ML13159A009

Notable Failures in Nondustructive Testing - June 4, 2013 Public Meeting

ML13159A009
Person / Time
Site:	Davis Besse, North Anna, Diablo Canyon, Duane Arnold
Issue date:	06/04/2013
From:	Cumblidge S E Piping and NDE Branch
To:
Rezai A
References
Download: ML13159A009 (19)

Text

Notable Failures in Nondestructive Testing Stephen Cumblidge June 4 2013 GoalsofNDE Goals of NDE*Assurestructuralintegrityofcomponents Assure structural integrity of components*Assure leak tightness of reactor pressure boundary*Detect flaws before the y exceed acce p tance criteria yp*Detect and size flaws that meet acceptance criteria 2

WhenDoesNDEFail?

When Does NDE Fail?*Rationalizingawaydetecteddefects Rationalizing away detected defects*Use of NDE techniques that have not been properly qualified through Appendix VIII blind testing*Poor implementation of Appendix VIII-qualified NDE procedures*When Appendix VIII-qualified procedures miss flaws*When NDE is not Used 3

Rtiliidttddft R a ti ona li z i ng away d e t ec t e d d e f ec t s 4 2000 Davis Besse HdLk H ea d L ea k age*NDE failures can happen even when the detection is clearAthi*A ny t ec h n ique can fail if assumptions

are incorrect 5

DavisBesse2010 Davis Besse 2010*The replacement pressure vessel head leaked in 2010

• Withincreasedsurveillanceandabetterunderstanding With increased surveillance and a better understanding the degradation was caught quickly *NDE was used in identifying where the cracking was located 6 UfNDEthithth U se o f NDE t ec h n i ques th a t h ave not been properly qualified 7

North Anna Steam Generator 2012 2012*In March of 2012 at least five ilflidb ax i a l fl aws were m i sse d b y an ultrasonic inspection*The licensee used a site specificmockuptoqualifythe specific mockup to qualify the inspection procedure as PDI has no matching test blocks*The licensee used an encoded phased array technique to search for circumferential flaws*The licensee used an lifidllti unqua lifi e d manua l u lt rason i c search unit to search for axial

flaws 8 FactorsinNorthAnna2 Factors in North Anna 2 *The North Anna 2 root cause analysis dibdidttiid The average POD requiredTo miss five flaws is 13%d escr ib e d i na d equa t e t ra i n i ng an d oversight*Team scanning was used

• Thesearchunitshadnotbeenqualified

• The search units had not been qualified via the blind Appendix VIII process-The ultrasonic search units were more than ten degrees off of the specified angle-The ultrasonic search units were unable to get a strong signal off the end of the site specific mockup block

-Modelingshowsthatthesearchunitswere Modeling shows that the search units were not optimized for the component*The probes looked nearly identical but were "Sided", meaning that if the wrong probewasusedtheinspectionquality probe was used the inspection quality would be severely degraded 9

Pilttiflifidthi P oor i mp l emen t a ti on o f qua lifi e d t ec h n i ques 10 DuaneArnold2007 Duane Arnold 2007*Two recirculation riser nozzle-to-safe end dissimilar metal welds at Duane Arnold, RRC-F002 and RRF-F002, contained surface-breaking cracksEidhthtthkt

• E v id ence s h ows th a t th e crac ks were presen t as early as 1999

• Inspectionsconductedin1999and2005failedto Inspections conducted in 1999 and 2005 failed to detect the cracks*The cracks were found during an inspection in 2007 didt6ihld74%thhll an d s i ze d a t 6 i nc h es l ong an d 74% th roug h wa ll in RRC-F002 and 6 inches long and 55% through wall in RRF-F002 11 MissedFlawsatDuaneArnold Missed Flaws at Duane Arnold*The 1999 ins p ection procedure was not A ppendix VIII ppppqualified and the weld crown reduced inspection coverageEvidencefortheflawswaspresentbutnocallwasmade

-Evidence for the flaws was present but no call was made*In the 2005 inspection the weld crowns were removed and an Appendix VIII qualified procedure was used*The 2005 inspection unfortunately used an inappropriate couplant and yielded a low-quality scan Theprocedurewascapableofdetectingtheflaw

-The procedure was capable of detecting the flaw-The inspectors should have rescanned to obtained better coverage-Low quality evidence for the flaw was present but no call was

made 12 Poor Coverage -Weld Crown In Place 1999Weld RRF-F002 6"CircumferentialCrack 6 Circumferential Crack55% Through WallNoWeldCrownbutPoorNDE2005No Weld Crown Good UT Procedure 2007 No Weld Crown but Poor NDE 2005 13 WhenAppendixVIIIQualified When Appendix VIII Qualified Procedures Miss Flaws 14 DiabloCanyon2013 Diablo Canyon 2013*Diablo Can y on had allo y 52 weld overla y s installed in a yyy several pressurizer welds in 2008*An acceptance examination was performed using an AdiVIIIlifidtillltd A ppen di x VIII qua lifi e d conven ti ona l manua l u lt rasoun d procedure, including a zero degree inspection to find

fabrication flaws*An examination in 2013 using manual phased array UT found several laminar flaws missed by the acceptance examination examination*One of the flaws was 16 inches long and a second was essentiall y 360 de grees around the overla yygy 15 DiabloCanyon2013 Diablo Canyon 2013*Both the 2008 and 2013 techniques wereAppendixVIIIqualified were Appendix VIII qualified*The zero degree beam inspection procedure used for the acceptance examination did provide small responsesfromtheflawsbuttheflaws responses from the flaws but the flaws were not all found were not sized

correctly in 2008*The procedure used in 2013 used a manualphasedarrayprobethatZero DegreePhased Array manual phased array probe that included many more angles than were used in the acceptance examination*The laminar flaws were at a slight angleanddidnotpeakatzero angle and did not peak at zero degrees*The NRC met with PDI to discuss the Mockups used at PDI and the path forward forward 16 WhNDEiNtUd Wh en NDE i s N o t U se d 17 Leaks in Uninspected Ct C omponen t s*Man y com p onents prone to leakin g are not yppgvolumetrically inspected-Partial Penetration WeldsPressurizerHeaterSleeves

-Pressurizer Heater Sleeves-Socket Welds-Small Diameter Welds*If the goal of NDE is to prevent leakage these areas would need to be addressed with more aggressive NDE 18 Conclusions Conclusions*No ins p ection procedure can succeed if the ins p ectors pppand/or the licensees rationalize away detected indications

• WhenAppendixVIIIqualifiedproceduresareused When Appendix VIII qualified procedures are used appropriately, ultrasonic inspections have shown to have a high reliability

• Thereliabilityofinspectionproceduresdeclinessharply

• The reliability of inspection procedures declines sharply when the procedures deviate from the Appendix VIII-

qualified proceduresEAdiVIIIlifiddifl

• E ven A ppen di x VIII qua lifi e d proce dures can m i ss fl aws*If the NRC and industry goal is to prevent leakage NDE will need to be im plemented in new areas p 19