits of Alternative Resolutions.......

A-4

)

A-4 4.1.1 Alternative (i)

A*

4.1.2 Alternative (ii) 4.1.2.1 Values Risk Reduction Estimates.......

h-c 4.1.2.2 Impacts: Cost Estimates...............

A-5 1

4.1.2.3 Value-Impact Ratio....................

A-7 4.1.3 Alternative (iii)

A-7 4.1.3.1 Value Risk Reduction Estimates.......

A-7 J

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 4.3 Constraints......................................... A-12 5.0~ DECISION RATIONALE.................................... A-12 5.1 Commission's Safety Ooal............................ A-12 i

l 6.0 IMPLEMENTATION........................................ A-12 6.1 Schedule for Implementation......................... A-12

7.0 REFERENCES

............................................ A-14 ATTACHMENT 1 TO APPENDIX A - BACKFIT RULE ANALYSIS......... A-15 i

l l-L l

4 l

L=

i

)

l Mark I Plant-Specific.

-i Enhanced Venting Capability Regulatory Analysis 1.0 STATEMENT OF THE PROBLEM In SECY-89-017 dated January 23, 1989 (Reference 1), the staff f

presented its findings concerning the Mark I Containment Performance i

Icprovement (CPI) program to the Commission.

One of the improvement that the staff recommended was the installation of hardened vent l

capability.

The Commission concurred with the staff's position and i

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 c:nfigurations with three basic containment designs designated as l

Mark I, Mark II, and Mark III.

Probabilistic Risk Assessment (PRA) ctudies.have'been performed for a number of BWRs with Mark I r

f ogntainments.

Although these PRA studies do not show the BWR Mark I plants to be risk outliers as a class relative to other plant d3 signs, they do suggest that the Mark I containment could be challenged'by a large scale core melt accident, primarily due to its

.craller size.

However, estimates of the probability of containment 1

foilure under such conditions are based on calculations of complex cccident conditions that contain significant uncertainty.

Draft NUREG-1150 (Reference 2) evaluated the dominant accident c quences 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 power; and enticipated transient without scram (ATWS). This list would have included the loss of long-term decay heat removal (TW) except that, c

for the particular plant being reviewed, the likelihood of this coquence was considered to be greatly reduced because of assumed j

-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-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 casociated with the vent and purge system used to inert and de-inert containment.

Venting of containment as an accident mitigative action

.is permitted in the Emergency operating Procedures (EOPs).

In part, A-1 1

5

-e

~a

L f

j the existing vent path uses sheetmetal ductwork from the containment I

icolation valves through the standby gas treatment system (SGTS) to the plant stack.

The sheetmetal ductwork is usually designed for low pressure and is expected to fail under severe accident pressures.

L l

Foilure of the ductwork would introduce the containment atmosphere to the reactor building.

This could result in harsh environmental 3

L conditions that would complicate operator accident recovery _ actions

- within the reactor building and could cause failure of equipment

- within the reactor building.

The hard pipe vent would be designed to withstand severe accident

. pressures, and,=thus, would not fail during a TW event thereby olleviating the harsh environmental concerns in the reactor building.

This regulatory analysis studied the costs and benefits of installing o hardened vent capability at BWRs with Mark I containments.

?

2.0 OBJECTIVES 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 Ond return the plant to a controlled, safe state, and (2) accident citigation - 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 concerning both accident prevention and mitigation.

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 watwell ventilation penetration, bypassing the ductwork to the standby gas

- treatment system, and going to the plant stack.

The ventilation penetration is the 18-to 24-inch penetration normally used as part ef 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 required for coping A-2 6

w

.. _. -,-e_.

,._________m m

with design-basis accidents.

3.1 Alternative (i)

This alternative is the no-action option, that is, to leave the cxisting venting capability unaltered.

The existing venting capability vents the containment through the cxisting ductwork from the suppression pool to the SGTS.

The ductwork design pressure is usually a few psid or less (Reference 3).

Ccnsequently, venting under severe accident conditions could cause i

failure of the ductwork and a direct release into the reactor building.

The discharge of high-temperature gases over an extended pariod 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 control room componente may fail under these environmental conditions.

Adverse environmental conditions would complicate entry into the I

rcactor building.

calculations from a venting study during an onticipated transient without scram (ATWS) indicate a severe Cnvironment 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.

3.2 Alternative fli)

This alternative would involve the installation of a hardened venting ccpability from the containment wetwell to the plant stack.

The proposed venting improvement would provide a vetwell 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 watwell vent outboard containment isolation valve to the basa of the plant stack.

This pipe would be routed through a new Asolation valve i

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 wsuld need to be modified to provide appropriate instructions for the cperator.

This alternative would mitigate the consequences of severe Occidents by reducing the likelihood of core melt from the TW ccquence.

All releases through the vent would pass through the I

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 the vent path inside the reactor A-3

p i

?

L;-

?

building and would result in an elevated release.

The elevated rOlease could reduce the offsite consequences.

Since the vent path

(

, 'chould-not fail inside of the reactor building, personnel could p

r; pair equipment and perform other plant recovery activities in the-M r0 actor building.

Furthermore, there would be no harsh environmental J

L

c:nditions to degrade or fail other equipment.

There is the j

I' p;ssibility of inadvertent operation of the vant that would release l

ccme radioactive material without any holdup time or filtration.

1 This alternative would not affect the releases of radioactive i

I' notorial for those sequences where the drywell fails, such as from ocrium' attack, once the drywell shell has failed.

1

- 1 J

-3.3 Alternative Qiil q

This' alternative would involve alternative (ii) plus the instal-1ction of an external filter system.

]

[

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

,' 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 Filtra and the MVSS systems do not rely en'AC power to perform their intended functions.

Similar to alternative (ii), the emergency procedures would need to be modified to: provide appropriate instructions for the operator.. This citernative would mitigate the consequences of a severe accident and 1

could reduce the likelihood of core melt if the operator. transfers f

cuction of the injection pumps from the suppression pool to an citernate 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 externa 1' 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 f

Lexternal. 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),

-this alternative would not affect the releases of radioactive

-satorial for those sequences where the drywell fails, such as from corium attack,.once the drywell shell has failed.

4.0 CONSEQUENCES 4.11 costs and Benefits of Alternative Resolutions f

A-4 9

-,.,w.

.,_a-,-,

---+,w.,

..,,w,-,n-,n e,

a,,,.

<_,-.,-,,.m,,-,,,,,----,-,,m-,--n,-nm,-v,-e,,,

The' staff used available PRAs to estimate the incremental benefit of the three alternatives discussed in the following paragraphs.

The i

cnly accident sequence that is being considered for this analysis is

)

the TW.

This is considered to be conservative since the alternatives csuld have a beneficial but small effect on other sequences (Reference 5). The staff estimated the change in the CDF, but not the tttal CDF from internal events (Reference 6).

p:

4.1.1 Alternative til This alternative would be to take no action.

Since it is expected s

that the ductwork would fail if the containment were vented at high pressure, this approach would not only jeopardize personnel, but also

-the ability to' regain control of the facility during the accident.

L 4- ;Furthermore, based on a generic regulatory analysis-(Reference 1) the Commission instructed the staf f to require hardened vent capability fer plants for which it could be shown to be cost effective.

.Therefore, based on the discussion below the no-action alternative is not recommended.

4.1.2 Alternative 4,1),

4.1.3.1 values Risk Reduction Estimates i

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 1.4E-5.

Corresponding to a release of 3.96E6 man-rem, this represents a risk reduction in man-rem per reactor year of 55.4.

4.1.2.2 Impacts: Cost' Estimates The estimated cost for installation of the hard pipe vent path is 1.5 million dollars (Reference 7).

The averted cost associated with prevention and mitigation of an accident can be discoeced as five separate costs:

replacement power, cleanup, onsite occupctional health impacts, offsite health impacts, and onsite property damage.

To estimate the costs of averting plant de. mage 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:

1.

V, = NdFU

.U - (C/m) ( (e'"")) /r') (1-e*""O*"i")

( 1-e"*)

A-5 l

m

.,,,,,,. -, - + - -. -,

'y e

f where: (cited values are from Table 2)

V,,

= value of avoided onsite property damage ($)

N

= number of affected facilities = 1 dF

= reduction in accident frequency = 1.4E-5 /RY U

= present value of onsite property damage ($)

C

= cleanup and repair costs = $1.0 billion t(f) = years remaining until end of plant life = 19 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 Using these values, the present value of avoided onsite property damage is estimated to be $75,261.

Replacement power costs can be estimated using NUREG/CR-4012 (Reference'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 generic replacement power cost is $400,666 per day.

(Tn= plant-specific replacement power cost is shown in Table 3.

NUREG-1109 (Reference 10) used a generic cost of $500,000 per day and compares favorably with

(

NUREG/CR-4012.)

The change in public health risk associated with the installation 1

of the proposed hardened vent system is expressed as total man-rem of avoided exposure.

The following equations from NUREG/CR-3568 i

were used to make this calculations V, = NT ( D, x R)

I p

l where L

v,

= value of public health risk avoided for net-p benefit method ($)

N

= number of affected reactors = 1 l'

T

= average remaining lifetime of affected facilities L

(years) = 19 l-D,

= avoided public dose per reactor-year (man-rea/RY)

I'

= 55.4 R

= monetary equivalent of unit dose ($/ man-rem)

= $1000 Using these values, the avoided public health exposure of 1.053 million dollars is obtained for oyster Creek.

Considering a possible 20-year operating life extension, the value of avoided public health exposure is 2.161 million dollars.

A-6

l l

The occupational health risk avoided because of the installation of

~

the proposed hardened vent system is expressed as man-rea of avoided exposure.

The following equations from NUREG/CR-3568 were used to make this calculationt i

l

' V,g = NT(D x R) t a

where V,, = value of occupational health risk due to accidents avoided ($)

N

= number of affected reactors (reactors) =1 T

= average remaining lifetime of affected facilities (years)

D.

= avoided occupational dose per reactor year (Han-Rem / Reactor-Year)

R

= monetary value of unit dose ($/ Man-Rem)

= $1000 / Man-Rem There are two types of occupational exposure related to accidents, immediate and long-term.

The first occurs at the time of the accident and during the immediate management of the emergency.

The second is a long-term exposure, presumably at significantly lower I

individual rates, associated with the cleanup and refurbishment of the damaged facility.

The best estimate of the immediate occupational exposure as specified in NUREG/CR-3568 is 1000 man-rom.

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 J

21,000 man-rem by the reduction in CDF, 1.4E-5 per reactor year, i

produces the-avoided occupational dose per reactor yesr, tha.

1 Using these values, the present.value of avoided occupational health exposure was calculated to be $5,586, approximately one to 1

two percent of the public health risk, and is not considered to be i

a significant contributor.

Therefore, the occupational health exposures will not be considered further.

=4.1.2.3 Value-Impact Ratio l

The value-impact ratio, not including the costs of onsite accident l

avoidance, is 702 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 796 man-rem averted per million

' dollars.

Considering a likely 20-year operating life extension, the overall value-impact ratio would be 1697 man-rem averted per million dollars.

A-7

i e

I 1

e 4.1.3 Alternative fili) 4.1.3.1 Values Risk Reduction Estimates l

This alternative-would provide minor additional particulate j

' scrubbing for the hard vent.

However, because all particulate 1

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 and about $5 million for the Multi-Venturi l

Scrubber System design.

i Using the same equations given in alternative (ii), the present-

'value of the estimated avoided onsite damage to property.is.

$75,261. 'Similarly, the estimated replacement power cost is $135.6 million per year.

Thus, the estimated avoided damage to onsite property and the replacement power is $177,313.

.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 $1.053 million.

4.1.3.3 Value-Impact Ratio I

The overall value-impact ratio of this alternative is in terms of L

man-rem averted per million dollars.

If the savings to industry

from acciden* avoidance (cleanup and repair of onsite damages and o

l-replacement power) were included, the overall value-impact ratio L

would be 166-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 N of Table 2.

This alternative is not recommended because it does not provide substantial additional safety benefit over alternative (ii) and is not cost effective.

h l

A-8 h

,,-..---,,-_c..,

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i T;ble 1 - cost Benefits of Alternatives (i)-(iii)

(man-rem averted per million dollars) i 1

Alternative (1)

- do nothing 0

Alternative (ii) - hard pipe venting for the remaining life 796 with 20-year life extension 1667 Alternative (iii) - hard pipe Aenting 166

+ MVSS external filter P

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-sporattel Seeseneet.It97et2 3-1551514 fre2*el3. IteD 9841 tem 386 46tWe I

7.. It per 9eerl espi Per 86#W-88 1

treg 4 3retw treet 19ev 19 - 3.2es,ese s.est45 e.vtsms 3.9stees 25.4 - tes2.s f.3s 7e2 s75.2s st.ss2.363 s5,3e6 st35,3se,9ee siff,313 796 :

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I 4 erster treet 1909 39 3,299,000 1.est-e5 s.92em3 3.9et+46 35.e 2340.3 1.30 teet se6,706 52.148,524 sti,ee6 st35,3se,9ee 9104,277 luf *.

e storeset rates to I analysis Sete-) 16-apr-9e 16ee ->

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61

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Ike omsters in tte toteen titles refer to seerte e4 te6erentles omster stese.

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therefore tee preweed sedification esteeds the Stegersomwee criterta and any te imposed.

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1 TCble 3 - Estimated Replacement Power Costs (in dollars per day)

Year Est. Cost Est. Cost E'st. Cost Reactor Name MWe Licensed 1985$

1989$

(per year)

Oyster Creek 650 1969

$299,600

$371,504

$135,598,960

'H5 test 1:NUREG/CR-4012.(Table S.1) provides replacement power costs for all plants on per plant / season basis for 1987-1991.

2tThe inflation rate used is 6 percent / year, and the discount

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rate used is 10 percent / year.

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4.2 Innacts'on Other Resuirements There are six programs related to severe accidents: Individual Plant Examination (IPE), Containment Performance Improvement (the topic of this regulatory analysis), Improved Plant Operations, Severe Accident Research Program, External Events, and Accident Management.

Each of tho'five-programs related to containment Performance Improvement (CPI)'will be discussed briefly in Item 3 of Attachment 1, Backfit 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 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 DECISION RATIONALE l

The evaluation of the CPI program included deterministic and probabilistic analyses.

Calculations to estimate the CDF and the consequences of the TW sequence were performed using information cvailable from the NUREG-1150 program and from existing PRAs.

i-The bast estimata of the centribution of TW to the total plant'CDF

~

l cxpressed in events per reactor year for oyster Creek is 1.4E-5.

l L

Implementation of the proposed hardened venting capability will cause TW to be a minor contributor to the total CDF and will significantly i.

L reduce the total risk to the health and safety to the public.

f 5.1 gganission*8 safety Goal on August 4, 1986, the Commission pnblished in the Federal Reaister a policy-statement on " Safety Goals for the Operations of Nuclear Power Plants" (51 FR 28044).

This' policy-statement focuses on the risks to the public from nuclear power plant operation-and establishes goals

--that broadly define an acceptable level of radiological risk.

The-discussion in the Regulatory Analysis of SECY 89-017-addressed the CPI program recommendation in light of these goals.

M, 6.O IMPLEMENTATION

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, e-6.1 - schedule for Innlementation The licensee may reconsider its position on the installation of the A-12 f

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- 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 of its receipt of this analysis, requiring this backfit under the provision of 10 CFR 50.109.

Within 60 days after issuance of the i

backfit order, the licensee will be required to submit to the NRC e cchedule for implementing any necessary equipment and procedural codifications to meet the performance goals and to provide adequate defense-in-depth.- All plant modifications are to be installed, procedures (including the. decision making process for venting) revised, and operators trained not later than January 1993.

Other schedules were considered;-however, the staff believes the proposed implementation of the hard pipe vent capability can be

' largely performed with minimum interfacing with containment and cngineered safety feature systems and thus with the plant online.

Therefore, the licensee can install the proposed modification without.

r' 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.

Shorter or less flexible Cchedules would be unnecessarily burdensome.

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7.0 REFERENCES

1.

'SECY-89-017, " Mark I. Containment Performance Improvement Program," January 23, 1989.

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Reactor Risk Reference Document',"

.2.

NUREG-1150, (Draft),

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," 1996 Reactor Water Safety Meetingt j

U Gaithersbura. Maryland, October 1986.

An Overview of Boiling Water 5.

NUREG/CR-5225, Addendum 1, Reactor Mark I containment Venting Risk Implications, An

-Evaluation of Potential Mark I containment Improvements," June 1989.

" Reduction in Risk

.6..

Sheron, B.W., Memorandum to Thadani, A.C.,

from the Addition of Hardened Vents in BWR Mark I Reactors,"

October 19, 1989.

'7.

Letter from D.K. Groneberger (GPU Nuclear Corporation) to U.S.

p NRC, October 30, 1989, "0yster Creek Nuclear Generating l

Station Response to Generic Letter 89-16, Mark I Containment 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 Statest 1987-1991," January 1987.

s 10.

NUREG-1109, " Regulatory /Backfit Analysis for the Resolution of Unresolved Safety Isr.ue A-44, Station Blackout," June 1988.

11.

SECY-88-147, " Integration Plan for closure of Severe Accident Issues," May 25, 1988.

l 12.

Memorandum from S. J. Chilk to V. Stello, "SECY-89-017 - Mark I containment Performance Improvement Program," July 11, 1989.

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ATTACHMENT 1 TO APPENDIX A t

i BACKFIT RULE ANALYSIS Analysis and Determination That the Recommended Hard Pipe Vent capability for containment Performance Improvement complies with the Backfit Rule 10 CFR 50.109 The Commission's regulations establish requirements for the design ond testing of containment and containment cooling systems (10 CFR 50, Appendix A, General Design Criteria 50, 52, 53, 54, 55, 56, and

57) with respect to design basis accident conditions.

As evidenced by the accident at TMI Unit 2, accidents could progress beyond design b0 sis considerations and result in a severe accident.

Such an occident could challenge the integrity of containment.

Existing rcgulations do not explicitly require that nuclear power plant etntainments be designed to withstand severe accident conditions.

The staff and our consultants studied this issue as part of the OGvere accident program for the General Electric Company boiling water reactors (BF9s) with Mark I containments.

BWRs with Mark I c:ntainments were c9 viewed first because of the perceived cusceptibility

ne Mark I containments to failure based, in part, en the small es: vinment volume of the Mark I containment design.

Both determinie 4c and probabilistic analyses were performed to e

ovaluate 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, containment failure, i

and risk to the public health and safety.

The risk analysis shows that the risks from plants with Mark I containments are generally oimilar to the risks from plants with containments of other types.

In addition, the hardened pipe vent capability is not needed to provide adequate protection of the public health and safety.

Rather, the proposed plant improvement will provide substantial cost-offective enhancement to Mark I plant safety.

I The estimated benefit from implementing the proposed hard pipe vent is a reduction in the frequency of core melt caused by TW and the ossociated reduction in risk of offsite radioactive releases.

The l

Cstimated risk reduction in terms of man-rem is 1053 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 cnhancement is 1.5 million dollars. This cost would be primarily for l

the licensee to 1) assess the plant's capability, 2) install Cquipment to provide additional pressure relieving capability, 3) revise the emergency operating procedures, and 4) provide operator A-15

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training concerning mitigating the TW sequence.

The estimated value-impact ratio, not including accident avoidance c:sts, in terms of man-rems averted per million dollars is 702.

If the not cost, which includes the cost savings from accident avoidance L

(i.e. cleanup and repair of onsite damages and replacement powee i

following an accident), was included, the estimated overall value-icpact in terms of man-rems averted per million dollars would be 796.

If 20 years of life extension were included, the estimated overall value-impact in terms of man-rens averted per million dollars would b3 1667.

These values support proceeding with the proposed hard pipe V0nt capability improvement.

n1though the preceding quantitative value-impact analysis was one of the factors considered in evaluating the proposed improvements, other fcctors 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 o 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 oystems required for reactor and containment heat removal are uitavailable 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 oyster Creek wts 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 cbility to cope with a TW event would substantially increase the everall protection of the public health and safety. Also, this increased protection will justify the direct and indirect costs of implementation.

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e Analysis of 10 CFR 50.109fe) Factors I

(1) statement of the specific obiectives that the backfit is desianed to achieve The objective of the proposed hard-pipe vent capability is to

' reduce the risk from TW 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 descriotion of the activity resuired by the licensee or acclicant in order to comolete the backfit 4

To comply with the proposed improvement in containment venting, the licensee will be required tot 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 vent isolation valves to be opened and closed under anticipated containment pressures and vent flow rates during severe accidents involving TW sequences.

Determine the necessary plant modifications to ensure a hard-pipe vent path will be available under TW events, develop a 1

schedule for plant modification, and submit the schedule to the NRC within 60 days from the issuance of the backfit order, h

Complete the necessary modifications by January, 1993.

l The licensee will be required to have the decision making process, i

the procedures and training to cope with and recover from a TW severe accident.

These procedures should conform to the Emergency i

i Procedure Guidelines of the Boiling Water Reactor Owner's Group.

(3)

The notential safety imoact of chances in clant or coerational l

l comolexity, includina the relationshio to orocomed and existina reaulatory resuirements i

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 l

plant, it in a simple system.

The containment performance l

improvement (CPI) program is related to implementation of the Commission's Severe Accident Policy Statement as defined in SECY-L A-17 3

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88-147 (Reference 11).

In SECY-88-147 the staff described the i

various programs underway related to closure of severe accident i

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.

l i

Individual Plant Examination (IPE)

The IPE involves the formulation of an integrated and systematic approach to an examination of each nuclear power plant in operation or under construction for possible significant plant-specific.rlsk contributors that might be missed without a systematic search.

Supplement 1 to Generic l

Letter 88-20 roguested that Mark 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 I

vessel-and for containment sprays. The examination will carefully examine containment performance in striking a balance between accident prevention and consequence mitigation.

The IPE progran 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; to expansion of the Emergency Operating Procedures (EOPs)ies; l

include' guidance on severe accident management strateg l

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

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identify potential problems early and prevent their l

occurrence.

The IPO is related to the CPI program's r

recommendation since we recommend improved procedures and operator training to use the proposed hard vent system.

. Severe Accident Research Program (SARP)

The SARP was begun after the Three Mile Island, Unit 2, (TMI-A-18

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2) accident in March 1979 to provide the Commission and the i

NRC staff with the technical data and analytical methodology' needed to address severe accident issues.

This program has i

provided input to the NUREG-1150 program and to the CPI program.

Additional research is being carried out to evaluate i

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 l

to prevent or delay shell melt by core debris.

Accident Management i

The accident management program addresses certain preparatory i

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) minimize 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 iustification 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 Implementation of the proposed hardened-vent capability is expected to result in an estimated risk reduction to the public of 1053 man-rem over the remaining plant life.

(6)

Eggential imoact on radioloaical eroesure of facility emploveta Although the reduction in occupational exposure caused by reduced CDF and associated post-accident cleanup and repair activities 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 A-19 l

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path should be negligible.

No increase in occupational exposure is

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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) 1 Data 11ation and continuina costs associated with tha backfit, includina the cost of facility downtime or the cost of construction delav Because the plant can be operating during installation, there are 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 1.5 million dollars.

(8)

The estimated burden on the NRC associated with the backfit and the availability of such resouregg 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 eualitative factors beerina on the need for the backfit at the earticular 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 accrocriate interoffice coordination related to the crocosed backfit and the olan for isolamentation 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 A-20 1'

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a 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 Dermittina imolementation 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 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 innlementation and verification of imolementation of the backfit. as amorocriate The proposed backfit is to be installed under 10 CFR 50.59 for most of plants and, thus, will require minimal staff effort.

Therefore, 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_ safety-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 crocosed niant-seecific backfit as a notential aeneric backfit Initially, the staff proposed the installation of hardened vent as a 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 generic backfit.

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