ML18141A393
| ML18141A393 | |
| Person / Time | |
|---|---|
| Issue date: | 05/21/2018 |
| From: | Stephen Cumblidge Piping and NDE Branch |
| To: | |
| Rezai A, NRR-DMLR 415-1328 | |
| References | |
| Download: ML18141A393 (8) | |
Text
NRR Perspectives on Probabilistic Fracture Mechanics CalculationsStephenCumblidgeMaterialsEngineerNRR/DE/EPNBUnitedStatesNuclearRegulatoryCommission(U.S.NRC)Tel:+1 301 415 2823 Email:stephen.cumblidge@nrc.govRockville,MDMay212018 NRCUseofPFMCalculations TheNRChasbeenusingprobabilisticriskassessmentstoguideregulatorydecisionmakinginseveralareasfordecades TheNRChasusedtheprobabilisticfracturemechanics(PFM)codeFAVORtodevelopthealternatePressurizedThermalShockRule(10CFR50.61a)
TheNRCiscooperativelydevelopingthe"ExtremelyLowProbabilityofRupture"(xLPR)ProbabilisticfracturemechanicscodetoevaluatetheleakbeforebreakmethodologyinsystemswithactivePrimaryWaterStressCorrosionCracking TheNRCisopentoevaluatingandusingnewPFMcodesinthefuturetoassistinregulatorydecisionmaking,andrecognizesthepowerfulinsightsprovidedbyPFM 2 BenefitsofPFMCalculations PFMCalculationscanprovideanoverviewoftheprobabilitiesofcrackdepths,leaks,orfailure OnecandecideonaprobabilityofaneventasopposedtothebinarycriteriaofadeterministiccalculationPFMandDeterministicCalculationscanbeeffectiveindependentlyormaybecomplementary X or vs.Deterministic PFM 3 ConfirmatoryCalculations WhentheNRCstaffperformsatechnicalreview,wechecktheimportantcalculationsperformedinthesubmittal TheNRChasexpertsinavarietyoffields,includingPFM,toallowforthistypeofconfirmatorywork PFMcalculationspresentuniquedifficultiesforperformingconfirmatorycalculations 4
NovelPFMCodes WithoutaccesstothecodeorindependentreviewofthecodeitcanbeverychallengingtodetermineifthePFMcalculationsareadequate 5 NRCReviewofaPFMPossiblemethodsforverifyingthecode-HavingthecodedirectlyevaluatedbyNRCstaff(TopicalReport)-Benchmarkingthecodeagainstacodewehavein house(xLPR,FAVOR)-Benchmarkingthecodeagainstdeterministiccalculations
-Independentpeerreviewbyabodywithnoconflictofinterest 6 IssuesWithPreviousPFMCodes Unusualassumptions(e.g.extremelylowpossibilityofacircumferentialflawinapipingweld)PFMdidnotaccountfordegradationmechanismsseeninoperationalexperienceCorrectionfactorswithlittletonotechnicaljustification 7
PathForward TheNRCisdevelopingguidanceontheuseofPFMcalculationsinregulatorysubmittals ThisguidancewillhelptomakesubmittalsusingPFMcalculationsmorerobust,willallowformoretimelyandpredictablereviews,andmakeacceptanceofPFMsubmittalseasier 8