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{{#Wiki_filter:M arch 15 , 20 07 CA L N o. N RR-07-0 03 M r. Jo hn S. Ke ena n Se ni or V ic e P resi den t an d C hi ef Nuc le ar Off ic e Pa ci f ic Gas and E le ctri c C ompa ny Di abl o C any on Po w er P la nt P.O. B ox 77 000 0, M ai l Co de B3 2 Sa n F ranc is co, CA 94 177-000 1 S U B JE C T:
{{#Wiki_filter:March 15, 2007 CAL No. NRR-07-003 Mr. John S. Keenan Senior Vice President and Chief Nuclear Office Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 770000, Mail Code B32 San Francisco, CA 94177-0001
C ON F IR M A TOR Y A C TION L E TTE R , D IA B L O C A N Y ON P OW E R P L A N T,   UN IT NO. 2 (TAC NO. M D4 150)De ar M r. K een an: Thi s l e tt e r co n fir ms c o mmi tme n ts b y P a ci fic Ga s & E l e ct ri c C o mp a n y (P G&E) i n r e gar d t o Al lo y 82/182 bu tt w el ds in the pre ssu riz er a t D ia bl o C any on Po w er P la nt (D CP P), Un it No. 2.T h e di s c o ve r y, in O c t o b e r 20 0 6 , of f iv e ci r c u m f e r e n t ia l i n d ic a t io n s in t h r e e di s s im il a r m e t a l (D M)w e l d s o n t h e p re ss u ri z e r a t th e W o l f C re e k Ge n e ra ti n g S ta ti o n (W o l f C re e k) r a i se d s a fety con cern s b ase d o n th e s iz e a nd lo cati on of the in di cati ons. A t W ol f C reek, thre e i ndi cati ons w ere in the pre ssu riz er s urge n oz z le-to-sa f e e nd w el d, a nd tw o s epa rate in di cati ons w ere in the safety an d re li ef noz z le-to-sa f e e nd w el ds. Thes e fin di ngs al so in di cate d th at s igni f ic ant conce rns mig ht exist w ith the inspec tion sched ules f or addr essing the pres sur iz er w eld co n ce rn s i ss u e d b y t h e i n d u st ry-s p o n so re d M a te ri a l s R e l i a b i l i ty P ro gra m (M R P), i n "P ri ma ry S y st e m P i p i n g B u tt W e l d I n sp e ct i o n a n d E v a l u a ti o n Gu i d e l i n e (M R P-1 3 9)."The N ucl ear Re gula tory C ommis si on (NR C) is co nce rned ab out the pres suri z er s urge n o z z l e-t o-s a fe e n d w e l d i n d i ca ti o n s, a s th i s i s th e fi rs t ti me t h a t mu l ti p l e c i rc u mfer e n ti a l p ri ma ry w ater str ess-cor ros ion crack ing (PW SCC) indications have been identif ied in a w eld. Th is co n d i ti o n c a l l s i n to qu e st i o n t h e d e gre e o f sa fety ma rgi n p re se n t i n p a st s tr u ct u ra l i n te gri ty ev al uati ons for f la w ed DM w el ds sus cep tib le to PW SC C, si nce mul tip le stre ss-co rrosi on crac king flaw s may grow i nde pen den tly an d u lti matel y grow togethe r, si gnifica ntl y red uci ng the tim e f rom f law ini tiat ion to leak ag e or rupt ure. T he siz e of the relief noz zl e-t o-s af e end f law is al so of conc ern, as thi s flaw ha s a much l arger a spe ct ra tio tha n th ose as sumed i n th e esti mates use d to es tabl is h th e b asi s for co mpl eti ng the ba sel in e i nsp ecti ons requi red by the in dus try-spo nso red M RP. L arger a spe ct ra tio s c oul d re sul t i n a chi ev in g a c riti cal flaw si z e a nd ru p tu re b e fore t h e o n se t o f de te ct a b l e l e a kage. The l ong-term re sol uti on of thi s i ssu e i s e x pec ted to i nv ol v e c han ges to the Ameri can S oci ety of Mech an ic al E ng ine er s Bo ile r and Pr es su r e Ve ss el Co de (A SME Co de), and w ill in volve cha nges to the N RC regul ati ons i n Ti tle 10 of the Co de of F ede ral R egu la tio ns (1 0 C F R), Pa rt 50 , S ecti on 50.5 5a, "Co des an d s tand ards."  The de v el opme nt o f the N RC regul ati ons ,
 
J. S. K een an w heth er th e rule adopts the ASM E Code standar ds or def ines separ ate r eq uirem ents , w ill li k ely ben efit from add iti ona l ope rati ng ex peri enc e, c onti nui ng ass ess ments, and an al y si s b ei ng co n d u ct e d b y t h e N R C a n d t h e M R P. Un til N RC regul ati ons are rev is ed, it is ne ces sary to esta bl is h a mi ni mum se t of en han ced reac tor c ool ant sy stem (R CS) D M bu tt w el d i nsp ecti on ex pec tati ons for ni ckel-b ase d Al lo y 82/182 pre ssu riz er s urge, sp ray , sa f ety , an d re li ef noz z le bu tt w el ds, in cl udi ng safe e nd w elds, t o supplem ent existing inspection and oth er re q uirem ents of the ASM E Code and NRC r e g u l a t i o n s. I n a d d i t i o n , e n h a n c e d m o n i t o r i n g o f R C S l e a ka g e i s n e e d e d t o p r o m p t l y i d e n t i fy any thro ugh-w al l f la w s i n th e p ress uri z er s urge, sp ray , sa f ety , or rel ie f no z z le D M bu tt w el ds or safe en d D M bu tt w el ds to p rev ent add iti ona l degrad ati on f rom o ccu rrin g. The a bov e a cti ons provide reasona ble assura nce tha t the re is no undue risk to the health and saf ety of the public w h i l e t h e N R C r e gul a ti o n s a re r e v i se d. T he NRC comm unicat ed the need f or near-t erm enhancem ents to the indust ry throug h public meeti ngs he ld on N ov embe r 30 , 20 06, De cembe r 20 , 20 06, and F ebru ary 2, 200 7. Li cen see s sub mitted l etters v ol unta ril y co mmitti ng to the enh anc ed in spe cti on and l eakage mon ito rin g r e qu i r e me n t s. A ft e r t e l e c o n fe r e n c e s w i t h s p e c i fi c l i c e n s e e s h e l d b e t w e e n F e b r u a r y 1 2 t h r o u gh Feb ruary 23 , 20 07, the li cen see s s ubmi tted sup pl emen tal co mmitment le tters add ress in g the N R C s t a ff's c o n c e r n s r e ga r d i n g i n s p e c t i o n , c o mp e n s a t o r y a c t i o n s , a n d r e p o r t i n g.In y our le tter d ated F ebru ary 20 , 20 07 (Agenc y w id e D ocu ments Acc ess an d M ana gement System (ADAM S) Acces sion No. M L070580 128), you described act ions y ou w ill tak e at DCPP, U n i t N o. 2 for t h e p re ss u ri z e r d i ss i mi l a r me ta l b u tt w e l d s co n ta i n i n g A l l o y 8 2/1 8 2 ma te ri a l. These commi tments add ress:  1) co mpl eti on sch edu le s for i nsp ecti on/mi tigati on of the w el ds;2) R CS l eak mon ito rin g f requen cy , ac tio n l ev el s, a nd acti ons; 3) repo rtin g require ments, and 4) re i n sp e ct i o n fre que n ci e s. The N RC sta f f ha s re v ie w ed thes e a cti ons an d c ommitmen ts a nd agrees the acti ons an d commi tments are app ropri ate to a ddre ss the pote nti al of PW SC C of the app li cab le pre ssu riz er di ssi mil ar me tal bu tt w el ds con tai ni ng Al lo y 82/182 mate ria l w ith cl ari f ic ati ons on tw o o f the commi tments as in di cate d i n b ol d b el ow regard in g RC S le ak moni tori ng acti on le v el s a nd n o ti fic a ti o n o f ch a n ges t o c o mmi tme n ts.
==SUBJECT:==
* If a qu a n ti ty o f l e a kage c a n b e a ss i gne d t o a s o u rc e o th e r th a n t h e p re ss u ri z e r, a n d t h a t q u a n t it y d e c r e a s e s t h e un id e n t if ie d le a k a g e be lo w b o th thre sho ld s (0.1 gp m [g allon per minut e] st ep increas e or 0.25 gpm above baseline), this w ill n e gat e t h e r e qui re me n t for sh u td o w n a n d/o r p re ss u ri z e r A l l o y 6 0 0/8 2/1 8 2 b u tt w el d b are metal ex ami nati on.*
CONFIRMATORY ACTION LETTER, DIABLO CANYON POWER PLANT, UNIT NO. 2 (TAC NO. MD4150)
PG&E wi ll inf orm the NRC in w riting p ri o r to a n y r e v i si o n o f th e p re ss u ri z e r b u tt w e l d i n sp e ct i o n s ch e d u l e s o r co mmi tme n ts d e sc ri b e d i n t h i s l e tt e r.These cl ari f ic ati ons w ere di scu sse d w ith an d a greed upo n b y y our staff du rin g a te le pho ne di scu ssi on on M arch 8, 200 7, b etw een D onn a J aco bs, Vi ce Pre si den t - N ucl ear Se rv ic es and Mich ele Evan s, Dir ec t or - Divis ion of Com po ne nt In t eg r it y.
 
J. S. K een an Pu rsua nt to S ecti on 182 of the A tomi c E nergy A ct, 4 2 U.S.C. 22 32, y ou are requi red to:1)
==Dear Mr. Keenan:==
No tify me immed ia tel y i f y our und ersta ndi ng di f f ers f rom tha t se t forth ab ov e;2)
 
N o ti fy me i f for a n y r e a so n y o u c a n n o t co mp l e te t h e a ct i o n s a n d c o mmi tme n ts w ithin the spec if ied schedule and advi se me in w riting of y our m odif ied schedule in ad v anc e o f the ch ange; and3)
This letter confirms commitments by Pacific Gas & Electric Company (PG&E) in regard to Alloy 82/182 butt welds in the pressurizer at Diablo Canyon Power Plant (DCPP), Unit No. 2.
N o ti fy me i n w ri ti n g w h e n y o u h a v e c o mp l e te d t h e a ct i o n s a n d c o mmi tme n ts a d d re ss e d i n t h i s C o n fir ma to ry A ct i o n L e tt e r.Issua nce of thi s C onfirmato ry A cti on Lette r do es not prec lu de is sua nce of an ord er formal iz in g the above com mit me nts or req uiring other actions on the part of the licensee; nor does it prec lu de the NR C f rom taki ng en f orce ment acti on f or v io la tio ns of NR C requi rements tha t may have promp ted t he issuance of this letter. In addition, f ailure to tak e the act ions addres sed in thi s C onfirmato ry A cti on Lette r may res ul t i n e nforcement acti on.In a cco rdan ce w ith 10 C FR 2.3 90 of the NR C's "Ru le s o f P racti ce," a c opy of thi s l etter and your respon se w ill be made avail able electr onically f or public inspect ion in the NRC Public Do cumen t R oom or from the N RC's A DA M S, acc ess ib le from the NR C W eb si te a t http://w w w.nrc.gov/read in g-rm/ada ms.html. To th e e x tent pos si bl e, y our resp ons e s hou ld no t in cl ude an y pe rson al pri v acy , pro pri etary , or safeguards in f ormati on so that it can be mad e avail able to the Public w ithout redact ion. If person al priv acy or propr ietar y inf orm ation is nec ess ary to prov id e a n a cce ptab le res pon se, then pl eas e p rov id e a bra cketed cop y of y our resp ons e th at i den tifie s th e i nformatio n th at s hou ld be pro tecte d a nd a re dac ted cop y of y our resp ons e th at d el etes su ch in f ormati on. If y ou request w ith hol di ng of such mate ria l, y ou must specif ically identif y the por tions of y our r espons e that y ou seek to have w ithheld and provide i n deta il the bas es f or your claim of w ithholding (e.g., ex plain w hy the disclosu re of inf orm ation w ill crea te a n u nw arran ted in v asi on of perso nal pri v acy or prov id e th e i nformatio n re quire d b y 10 CF R 2.39 0(b) to s upp ort a reque st for w ith hol di ng con f id enti al co mmerci al or f in anc ia l in f ormati on). If safeg uard s i nformatio n i s n ece ssa ry to prov id e a n a cce ptab le res pon se, pl eas e prov id e th e l ev el of pro tecti on des cri bed i n 1 0 C FR 73.21.
The discovery, in October 2006, of five circumferential indications in three dissimilar metal (DM) welds on the pressurizer at the Wolf Creek Generating Station (Wolf Creek) raised safety concerns based on the size and location of the indications. At Wolf Creek, three indications were in the pressurizer surge nozzle-to-safe end weld, and two separate indications were in the safety and relief nozzle-to-safe end welds. These findings also indicated that significant concerns might exist with the inspection schedules for addressing the pressurizer weld concerns issued by the industry-sponsored Materials Reliability Program (MRP), in Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139).
Sin ce r ely,/R A/
The Nuclear Regulatory Commission (NRC) is concerned about the pressurizer surge nozzle-to-safe end weld indications, as this is the first time that multiple circumferential primary water stress-corrosion cracking (PWSCC) indications have been identified in a weld. This condition calls into question the degree of safety margin present in past structural integrity evaluations for flawed DM welds susceptible to PWSCC, since multiple stress-corrosion cracking flaws may grow independently and ultimately grow together, significantly reducing the time from flaw initiation to leakage or rupture. The size of the relief nozzle-to-safe end flaw is also of concern, as this flaw has a much larger aspect ratio than those assumed in the estimates used to establish the basis for completing the baseline inspections required by the industry-sponsored MRP. Larger aspect ratios could result in achieving a critical flaw size and rupture before the onset of detectable leakage.
J. E. D y e r, D i re ct o r Of f ic e o f N ucl ear Re acto r R egul ati on Do cket No. 50-323Li cen se No. D PR-82 c c: S e e n e x t p a ge J. S. K een an Pu rsua nt to S ecti on 182 of the A tomi c E nergy A ct, 4 2 U.S.C. 22 32, y ou are requi red to:1)
The long-term resolution of this issue is expected to involve changes to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), and will involve changes to the NRC regulations in Title 10 of the Code of Federal Regulations (10 CFR),
No tify me immed ia tel y i f y our und ersta ndi ng di f f ers f rom tha t se t forth ab ov e;2)
Part 50, Section 50.55a, Codes and standards. The development of the NRC regulations,
N o ti fy me i f for a n y r e a so n y o u c a n n o t co mp l e te t h e a ct i o n s a n d c o mmi tme n ts w ithin the spec if ied schedule and advi se me in w riting of y our m odif ied schedule in ad v anc e o f the ch ange; and3)
 
N o ti fy me i n w ri ti n g w h e n y o u h a v e c o mp l e te d t h e a ct i o n s a n d c o mmi tme n ts a d d re ss e d i n t h i s C o n fir ma to ry A ct i o n L e tt e r.Issua nce of thi s C onfirmato ry A cti on Lette r do es not prec lu de is sua nce of an ord er formal iz in g the above com mit me nts or req uiring other actions on the part of the licensee; nor does it prec lu de the NR C f rom taki ng en f orce ment acti on f or v io la tio ns of NR C requi rements tha t may have promp ted t he issuance of this letter. In addition, f ailure to tak e the act ions addres sed in thi s C onfirmato ry A cti on Lette r may res ul t i n e nforcement acti on.In a cco rdan ce w ith 10 C FR 2.3 90 of the NR C's "Ru le s o f P racti ce," a c opy of thi s l etter and your respon se w ill be made avail able electr onically f or public inspect ion in the NRC Public Do cumen t R oom or from the N RC's A DA M S, acc ess ib le from the NR C W eb si te a t http://w w w.nrc.gov/read in g-rm/ada ms.html. To th e e x tent pos si bl e, y our resp ons e s hou ld no t in cl ude an y pe rson al pri v acy , pro pri etary , or safeguards in f ormati on so that it can be mad e avail able to the Public w ithout redact ion. If person al priv acy or propr ietar y inf orm ation is nec ess ary to prov id e a n a cce ptab le res pon se, then pl eas e p rov id e a bra cketed cop y of y our resp ons e th at i den tifie s th e i nformatio n th at s hou ld be pro tecte d a nd a re dac ted cop y of y our resp ons e th at d el etes su ch in f ormati on. If y ou request w ith hol di ng of such mate ria l, y ou must specif ically identif y the por tions of y our r espons e that y ou seek to have w ithheld and provide i n deta il the bas es f or your claim of w ithholding (e.g., ex plain w hy the disclosu re of inf orm ation w ill crea te a n u nw arran ted in v asi on of perso nal pri v acy or prov id e th e i nformatio n re quire d b y 10 CF R 2.39 0(b) to s upp ort a reque st for w ith hol di ng con f id enti al co mmerci al or f in anc ia l in f ormati on). If safeg uard s i nformatio n i s n ece ssa ry to prov id e a n a cce ptab le res pon se, pl eas e prov id e th e l ev el of pro tecti on des cri bed i n 1 0 C FR 73.21.
J. S. Keenan                                      whether the rule adopts the ASME Code standards or defines separate requirements, will likely benefit from additional operating experience, continuing assessments, and analysis being conducted by the NRC and the MRP.
Sin ce r ely,/RA/
Until NRC regulations are revised, it is necessary to establish a minimum set of enhanced reactor coolant system (RCS) DM butt weld inspection expectations for nickel-based Alloy 82/182 pressurizer surge, spray, safety, and relief nozzle butt welds, including safe end welds, to supplement existing inspection and other requirements of the ASME Code and NRC regulations. In addition, enhanced monitoring of RCS leakage is needed to promptly identify any through-wall flaws in the pressurizer surge, spray, safety, or relief nozzle DM butt welds or safe end DM butt welds to prevent additional degradation from occurring. The above actions provide reasonable assurance that there is no undue risk to the health and safety of the public while the NRC regulations are revised.
J. E. D y e r, D i re ct o r Of f ic e o f N ucl ear Re acto r R egul ati on Do cket No. 50-323 Li cen se No. D PR-82 c c:  S e e n e x t p a ge Dist ribu tion: PU BLI C LPL IV R/F Rid sNr rP M AW ang Rid sNr rLA LFei z ollah i Rid sNr rD orlL pl4 Rid sO gcR p Rid sAcr sAcnw M ailC ente r Rid sRg n4M ailC ente r Rids NrrOd Rid sNr rD orl Rid sNr rD ci Rid sO EM ailC ente r Rid sEdo M ailC ente r DC ulliso n, ED O R IV VD ricks, O PA , R IVW M aler , S tat e Li aison O ffi cer, R IV Rid sNr rD irs TLupold , NRR ESull ivan, NRR RPasc arel li, NRR Rid sNr rD ciCp nb Rid sNr rA des A DA MS A ccess ion N o. ML070670425 OFFIC E CPN B DC I LPL4/PM LPL4/LA LPL4/BC TECH ED DIR S/TA NAM E TLu po ld ESulli va n AW an g LFe iz oll ah i DTe ra o HC ha ng RPa scare lli DATE 3/1 3/0 7 3/1 3/0 7 3/1 2/0 7 3/9/07 3/1 2/0 7 2/2 8/0 7 3/1 2/0 7 OF FI C E C PN B/BC D R P/D R GN 4 D OR L/D D C I/D AD ES/AD N R R/D NAM E TCh an AHo w ell , III CH an ey M Eva ns JGro be JDy er DATE 3/1 4/0 7 3/1 4/0 7 3/1 9/0 7 3/1 4/0 7 3/1 4/0 7 3/1 5/0 7OFFICIAL RECORD CO PY Jan uary 20 07 Di abl o C any on Po w er P la nt, U ni ts 1 an d 2 cc: NR C Re si den t Ins pec tor Di abl o C any on Po w er P la nt c/o U.S. N ucl ear Re gula tory C ommis si on P.O. B ox 36 9 Av il a B eac h, C A  93 424 Si erra Cl ub Sa n L uci a C hap ter ATTN: An drew C hri sti e P.O. B ox 15 755 Sa n L ui s Obi spo , C A  93 406 M s. N anc y C ul v er Sa n L ui s Obi spo  M othe rs for P eac e P.O. B ox 16 4 Pi smo B eac h, C A  93 448 Ch ai rman S a n L u i s Ob i sp o C o u n ty    B o a rd o f S u p e rv i so rs 105 5 M onte rey S treet, Su ite D 430 Sa n L ui s Obi spo , C A  93 408 M r. Truman Bu rns M r. R obe rt K in osi an Ca li f orni a P ubl ic U til iti es Co mmissi on 505 V an Ne ss, Ro om 4 102 Sa n F ranc is co, CA  941 02 D i a b l o C a n y o n I n d e p e n d e n t S a fety  C ommitte e A TTN:  R o b e r t R. W e l l i n gt o n , E s q.            Le gal Co uns el 857 C ass S treet, Su ite D M onte rey , C A  93 940 R e gi o n a l A d mi n i st ra to r, R e gi o n I V U.S. N ucl ear Re gula tory C ommis si on Ha rris Tow er & P av il li on 611 R y an Pl az a D riv e, S ui te 4 00 Arl in gton, TX  76 011-806 4 A n t o n i o F e r nán d e z , E s q.Pa ci f ic Gas & El ectri c C ompa ny P.O. B ox 74 42 Sa n F ranc is co, CA  941 20 Ci ty E di tor The Trib une 382 5 S outh H igue ra S treet P.O. B ox 11 2 Sa n L ui s Obi spo , C A  93 406-011 2 Di recto r, R adi ol ogic He al th B ranc h Sta te D epa rtment o f H eal th S erv ic es P.O. B ox 99 741 4, M S 761 0 Sa cramen to, C A  95 899-741 4 M r. Ja mes D. B oy d, C ommis si one r Ca li f orni a E nergy C ommis si on 151 6 N in th S treet (M S 31)Sa cramen to, C A  95 814 M r. Ja mes R. B ecker, V ic e P resi den t Di abl o C any on Operati ons    an d S tati on Di recto r Di abl o C any on Po w er P la nt P.O. B ox 56 Av il a B eac h, C A  93 424 Jen ni f er Tan g Fie ld Re pr es en t at ive Un ite d S tates S ena tor B arba ra B ox er 170 0 M ontgomery S treet, Su ite 24 0 Sa n F ranc is co, CA  941 11}}
The NRC communicated the need for near-term enhancements to the industry through public meetings held on November 30, 2006, December 20, 2006, and February 2, 2007. Licensees submitted letters voluntarily committing to the enhanced inspection and leakage monitoring requirements. After teleconferences with specific licensees held between February 12 through February 23, 2007, the licensees submitted supplemental commitment letters addressing the NRC staffs concerns regarding inspection, compensatory actions, and reporting.
In your letter dated February 20, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML070580128), you described actions you will take at DCPP, Unit No. 2 for the pressurizer dissimilar metal butt welds containing Alloy 82/182 material.
These commitments address: 1) completion schedules for inspection/mitigation of the welds;
: 2) RCS leak monitoring frequency, action levels, and actions; 3) reporting requirements, and
: 4) reinspection frequencies.
The NRC staff has reviewed these actions and commitments and agrees the actions and commitments are appropriate to address the potential of PWSCC of the applicable pressurizer dissimilar metal butt welds containing Alloy 82/182 material with clarifications on two of the commitments as indicated in bold below regarding RCS leak monitoring action levels and notification of changes to commitments.
* If a quantity of leakage can be assigned to a source other than the pressurizer, and that quantity decreases the unidentified leakage below both thresholds (0.1 gpm [gallon per minute] step increase or 0.25 gpm above baseline), this will negate the requirement for shutdown and/or pressurizer Alloy 600/82/182 butt weld bare metal examination.
* PG&E will inform the NRC in writing prior to any revision of the pressurizer butt weld inspection schedules or commitments described in this letter.
These clarifications were discussed with and agreed upon by your staff during a telephone discussion on March 8, 2007, between Donna Jacobs, Vice President - Nuclear Services and Michele Evans, Director - Division of Component Integrity.
 
J. S. Keenan                                      Pursuant to Section 182 of the Atomic Energy Act, 42 U.S.C. 2232, you are required to:
: 1)    Notify me immediately if your understanding differs from that set forth above;
: 2)     Notify me if for any reason you cannot complete the actions and commitments within the specified schedule and advise me in writing of your modified schedule in advance of the change; and
: 3)    Notify me in writing when you have completed the actions and commitments addressed in this Confirmatory Action Letter.
Issuance of this Confirmatory Action Letter does not preclude issuance of an order formalizing the above commitments or requiring other actions on the part of the licensee; nor does it preclude the NRC from taking enforcement action for violations of NRC requirements that may have prompted the issuance of this letter. In addition, failure to take the actions addressed in this Confirmatory Action Letter may result in enforcement action.
In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and your response will be made available electronically for public inspection in the NRC Public Document Room or from the NRCs ADAMS, accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. To the extent possible, your response should not include any personal privacy, proprietary, or safeguards information so that it can be made available to the Public without redaction. If personal privacy or proprietary information is necessary to provide an acceptable response, then please provide a bracketed copy of your response that identifies the information that should be protected and a redacted copy of your response that deletes such information. If you request withholding of such material, you must specifically identify the portions of your response that you seek to have withheld and provide in detail the bases for your claim of withholding (e.g., explain why the disclosure of information will create an unwarranted invasion of personal privacy or provide the information required by 10 CFR 2.390(b) to support a request for withholding confidential commercial or financial information). If safeguards information is necessary to provide an acceptable response, please provide the level of protection described in 10 CFR 73.21.
Sincerely,
                                                /RA/
J. E. Dyer, Director Office of Nuclear Reactor Regulation Docket No. 50-323 License No. DPR-82 cc: See next page
 
ML070670425 OFFICE      CPNB          DCI          LPL4/PM      LPL4/LA      LPL4/BC        TECH ED        DIRS/TA NAME        TLupold        ESullivan    AWang        LFeizollahi  DTerao          HChang        RPascarelli DATE        3/13/07        3/13/07      3/12/07      3/9/07      3/12/07        2/28/07        3/12/07 OFFICE      CPNB/BC        DRP/D RGN4  DORL/D      DCI/D        ADES/AD        NRR/D NAME        TChan          AHowell, III CHaney      MEvans        JGrobe          JDyer DATE        3/14/07        3/14/07      3/19/07      3/14/07      3/14/07        3/15/07 Diablo Canyon Power Plant, Units 1 and 2 cc:
NRC Resident Inspector                  Antonio Fernández, Esq.
Diablo Canyon Power Plant                Pacific Gas & Electric Company c/o U.S. Nuclear Regulatory Commission  P.O. Box 7442 P.O. Box 369                            San Francisco, CA 94120 Avila Beach, CA 93424 City Editor Sierra Club San Lucia Chapter            The Tribune ATTN: Andrew Christie                    3825 South Higuera Street P.O. Box 15755                          P.O. Box 112 San Luis Obispo, CA 93406                San Luis Obispo, CA 93406-0112 Ms. Nancy Culver                        Director, Radiologic Health Branch San Luis Obispo                          State Department of Health Services Mothers for Peace                      P.O. Box 997414, MS 7610 P.O. Box 164                            Sacramento, CA 95899-7414 Pismo Beach, CA 93448 Mr. James D. Boyd, Commissioner Chairman                                California Energy Commission San Luis Obispo County                  1516 Ninth Street (MS 31)
Board of Supervisors                  Sacramento, CA 95814 1055 Monterey Street, Suite D430 San Luis Obispo, CA 93408                Mr. James R. Becker, Vice President Diablo Canyon Operations Mr. Truman Burns                          and Station Director Mr. Robert Kinosian                      Diablo Canyon Power Plant California Public Utilities Commission  P.O. Box 56 505 Van Ness, Room 4102                  Avila Beach, CA 93424 San Francisco, CA 94102 Jennifer Tang Diablo Canyon Independent Safety        Field Representative Committee                              United States Senator Barbara Boxer ATTN: Robert R. Wellington, Esq.         1700 Montgomery Street, Suite 240 Legal Counsel                  San Francisco, CA 94111 857 Cass Street, Suite D Monterey, CA 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 January 2007}}

Latest revision as of 19:14, 13 March 2020

Confirmatory Action Letter Alloy 82/182 Pressurizer Butt Welds
ML070670425
Person / Time
Site: Diablo Canyon Pacific Gas & Electric icon.png
Issue date: 03/15/2007
From: Dyer J
Office of Nuclear Reactor Regulation
To: Keenan J
Pacific Gas & Electric Co
Wang, A B, NRR/DORL/LPLIV, 415-1445
References
TAC MD4150, NRR-07-003
Download: ML070670425 (5)
v • d • e


Text

March 15, 2007 CAL No. NRR-07-003 Mr. John S. Keenan Senior Vice President and Chief Nuclear Office Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 770000, Mail Code B32 San Francisco, CA 94177-0001

SUBJECT:

CONFIRMATORY ACTION LETTER, DIABLO CANYON POWER PLANT, UNIT NO. 2 (TAC NO. MD4150)

Dear Mr. Keenan:

This letter confirms commitments by Pacific Gas & Electric Company (PG&E) in regard to Alloy 82/182 butt welds in the pressurizer at Diablo Canyon Power Plant (DCPP), Unit No. 2.

The discovery, in October 2006, of five circumferential indications in three dissimilar metal (DM) welds on the pressurizer at the Wolf Creek Generating Station (Wolf Creek) raised safety concerns based on the size and location of the indications. At Wolf Creek, three indications were in the pressurizer surge nozzle-to-safe end weld, and two separate indications were in the safety and relief nozzle-to-safe end welds. These findings also indicated that significant concerns might exist with the inspection schedules for addressing the pressurizer weld concerns issued by the industry-sponsored Materials Reliability Program (MRP), in Primary System Piping Butt Weld Inspection and Evaluation Guideline (MRP-139).

The Nuclear Regulatory Commission (NRC) is concerned about the pressurizer surge nozzle-to-safe end weld indications, as this is the first time that multiple circumferential primary water stress-corrosion cracking (PWSCC) indications have been identified in a weld. This condition calls into question the degree of safety margin present in past structural integrity evaluations for flawed DM welds susceptible to PWSCC, since multiple stress-corrosion cracking flaws may grow independently and ultimately grow together, significantly reducing the time from flaw initiation to leakage or rupture. The size of the relief nozzle-to-safe end flaw is also of concern, as this flaw has a much larger aspect ratio than those assumed in the estimates used to establish the basis for completing the baseline inspections required by the industry-sponsored MRP. Larger aspect ratios could result in achieving a critical flaw size and rupture before the onset of detectable leakage.

The long-term resolution of this issue is expected to involve changes to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code), and will involve changes to the NRC regulations in Title 10 of the Code of Federal Regulations (10 CFR),

Part 50, Section 50.55a, Codes and standards. The development of the NRC regulations,

J. S. Keenan whether the rule adopts the ASME Code standards or defines separate requirements, will likely benefit from additional operating experience, continuing assessments, and analysis being conducted by the NRC and the MRP.

Until NRC regulations are revised, it is necessary to establish a minimum set of enhanced reactor coolant system (RCS) DM butt weld inspection expectations for nickel-based Alloy 82/182 pressurizer surge, spray, safety, and relief nozzle butt welds, including safe end welds, to supplement existing inspection and other requirements of the ASME Code and NRC regulations. In addition, enhanced monitoring of RCS leakage is needed to promptly identify any through-wall flaws in the pressurizer surge, spray, safety, or relief nozzle DM butt welds or safe end DM butt welds to prevent additional degradation from occurring. The above actions provide reasonable assurance that there is no undue risk to the health and safety of the public while the NRC regulations are revised.

The NRC communicated the need for near-term enhancements to the industry through public meetings held on November 30, 2006, December 20, 2006, and February 2, 2007. Licensees submitted letters voluntarily committing to the enhanced inspection and leakage monitoring requirements. After teleconferences with specific licensees held between February 12 through February 23, 2007, the licensees submitted supplemental commitment letters addressing the NRC staffs concerns regarding inspection, compensatory actions, and reporting.

In your letter dated February 20, 2007 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML070580128), you described actions you will take at DCPP, Unit No. 2 for the pressurizer dissimilar metal butt welds containing Alloy 82/182 material.

These commitments address: 1) completion schedules for inspection/mitigation of the welds;

2) RCS leak monitoring frequency, action levels, and actions; 3) reporting requirements, and
4) reinspection frequencies.

The NRC staff has reviewed these actions and commitments and agrees the actions and commitments are appropriate to address the potential of PWSCC of the applicable pressurizer dissimilar metal butt welds containing Alloy 82/182 material with clarifications on two of the commitments as indicated in bold below regarding RCS leak monitoring action levels and notification of changes to commitments.

  • If a quantity of leakage can be assigned to a source other than the pressurizer, and that quantity decreases the unidentified leakage below both thresholds (0.1 gpm [gallon per minute] step increase or 0.25 gpm above baseline), this will negate the requirement for shutdown and/or pressurizer Alloy 600/82/182 butt weld bare metal examination.
  • PG&E will inform the NRC in writing prior to any revision of the pressurizer butt weld inspection schedules or commitments described in this letter.

These clarifications were discussed with and agreed upon by your staff during a telephone discussion on March 8, 2007, between Donna Jacobs, Vice President - Nuclear Services and Michele Evans, Director - Division of Component Integrity.

J. S. Keenan Pursuant to Section 182 of the Atomic Energy Act, 42 U.S.C. 2232, you are required to:

1) Notify me immediately if your understanding differs from that set forth above;
2) Notify me if for any reason you cannot complete the actions and commitments within the specified schedule and advise me in writing of your modified schedule in advance of the change; and
3) Notify me in writing when you have completed the actions and commitments addressed in this Confirmatory Action Letter.

Issuance of this Confirmatory Action Letter does not preclude issuance of an order formalizing the above commitments or requiring other actions on the part of the licensee; nor does it preclude the NRC from taking enforcement action for violations of NRC requirements that may have prompted the issuance of this letter. In addition, failure to take the actions addressed in this Confirmatory Action Letter may result in enforcement action.

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and your response will be made available electronically for public inspection in the NRC Public Document Room or from the NRCs ADAMS, accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. To the extent possible, your response should not include any personal privacy, proprietary, or safeguards information so that it can be made available to the Public without redaction. If personal privacy or proprietary information is necessary to provide an acceptable response, then please provide a bracketed copy of your response that identifies the information that should be protected and a redacted copy of your response that deletes such information. If you request withholding of such material, you must specifically identify the portions of your response that you seek to have withheld and provide in detail the bases for your claim of withholding (e.g., explain why the disclosure of information will create an unwarranted invasion of personal privacy or provide the information required by 10 CFR 2.390(b) to support a request for withholding confidential commercial or financial information). If safeguards information is necessary to provide an acceptable response, please provide the level of protection described in 10 CFR 73.21.

Sincerely,

/RA/

J. E. Dyer, Director Office of Nuclear Reactor Regulation Docket No. 50-323 License No. DPR-82 cc: See next page

ML070670425 OFFICE CPNB DCI LPL4/PM LPL4/LA LPL4/BC TECH ED DIRS/TA NAME TLupold ESullivan AWang LFeizollahi DTerao HChang RPascarelli DATE 3/13/07 3/13/07 3/12/07 3/9/07 3/12/07 2/28/07 3/12/07 OFFICE CPNB/BC DRP/D RGN4 DORL/D DCI/D ADES/AD NRR/D NAME TChan AHowell, III CHaney MEvans JGrobe JDyer DATE 3/14/07 3/14/07 3/19/07 3/14/07 3/14/07 3/15/07 Diablo Canyon Power Plant, Units 1 and 2 cc:

NRC Resident Inspector Antonio Fernández, Esq.

Diablo Canyon Power Plant Pacific Gas & Electric Company c/o U.S. Nuclear Regulatory Commission P.O. Box 7442 P.O. Box 369 San Francisco, CA 94120 Avila Beach, CA 93424 City Editor Sierra Club San Lucia Chapter The Tribune ATTN: Andrew Christie 3825 South Higuera Street P.O. Box 15755 P.O. Box 112 San Luis Obispo, CA 93406 San Luis Obispo, CA 93406-0112 Ms. Nancy Culver Director, Radiologic Health Branch San Luis Obispo State Department of Health Services Mothers for Peace P.O. Box 997414, MS 7610 P.O. Box 164 Sacramento, CA 95899-7414 Pismo Beach, CA 93448 Mr. James D. Boyd, Commissioner Chairman California Energy Commission San Luis Obispo County 1516 Ninth Street (MS 31)

Board of Supervisors Sacramento, CA 95814 1055 Monterey Street, Suite D430 San Luis Obispo, CA 93408 Mr. James R. Becker, Vice President Diablo Canyon Operations Mr. Truman Burns and Station Director Mr. Robert Kinosian Diablo Canyon Power Plant California Public Utilities Commission P.O. Box 56 505 Van Ness, Room 4102 Avila Beach, CA 93424 San Francisco, CA 94102 Jennifer Tang Diablo Canyon Independent Safety Field Representative Committee United States Senator Barbara Boxer ATTN: Robert R. Wellington, Esq. 1700 Montgomery Street, Suite 240 Legal Counsel San Francisco, CA 94111 857 Cass Street, Suite D Monterey, CA 93940 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower & Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 January 2007

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