ML13052A783
| ML13052A783 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 02/06/2013 |
| From: | Office of Information Services |
| To: | |
| References | |
| FOIA/PA-2012-0325 | |
| Download: ML13052A783 (12) | |
Text
"OFFICIA UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, DC 20555-0001 NRC INFORMATION NOTICE 2-04G201 1-xx:
APPLICABILITY OF HISTORICAL DAM FAILURE FREQUENCY EST]MA-TE-SU N D ERESTI MATED IN PROBABILISTIC RISK ASSESSMENTS ADDRESSEES All holders of an-operating liconse or construction pormitlicensees for a-nuclear power FeaatG efP-rAductin-and Utilization Fai tties,"reactors except those who have permanently ceased Fratted: No widow/orphan control operations and have certified that fuel has been permanently removed from the reactor vessel.
All holders Of or applicants for an early site per.it, standard design "ertific-a*iie standard 41icenses. Certifi.cAtionRs, -and-Ac0roValS for NuGlcar Power Planrts)'"
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iF3ei PURPOSE The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert addressees of a potentially non-conservative value for dam failure frequency estmate-used.in exernalleeoodirg-4afynsa-that originated in 1980s reference documents ptu
-qshe,44he4-98*
and was commonly adopted by someelicensees in their probabilistic risk assessment (PRA.):-
for external events. Using a non-conservative dam failure frequency may result in underestimating the risks to the plant associated with external flooding or loss of heat sink from the failure of upstream and/eo downstream dams or levees. It is expected that recipients will review the information for applicability to their facilities and consider actions, as appropriate, to correct any error resulting from the-use-of-these reference documents. However, suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.
DE wRITISnh OF GIRGUMS1.CE BACKGROUND The NRC staff recently reviewed the useof-Lidentified a potentially n on-conservative value for dam failure frequency estioatesr peviously publishcd in dcumnetrt-&related4-o-P RA-fm nuclear power plants. Analysis performed in a PRA study (NSAA98Iýbycontained in the ML090510269 GFFie-rA1-USE-GNLY--i..CEL
ýr2REATED INF9RM*TIOI-.
- FICAI"E N
I SCU[JRITY-RELATFID INF' lIO.
IN 2011-XX Page 2 of 4 Nuclear Safety Analysis Center (NSAC) of the Elect utilities has boen usod by licensees performing ede Fri Pewfr Institute (EPRI) ad participating Fna f!Gcdinu unuI"v'e-t-' evalwantr k
NRC on external event con-tributors to overall risk for the U.S.
'nt-report published by the US nuclear power plants, titled "NUJREG!R 0.. 2, Evaluati.n of External Hasardd to Nuclear Power Planrt in the nRited States" also refers to the NSAC/60 study 9R the subject, "Oconee PRA a Probabilistic Risk Assessment of Oconee Unit 3." This dam failure frequency estimates (e&USNRC-1.987),
value was commonly adopted by licensees in their PRA for external events. Published in 1984, NSAC/60 provided an estimate for a dam was prepared by NSAC in coniunction with Duke Power Company and provided their calculated value for the dam failure frequency of the Jocassee dam, a value commonly referenced by other licensees in their flooding analyses. The a*alysi6. The framework used in NSA,. 60 to develop this e6timate.as the c
,mpilation G
hasteFialfor the Jocassee dam failure ev.nts and oeperational years doom..ed applicable tO specific dam characteistic s eonsidereedn i the study (a lafge, mordern embankmentsdam),
nformation a;;vilable when the study was published by,i) dam ffcon4pe
-(4ii)-eenstFUtiG c.pletin; date, and (iii) failure m.des.
Aby compiling data for similar types of dam failures, while taking into account a mathematical equation modeling that showed that more recently constructed dams displayed a decrease in generic damlower failure rates with an increase in Gperat e
-a-dam-years-wa.&-assumeedfrequency, presumably due to refleGt-improvements to metheds Efin dam design and construction.-A NSAC/60 states that a Bayesian analysis using historical dam failures was then-performed to estimate the annual failure frequency at the time the analysis was performed (1981) and associated uncertainty range for dams built within different time periods: 1900- 1981, 1940- 1981, and 1960- 1981. The NSAC/60 PRA analysis determined the median annual failure frequencies in-NSACG69-are4nfor the range betwee-e
!.0Jocassee dam as 2.3 x 10-5/year-apAd-2,-5 1.6 x 10 5/year-_ and 1.4 x 10"5/year, respectively, from causes other than earthquakes and overtopping (which NSAC/60 states were considered in separate analyses.)
This study.. c...izedThe NSACI60 approach estimated the failure frequency for the Jocassee dam by screening the available historical data for U.S. dams at the time of the analysis (1981) and using only the data deemed applicable to the Jocassee dam based on characteristics such as (i) dam composition, (ii) construction completion date. and (iii) failure modes. NSAC/60 describes the challenge in collecting sufficient historical information based on the scarcity of the data applicable to the specific dam characteristics considered, as well as the complexity of the actual phenomena controlling dam failures and its potential impacts to a nuclear power plant site...
.bsequ.e..tly, The NRC subsequently included the NSAC/60 dam failure frequency results in NUREG/CR -042, "Evaluation of External Hazards to Nuclear Power Plant in the United States" (Agencywide Documents Access and Management System (ADAMS) Accession No. ML062260222), which was initially published in 1987. NUREG/CR-5042 reported bounding calculations with results of "10 6/year or even smaller" for modern well-engineered dams and a FiiAL USE,,,,,..Y - SEURITY-RELATED iNFORMfAT;N--
IN 2011-XX Page 3 of 4 range of values between "104/year and 105/year," referring to NSAC/60 in both cases4U&N-R-G-.
DESCRIPTIO OF CIRCUMVSTANES BACKGROLNO Relatcd NRC Comm'-nications U, S. N uGlor Reg u latoy G ommi~s~i on, 'Eyaluation of EXterna! HazarFds to Nucl~ear Rowe Plants4RnAhe--Lited-States--N-UREGI-CR-5042..-L-awrenoe--.iverGmrerational Laboratory, Doccmber 1087, ADAMS Acsin Pio, ML0622-60222-Stan#Fod iV.r..y, DepaftmeR-t
.f C.vil.and ERViFrom..
a-e +neent.ala Pformans, of Dams Program (htto+÷!. do s
,a,
r
.ed
., x US Army Corps of Enginccrs, National Invontory of Dams (httU!!.id sag.a.;,
,mO)
Relate d non NRC CcFmmun;catioems
"- N""G'"a Safety Analysis Center4E!ectriG DPe"eF-*......
h IR'÷*÷"÷ "NSAG-6,C 4s PRA4:= A Probabilistic Risk Assessment Of OGoneo Unit 3," Palo Alto, CA, 19847 Bacoher, G, B., M. E. Pat6, and R. De Neu~'ille (1980), "Risk of Dam Failure in Bcnofi GGst-A44alysis,"
atr-Reosc.
R-sears 1
-449-456-
_Martz, H.F., and MC. Bryson (1082), "Predicting Low ProbabilityHigh
.ons..uo...
Events,.Proceedings. of the Workshop-or-Low-Probability/High-Gonsequence Risk Analysis, Juno 15 17, 1082, Arlington, Virginia FoE.ster M, Feil R, Spannaglc M (2000a), "The statistics of embankment dam failures a*d aGcidents," Canadian Goet"÷h"i"a! journal, 37, 1000 1024.
f---l-eseM-Pe R-pR-e M0 dams-bypiping0b-)-a-mnadianeeGe6 hnsatr-a
-,25 0.iketheod-of Do yR./(0 sty" ACRES lntcrnat Hnvations Autumn EhErtieo
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....... Extreme-Floods f.- Dam*
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IN 201 1-XX Page 4 of 4 Safet Risk As.es.emnt," U.S. Departmcnt of the lnRtercr, T-echRicl Sep,ýie Goentr, Denver, CO, 1909.
-U.S.
Bureau of Reclamation, "Dam Safety Risk Analysis Methodology," Version 3.3.1, U.S. DepartMent of the-#te~ior, Tehni.call S C....ent*r, Denver, CO. 2003.
-U.S. B-ur-eau Gf Reclamation, 'Dam Safety Risk Analysis Best Practice6 Training Manual," Version 2.0, U.S. Department of the interior, Technical SerF'ico Ccnter, Denver, CG0, 2040, DISCUSSION While revisiting this estimate, thc NRC staff recently reviewed the use of dam failure frequency estimates in NSAC/60. The NRC staff noted that many assumptions in the dam failure rate estimation approach used in NSAC/60 are strongly dependent upon the completeness and accuracy of the dam data used and the criteria for including or excluding certain failure events and operational years deemed to be applicable to characteristics specific to the dam considered in NSAC/60 (i.e., type, height, construction year, and years of operation)._ In particular, the failure frequency derived in NSAC/60 was considered to be representative of failure modes resulting from causes other than hydrologic (e.g., severe precipitation), and seismic events-,
which NSAC/60 states were considered in separate analyses. In effect, this choice of exclusions eliminates the majority of failure modes that has been historically observed for dams (e.g., overtopping)._ Additionally, the phenomena associated with non-hydrologic, non-seismic (e.g., internal erosion/degradation) events was further screened for other failures modes not deemed applicable based on design considerations also specific to the dam censidered in the studyJocassee dam (i.e., piping through a conduit passing through the dam, and structural failures of the spillway during flood discharge).
To assess the impact of thesethe NSAC/60 screening assumptions, the NRC staff reviewed currently available US-databases for beth-U.S. dams. In order to determine generic dam failure frequencies, the databases are used find (i) the number of historical failures of dams of a particular characteristic such as dam type and (ii) the total number of years of operation of dams of the same characteristic. The NRC staff reviewed databases of historical dam failure events-(,
primarily7 the National Performance of Dams Program by Stanford University4-apn64e-,
http://nodo.stanford.edu/index.html, and the database of the existing population of U-SU.S. dams k-the National Inventory of Dams maintained by the J4USU.S. Army Corps of Engineers) that plevide (USAEC), http://nid.usace.army.mil). [While USACE Web site states "Non-government users are no longer able to directly download any data from this site." non-government users can request access to the data by contacting the USACE staff member specified on this Web site.] While these databases contain valuable historical information and are certainly more complete and accurate than information than available when NSAC/60 was prepared.Whtle valublehisoricl iforAto i~s;cntinod in both datab@,ases the NRC staff -lso obs-eRd the NRC staff found inherent challenges in using the databases for PRA purposes that limit the ability to soundly iustify a very low value of dam failure frequency using only historical data. The databases were not created for the specific purpose of performing dam PRAs and were not desiqned to be used together. As such, the NRC staff found that data was not always complete,
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1FFIIA.L6 ueNLV-SECUORITY-RE LATE D-INF-ORM ATION-IN 201 1-XX Page 5 of 4 consistent, and sufficiently detailed for use in PRAs. For instance. NRC staff found that for PRA purposes there was an inherent challenge regarding the incompleteness of failure event accounts (e.g., construction year of failed dam, and failure mode), sparse data and inconsistencies on definitions used on both failed and operating dams (e.g., dam types).
In d,,it.iTo understand the impact these inherent databases challenges, the NRC staff asce performed analyses of the ranges of generic dam failure frequency estimates that can be derived from these databases-as-wel -a -aa. The NRC staff also reviewed literature review-on previously published dam failure rates. -The NRC staff also reviewed literature review included on published analysesdam PRAs mostly based on historical evidence for the USU.S. and the international population of dams: Bechor et a! (1
- .-MartzandBso-(-982)iOL--(499 Poster et a! (2000a); Foster ef a! (2000b); Donnelly (2004); and US8R (201 0). From both offorts,ý the-. The NRC staff also reviewed available information e
vides-significait evideRieon the latest dam risk assessment methodologies including the following publications from the U.S. Department of Interior's Bureau of Reclamation at http://www.usbr.gov/library/: "A Framework for Characterizing Extreme Floods for Dam Safety Risk Assessment," issued 1999:
"Dam Safety Risk Analysis Methodology," Version 3.3.1, issued 2003; and, "Dam Safety Risk Analysis Best Practices Training Manual," Version 2.0, issued 2010.
Based on this review. the NRC staff determined that generic dam failure freqiieciesfreguency estimates that are considerably lower than 104/year may not be justifiable based only.on historical dam performance information. Additionally, as stated in NWUR=,!,R
- 0*2, dam failure ratee-above--thies-al ue. are..als 9 pessibe..arnd-, therefofeý.-a tehnical.I.just64ication.weuid-have-lo-be PFrvided in support cf any specific estimate usd. This is due to the variability on site-specific characteristics (i.e., hydrologic, geologic, and operational) and the potential contributions of site-specific failure modes not covered by databases, such as the potential activation of failure modes in dams which have never been filled beyond a certain operational reservoir level (e.g.,
first-fill scenarios). This is compounded by the data analysis challenges discussed above.-In reg-thi-s-oenei in-,tAhe-N R-G-staff-alsc-Gensidered-.available-nfeoraten-n-urent.-state-of art mnetheedlogie in rFik aSSeSSm.ent Of damns published by mrultiple sources, including federal-agene-eh-as-he4S-Detrnent-ef-Iae4e*Bureu.ef.Reeamaten.(e*.U&
19990 ISBR, 2003).
In concluseonDISCUSSION Both NSAC/60 and NUREG/CR-5042 are commonly used primary reference documents for licensees performing external flooding analyses incorporating a dam failure and applied to any type of dam. However, recent NRC reviews determined that the generic failure frequency estimate used in NSAC/60 combined generic information with site-specific screening criteria that produced median values an order of magnitude lower than published literature and NRC staffs assessments support._ Consideration of data sources currently available also indicates that (i) such significantly lower values may not be justified by historical data alone, and (ii) applicability of the NSAC/60 estimate to other dams with different characteristics may be inappropriate.
Reasons for these conusionethis include the fact that generic failure frequency values may not account for site-specific features and can be highly dependent on completeness and applicability of available information to site-specific dams; which may counteract conservative QEEDJA6VSEVNtV --S-EC-U-R-IT-Y--R-E-L-A7-E-MNFC)RMA-TION,
OFFICIL USEfL*
NPORMAO IN 2011-XX Page 6 of 4 assumptions in the use of data.
These considerations recognize that data available in these databases is useful in derivinq bounding values and approximate generic dam failure rate estimates, but that the justification for its use in obtaining significantly lower values than the established averages may not be conservative may result in inappropriate estimates of the risk of external flooding or loss of ultimate heat sink, depending upon how such dam failure frequencies were used, Although there is no specific regulatory requirement to do so, licensees may use this readily available dam data to develop a facility-specific dam data set in order to update the dam failure frequency value specified in their PRA for external events.
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a between Latin and Asian text, Don't adjust space between Asian text and numbers questions about this matter to the technical contacts listed below, spacebtenAin text andn Timothy J. McGinty, Director Division of Policy and Rulemaking Office of Nuclear Reactor Regulation Technical Contacts:
Fernando Ferrante, NRR/DRA 301-415-8385 E-mail: fxf3(,nrcgov Jeffrey Mitman, NRR/DRA E-mail: itm1(Znrc.qov Note' NRC generic communications may be found on the NRC public Web site httfn://www nrcg ov tinder Electronic ReAdinA Rnnm/Dnc.ijme.nt Collepctinn.n OPFMTXC'Dgff -CWLY --S-E-CURrT-f-WE-LATED-INFORMATIO.N-
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,,ing purpcses.mav result in inappropriate estimates of the risk of external flooding or loss of ultimate heat sink, depending upon how such dam failure frequencies were used. Although there is no specific regulatory requirement to do so. licensees may use this readily available dam data to develop a facility-specific dam data set in order to update the dam failure frequency value specified in their PRA for external events....
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f IN21021-xx Page 64 of 54 CONTACT This information notice requires no specific action or written response. Please direct any questions about this matter to the technical eeGta tcontacts listed below.
XXXXXXXXXXXTimothy J. McGinty, Director Division of Policy and Rulemaking
-Office of Nuclear Reactor Regulation Technical Contacts: - Fernando Ferrante, NRR/DRA 301-415-8385 E-mail:_xf3@rnrc.gov -.-.--------------------------
Jeffrey Mitman, NRRIDRA 301-415-2843 E-mail:_jtm..@pnrco.gqy Note: NRC generic communications may be found on the NRC public Web site, Ih ttp./w w. nrc.gv,. un~der Electronic Reading _Room/Document Collections............................
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