ML18012A715
| ML18012A715 | |
| Person / Time | |
|---|---|
| Issue date: | 01/16/2018 |
| From: | Stephen Cumblidge NRC/NRR/DMLR/MPHB |
| To: | |
| Rezai A, NRR-DMLR 415-1328 | |
| Shared Package | |
| ML18002A510 | List: |
| References | |
| Download: ML18012A715 (20) | |
Text
CoverageBasedReliefRequests StephenCumblidge NRC/IndustryNDETechnical InformationExchangeMeeting January1618,2018
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Background===
10CFR50.55a(g)(5)(iii)was originallyintendedtobeused whenASMECodechangesina waythatbringsaplantoutof compliance Theimpracticalityrulewasnot intendedtobeamultidecade solutiontobeapplied repeatedlytothesame components Licenseessubmitrepetitive reliefrequeststotheNRC, consuminglicenseeandNRC resources 2
Plants Plants ASMECode Plants Plants ASMECode Plants Plants ASMECode OriginalIntent Reality Plants Plants ASMECode
Whyover40years?
- WhileNDEtechnologyhasimproved,manycomponent geometriesandmaterialsremainchallenging
- Formanywelds,theobtainingcodecoveragewould requiretheredesignandmodificationofthe component
- TheNRCstaffdoesnotsupportremovingcomponents withgoodOEfromexistingplantsoveracompliance issue
- ThereliefrequestprocesshasworkedwellandtheNRC didnothaveamotivationtomandateachange 3
TechnicalBasisforReducedCoverageRelief Requests
- Farsideexaminationsarenotabletodetect smallflawsreliably,butareexpectedtobe abletodetectlargeflaws
- Operationalexperiencewithreduced coverageinspectionshasbeenfavorablein recentdecades
- Asignificantamountofengineering judgementisused 4
SomeNotableExceptions
- TherehavebeeninstanceswheretheNRChas grantedrelieffollowedbyflawsbeingfoundin acomponent
- Atleastoneleakhasoccurredafterrelief
- Nopipefailureshaveoccurredinapipe coveredinanimpracticalreliefrequest 5
NotAllCoverageisCreatedEqual
- Somemethodsworkbetterthanothers throughaweld
- Manualphasedarraylikelyoutperforms conventional
- Encodedinspectionshaveadvantagesover nonencoded
- Difficulttoquantifythedifferences 6
CurrentStatus
- Thecurrentprocessprovidesreasonable assuranceofstructuralintegrityandleak tightness
- Thecurrentprocessislargelybasedon operationalexperienceandengineering judgment
- Changestothecurrentprocesswillrequirea clearunderstandingastowhythecurrent processhasbeenworkingwell 7
NRCResearch
- WhiletheNRCand Industryhavebeen dealingwithrelief requestsfordecades, noefforthadbeen madetoquantifythe causesoftherelief requests
- Researchwas conductedintothe maincausesofmissed coverage 8
GoalsofNRCResearch
- Determinethemaincausesofmissed coverage
- Determinetheflawsthatcanbedetected whencoverageislimited
- Austenitic
- Ferritic
- CASS
- UseofModelling 9
CausesofMissedCoverage
- Themajorityof missedcoverage examinationsare causedbysingle sided examinations 71%
29%
Single Double 10
CausesofSingleSidedExaminations
- Themostcommon causeofsingle sided examinationsare pipetovalve configurations 42%
14%
13%
9%
6%
16%
Valve Tee Nozzle Elbow WeldOLet Other 11
FarSideExamination Howmuchofaflawhastobeinabeam beforeitcanbereliablydetected?
?
Ferritic?
Wrought?
CASS?
Conventional?
PhasedArray?
Encoded?
12
NoCornerTrap Howmuchofaflawhastobeinabeam beforeitcanbereliablydetected?
No
?
Hopefully Ferritic?
Wrought?
CASS?
Conventional?
PhasedArray?
Encoded?
13
UltrasonicModeling
- Modelingmaybeusefulindeterminingthe effectivenessofanexamination
- TheNRCwillhaveconfidenceintheuseof modelingwhenenoughexperimentshave beenconductedandtherelationshipbetween UTmodelingandexperimentshasbeen established 14
ReducingImpracticalReliefRequests
- Newtechnologycanallowforcomplete coverage
- Codecoveragerequirementscanbechanged withasufficienttechnicalbasis
- TheNRCcanchangetherulesforhowreliefs aregiven 15
NewTechnology
- Whilethisistheidealsolution,itis challengingtomandate
- Evenifthenewtechnologyemerges tomorrow,itwouldtakemanyyearstoreach thefield 16
ChangestoASMECode
- N7111willlikelyeliminate70%ofpiping reliefrequests
- Theremaining30%willbecomplexcasesthat mayrequireNRCreview
- TheNRCwilladdressotherpossiblechanges astheyarise 17
CodeCaseN7111
- N7111redefinesthe requiredinspectionvolume insomecases
- N7111ismosteffectiveat reducingreliefrequestsfor singlesidedexaminations
- N7111islessusefulfor othertypesofobstructions, suchaspartialobstructions oftheentireweldwidth 18
X
Changesto10CFR50.55a
- TheNRCstaffhavebeenexploringpossible changestohowimpracticalreliefrequests, especiallyrepetitivereliefrequests,are handled
- Onechallengeistocraftrulesthathandlenew reactors,existingreactors,andnovelreactor designs 19
PathForward
- TheNRCstaffisconductingresearchinto determiningtheeffectivenessofexaminations withmissedcoverage
- TheNRCstaffvotedforN7111attheASME Codestandardscommittee
- TheNRCstaffislookingintorulemakingor policychanges 20