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 Calculations StephenCumblidge MaterialsEngineerNRR/DE/EPNB UnitedStatesNuclearRegulatoryCommission(U.S.NRC)
Tel:+13014152823 Email:stephen.cumblidge@nrc.gov Rockville,MD May212018
NRCUseofPFMCalculations TheNRChasbeenusingprobabilisticriskassessmentsto guideregulatorydecisionmakinginseveralareasfordecades TheNRChasusedtheprobabilisticfracturemechanics(PFM) codeFAVORtodevelopthealternatePressurizedThermal ShockRule(10CFR50.61a)
TheNRCiscooperativelydevelopingtheExtremelyLow ProbabilityofRupture(xLPR)Probabilisticfracturemechanics codetoevaluatetheleakbeforebreakmethodologyin systemswithactivePrimaryWaterStressCorrosionCracking TheNRCisopentoevaluatingandusingnewPFMcodesin thefuturetoassistinregulatorydecisionmaking,and recognizesthepowerfulinsightsprovidedbyPFM 2
BenefitsofPFMCalculations PFMCalculationscanprovide anoverviewoftheprobabilities ofcrackdepths,leaks,orfailure Onecandecideonaprobability ofaneventasopposedtothe binarycriteriaofa deterministiccalculation PFMandDeterministic Calculationscanbeeffective independentlyormaybe complementary
X or vs.
Deterministic PFM 3
ConfirmatoryCalculations WhentheNRCstaffperformsatechnicalreview,we checktheimportantcalculationsperformedinthe submittal TheNRChasexpertsinavarietyoffields,including PFM,toallowforthistypeofconfirmatorywork PFMcalculationspresentuniquedifficultiesfor performingconfirmatorycalculations 4
NovelPFMCodes Withoutaccesstothecodeorindependentreviewof thecodeitcanbeverychallengingtodetermineifthe PFMcalculationsareadequate 5
NRCReviewofaPFM Possiblemethodsforverifyingthecode
- HavingthecodedirectlyevaluatedbyNRCstaff (TopicalReport)
- Benchmarkingthecodeagainstacodewehavein house(xLPR,FAVOR)
- Benchmarkingthecodeagainstdeterministic calculations
- Independentpeerreviewbyabodywithno conflictofinterest 6
IssuesWithPreviousPFMCodes Unusualassumptions(e.g.extremelylow possibilityofacircumferentialflawinapiping weld)
PFMdidnotaccountfordegradation mechanismsseeninoperationalexperience Correctionfactorswithlittletonotechnical justification 7
PathForward TheNRCisdevelopingguidanceontheuseof PFMcalculationsinregulatorysubmittals Thisguidancewillhelptomakesubmittalsusing PFMcalculationsmorerobust,willallowfor moretimelyandpredictablereviews,andmake acceptanceofPFMsubmittalseasier 8