ML14058A033

Presentation to the Lessons Learned Oversight Board on Oconee Nuclear Station External Flood Protection Concern

ML14058A033
Person / Time
Site:	Oconee
Issue date:	05/05/2009
From:	Circle J A NRC/NRR/DRA
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References
FOIA/PA-2012-0325
Download: ML14058A033 (11)

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V pOconee Nuclear Station ExternalFlood Protection ConcernMay 5, 2009 presentation to theLessons Learned Oversight BoardJeff CircleDivision of Risk Assessment Office of Nuclear Reactor Regulation dcial Use 0 -SecuU ..R "ltenfor t

Background of IssueNRC initiated the Systematic Evaluation Program (SEP) in 1977 to review the designof older, operating nuclear power plants withthe current Standard Review Plan (SRP).-Opened Generic Safety Issue GSI-156.1.2, "DamIntegrity and Site Flooding".

-Oconee Nuclear Station (ONS) was identified asone such plant with flooding vulnerability.

-GSI-156 scheduled to be closed out by licensees in the Generic Letter 88-20, Supplement 4, theIndividual Plant Examination of External Events(IPEEE) program.USNRC 2-Rd I nm.t.

and Oconee Nuclear StationThree-unit site with unique flooding vulnerability.

-On Lake Keowee near Seneca, SC-No emergency diesel generators

-Reliance of 2-unit Keowee Dam as sole source emergency ac power-Site is downstream of Jocassee Dam, A 385-ft high pumped storage hydro-station holding back LakeJocassee-Licensee constructed the Standby Shutdown Facility (SSF)on site to address several issues including flooding, Houses equipment to safely shut down all 3 units in the eventof catastrophic flood to Mode 3* Licensee constructed 5-ft walls around entrances to addressexternal flooding vulnerability.

, Licensees extended these walls to 7.5-ft in February 2009.OiNRCial Use Y -SeTY- 3Prolkif Ptople aa at h .rIm ,ommne Flooding* Licensee performed an ONS inundation studyin 1992-Required by Federal Energy Regulatory Commission (FERC) Emergency Action Plan(EAP) on Jocassee license to Duke Hydro-Only reproducible calculation on record., Inundation levels calculated ranged from 12.5to 16.8 feet, NRC service water inspection in 1994identified potential deficiency in the 5-ftentrance wall height to that of the inundation study.P Lv .r: y cl r Licensee Disposition Licensee argued that Jocassee Dam floods are outside oflicensing basis for ONS.Licensee committed to disposition of this deficiency as part oftheir IPEEE submittal in 1995, An assessment of the Jocassee Dam flood hazard was includedin the IPEEE without mention of the inspection issue., The staffs evaluation did not take issue with:-The derivation of the dam break frequency

-Other factors that the licensee used to reduce their riskestimates of external flood events-The lack of arguments to justify plant protection for floods inexcess of the eight of the protective walls at the SSF gradelevel.The licensee failed to note in the submittal or subsequent updates that there existed a recent inundation study that wasthe subject of an NRC inspection issue.SNficial s nly Secu -(;&UpS.NRC hddrInrnn NRC Staff Review of IPEEESubmittals

• Review of submittals for NRR was managed by RESe RES contracted national laboratories to conductreviewss Region II staff met with NRR staff on September 1,1994 which was documented in a memo-The Jocassee Dam rupture flood issue was discussed

-NRR staff stated that the external event hazardspreliminary review of Oconee would take several months-The memo stated that NRR staff considered the issue ofminimal importance without any bases for these views-In light of this, RES staff was not informed of this issue0 i Ue On6UjSI RCR rmto1CB~1T~WO NRC Staff Disposition of theOconee IPEEE Submittal o Given the submittal information, the staffs closeoutletter in 2000 stated-Duke's process is capable of identifying potential vulnerabilities associated with these issues at Oconee-Considered external event issues resolved.

• The closeout letter cites a dominant contributor toresidual risk involved Jocassee Dam failures andflood heights exceeding the 5-foot high SSF floodbarrier, thus rendering the SSF inoperable.

7 Re-emergence of Issue# The Reactor Oversight Program (ROP) identified aperformance deficiency against the licensee by theirmaking and keeping an opening in the side of theSSF below the 5-ft level for 2 years without anadequate evaluation.

e The flood height calculation resurfaced duringevaluation of the performance deficiency using theSignificance Determination Process (SDP) in 2006NRC staff reviewed the dam failure probability frequency and discovered a major flaw in thelicensee's calculation in 2007.jUSNRC 'ftici NPepk aud thef Empiometn r " ., : j -Actions Taken by NRC Staff# The NRC staff took the following actions to assess the Oconeefacility's ability to withstand severe flood events from apostulated Jocassee Dam break:-Initiated a design adequacy review-Developed an action plan-Staff assessed the design basis-Researched prior licensing actions related to flood protection s Reviewed other information to determine if the current plantdesign meets NRC regulatory expectations

, The staff used a collaborative, consensus-building approachamong 4 NRR Divisions and OGC to ensure appropriate regulatory practices were followed (e.g., backfit analysis).

, A draft backfit analysis was prepared(1U.SS RC 9noPIucdq Pe~ opte ard 11w Eior Results of Actions Taken by NRCStaff, NRC concluded that an adequate protection backfit exception may be the appropriate approach.

, Further determined that additional information from the licensee was required beforeadditional regulatory action is to be taken.-A 10 CFR 50.54(f) request for information letterwas sent to licensee on August 15, 2008.-Licensee responded to the letter on September 26, 2008-The NRC staff has reviewed licensee's responseletter to the 50.54(f) letter and is issuing a formalresponse.

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-, -1,, Yv. 0 I.- -Generic Implications s NRC staff has identified six (6) sites whichmay have a similar flood vulnerability s NRC staff planning on reviewing closeout ofGS1-156.1.2 s A proposed B.5.b review of possiblestrategies to mitigate core damages A generic communication via an Information Notice has been drafted and is in the processof concurrence.

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