ML14058A028
| ML14058A028 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/21/2008 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML14055A421 | List:
|
| References | |
| FOIA/PA-2012-0325 | |
| Download: ML14058A028 (11) | |
Text
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O~~ffcil,
ý$e nly - Sensiti/ve j**-S.NRC0--ntrnt Oconee Flood Protection and the 10 CFR 50.54() Response NRR LT Meeting October 21, 2008 October 21, 2008 1
U.NRC Interna Pm,I
\\CU*11 LAl COM Objectives Purpose
-Summarize the licensee's responses
-Discuss the staff's evaluation and options
-Discuss possible paths forward
-To receive LT feedback on the merits of possible paths forward October 21, 2008 2
t L*I't IIInItera II S
rmt" PmS.li nR
Background
Duke Hydro/FERO Inundation Study completed in early 1990s. Estimated flood heights up to 16.8 ft above SSF grade level
- First identified by inspectors in 1994.
- Floods in excess of 5 ft lead to three-unit core damage event.
, Staff identified an under-estimate in licensee's random dam failure frequency for Jocassee.
, Staff discovery that the Jocassee dam failure issue had not been adequately resolved.
, Issued 10 CFR 50.54(f) letter for Duke to address flooding concerns.
October 21, 2008 3
.NARC Principal 10 CFR 50.54(f Questions Regarding Oconee Flood
- 1. Explain the bounding external flood hazard at Oconee and the basis for excluding consideration of other external flood hazards, such as those described in the Inundation Study, as the bounding case.
- 2. Provide your assessment of the Inundation Study and why it does or does not represent the expected flood height following a Jocassee Dam failure.
- 3. Describe in detail the nuclear safety implications of floods that render unavailable the SSF and associated support equipment with a concurrent loss of all Alternating Current power.
October 21, 2008 4
\\Unhcia us e Iy-ens ive
-US,NRC I
.,jnrnal I n
Prokix; Propk aidt du Emnment 50.54(f Letter Review Team Scope
- Review submittal as if NRC is reconstituting a design basis flood for Oconee
- All modes/events causing external flooding will be assessed
- All modes/events causing Jocassee dam failure will be assessed s Topics considered in development of.options:
- Likelihood of dam failure
- Flood analysis
- Seismology
- Basis for continued operation
- Security October 21, 2008 5
- 4OfOf, se Only - SeniTlive
- U.S.NRC
\\
fotio_
NiedinghPopk.diEivrome, Overall Summary of Licensee's Response
, Inundation levels based on current drought conditions
-Supports continued operation
, Commitment to increase current flood walls to 7.5 feet by February 2009.
- Further analysis by February 2010.
, Heavy reliance on test and inspection of dam
, Seismic failure is "not credible" Other dam failure modes (i.e., overtopping) "not credible" October 21, 2008 6
IKUS.NRC u yeUHoov frTLULAI UTUR COWW.u cvI Overall Summary of Staff's Review of Licensee's
Response
Interim continued operation appears feasible with additional licensee commitment of water management Licensee failed to fully address site flood height (e.g,,
adequate protection)
- No analysis for random Jocassee Dam failure at full pond level
- An inadequate seismic analysis
- Did not perform a Probable Maximum Precipitation (PMP) analysis
, Future planned analysis for dam failure is not acceptable
- Issues on time-to-failure, breach size, and choice of flood model
, Current and future reliance on probability arguments is not acceptable October 21, 2008 7
U.
S.NRC
'~K~nIIrt.j9 2 Izulicq Peapk ad t6 EuwoanmaOptions for Path Forward
, Options represent choice between engineered and analytical approaches
- An engineered solution Installation of watertight doors to the SSF Has not been committed to by licensee
- An analytical approach Analysis was proposed by the licensee October 21, 2008 8
\\ý I'dMUDITUDS UM [Li.IL*l ARIM CNMMlI.%*
h'°*a ped&Summary of Option 1 Engineered Solution (Installation of watertight doors)
Pros Cons
- Independent of all sources of flood and inundation level
- Fully addresses adequate protection
- Fewer NRC staff resources required for inspections and review Timely and defensible to internal and external stakeholders Licensee might delay acceptance of this solution October 21, 2008 9
- )UOSNRC Pros Summary o Option 2 Further Analytical Solution Cons s Improved estimate of flood inundation level to define amount of protection to be applied s Licensee-proposed solution
, A resolution timeframe may be prohibitive
- Licensee has inappropriately eliminated failure modes High degree of uncertainty in dam breach analysis Analysis plan for Feb. 2010 is not adequate
- Calculated inundation level may result in a further engineered solution
° Probability approach is not acceptable
, Requires very extensive staff review resources October 21, 2008 ONfli e Iy -S sV, Internal In rm ionn 10
USNRC Pming PekpI and W Ui~ rownmt Outline of Presentation to Licensee on October 30, 2008 Management Meeting
, State basis for interim continued operation
. State NRC position on dam failure frequency (probability) argument
- NRC will not expend staff resources on an approach which will not contribute to a solution
- Licensee's proposed probability approach of eliminating failure modes with inappropriate bases is not acceptable to NRC staff
- State NRC position on preferred option
, State regulatory vehicle to pursue
- An order
- A Confirmatory Action Letter October 21, 2008 11