ML14058A051

Slides on Oconee Nuclear Station - Standby Shutdown Facility (Ssf) Flood Barrier Breach Violation SDP Assessment

ML14058A051
Person / Time
Site:	Oconee
Issue date:	02/04/2014
From:	Office of Information Services
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References
FOIA/PA-2012-0325
Download: ML14058A051 (8)

Text

Oconee Nuclear Station Standby Shutdown Facility (SSF)

Flood Barrier Breach Violation SDP Assessment U.SNRC UUDSTAinSNICtLARREL~UTOiRY CONMISSMON ProtectingPeople md ate Envirnament

Nature of ViolationlPerformance Deficiency and SDP e Open penetration access cover inthe SSF exterior wall for approximately 2years.

eNo evaluation done by licensee.

- Licensee required to do 10CFR50.65(a)(4) or IOCFR50.59 assessment whenever a barrier isbreached as per RIS-2001-09, Control of Hazard Barriers.

1. Opening below 5-ft max. flood height identified by licensee in IPEEE.

', Susceptible to site flooding from rupture of Jocassee Dam 11-miles upriver.

• Licensee commissioned study from FERC concluded that floods can exceed 12-feet.

- Licensee claimed that FERC study was conservative.

- Despite that, licensee used the 5-ft height for IPEEE with a split fraction of 20% to account for floods exceeding that value.

(j.-)US.NRC UNITED STATES NULEAS RECLL&TOIAY COMMISSION Poetxsepeandthe Environwme

Nature of ViolationlPeuformance Deficiency and SDP Region IISRA performed analysis based on information from the licensee and apportioned flood height based on split fractions to arrive at a quantitative WHITE finding.

STATES UNIED M~jCILFA RlUTO1Y COMMISION ProtecdgPopl* nd the Environmnt

SDP Results Jocassee Dam Failure Mode Increase inCDF (per Reactor.Year)

+

Random 1.84 x10-6 Seismic 1.44 x1086 Total 3.28 x10s U.S.NRC RStIAM Ha~cumR"COMMMsIO1N Protec*in PeOPLe

the Envieonmet

Summary Timeline

. SERP meeting of August 17, 2006 assessed as preliminary WHITE with choice letter sent to licensee.

• Licensee waived regulatory conference.

• Final significance determination of WHITE sent to licensee on November 22, 2006 based on quantitative CDF and qualitative erosion of defense-in-depth.

s Licensee appealed the final significance determination on December 20, 2006 based on un-docketed and unreleased contractor information.

a Appeal panel convened on January 9,2007.

1. Licensee contractor seismic fragility analysis of Jocassee issued January 29,2007.

1. Appeal panel recommendations issued on February 22, 2007.

s Region IIoffice issued the final determination of WHITE on March 1,2007.

o Licensee issued further appeal on May 3,2007.

o Seismic fragility analysis was evaluated with follow up telecom to licensee on June 28, 2007.

1. Licensee response to analysis questions by email on July 17, 2007.

SU.S.NRC STATES IJNTED M.AEctARMMRY CONEIO' IhotectingPeople and theEnviron~ment

Jocassee Dam Random Failure

• Licensee computed random failure frequency based on operating industry history of failures for rockfill dams of over 50-ft inheight s Discrepancy exists on counting the denominator of total operating dam-years.

- Licensee lumped operating years of other dam types but, did not count their corresponding failures inthe numerator.

e Random frequency could be higher which might offset any uncertainty inthe resultant flood height difference between the bottom of the opening and the 5-ft height of the wall.

e Resultant ACDF could range from WHITE to RED in severity.

c.US.NRC UNITEDSTATESNUCLEARREGULATOY COMMON Protecting People and the £nzironment

Risk-informed Regulation and Defense inDepth a Used as away to account for uncertainties inequipment and human performance.

s The independence of barriers have been degraded.

s Licensee has an exclusive reliance upon the SSF to prevent core damage without redundancy or diversity of mitigation.

- Any functional degradation of the SSF flood barrier from these initiating events directly increased the failure probability of the SSF and therefore, increased the likelihood of core damage.

e Using a blended qualitative and quantitative perspective, the NRC's final Significance Determination remains low to moderate (White)".

SUS.NRC UNrTE STATE NCLURS!GtUTORY CO~M~M how~frng People and the Environment

Alternate Appeal Panel Evaluation

• Seismic fragility review did not endorse licensee's conclusions completely but felt that the frequencies were sufficiently "low". Therefore, only random dam failures were considered.

s Epistemic uncertainty inJocassee rupture frequency

- Licensee and NRC cannot resolve resultant flood height fractions resulting from below opening to 5-ft.

1. Assume that mean dam rupture frequency producing a 4.71-ft flood identical to a mean frequency producing a 5-ft flood.

s Using licensee's minimal IPEEE SSF failure cutsets results inACDF of 8.22 x10-6 per year.

~USSNRC ott*1hU a mRYCOMMISSION t nd heCI Protecting People and the Enzntoment