Information Notice 2007-06, Potential Common Cause Vulnerabilities in Essential Service Water Systems: Difference between revisions

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{{#Wiki_filter:UNIT ED STAT ES N U C L E A R R E GU L A TOR Y C OM M IS S ION OF F IC E OF N U C L E A R R E A C TOR R E GU L A TION W AS HIN GT ON, D.C. 205 55-0 001 Feb ruary 9, 200 7 NRC INFORMATI
{{#Wiki_filter:UNITED STATES


ON NO T ICE 2007-06: 
===NUCLEAR REGULATORY COMMISSION===
POT ENT IAL CO M M ON CAUSE
OFFICE OF NUCLEAR REACTOR REGULATION


VULNERABILI
WASHINGTON, D.C. 20555-0001


===T IES IN ESSENT===
===February 9, 2007===
IAL SERVICE
NRC INFORMATION NOTICE 2007-06:  POTENTIAL COMMON CAUSE


W A T E R SY S T E MS A DDRESSEES All hol de r s o f ope r at ing lice ns ee s f or nuc lea r powe r re ac t or s, exce pt th os e who have perman entl y ce ase d o pera tio ns and ha v e c erti f ie d th at fuel ha s b een pe rmanen tly remo v ed f rom the reac tor v essel.
VULNERABILITIES IN ESSENTIAL SERVICE
 
===WATER SYSTEMS===
 
==ADDRESSEES==
All holders of operating licensees for nuclear power reactors, except those who have
 
permanently ceased operations and have certified that fuel has been permanently removed
 
from the reactor vessel.


==PURPOSE==
==PURPOSE==
The U.S. N u cl e a r R e gul a to ry C o mmi ss i o n (N R C) i s i ss u i n g th i s i n form a ti o n n o ti ce (IN) to a l e rt add ress ees of the i mportan ce of main tai ni ng ess enti al se rv ic e w ater (ES W) sy stems in a ma n n e r th a t p re cl u d e s th e d e v e l o p me n t o f po te n ti a l c o mmo n c a u se fai l u re v u l n e ra b i l i ti e s d u e t o pi pi ng or hea t ex cha nger d egrada tio n.  It i s e x pec ted that reci pi ents w il l rev ie w the i nformatio n for a p p l i ca b i l i ty t o t h e i r fac i l i ti e s a n d c o n si d e r a ct i o n s, a s a p p ro p ri a te , to a v o i d s i mi l a r p ro b l e ms. How ever, sug g est ions conta
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert
 
addressees of the importance of maintaining essential service water (ESW) systems in a
 
manner that precludes the development of potential common cause failure vulnerabilities due to
 
piping or heat exchanger degradation.  It is expected that recipients will review the information
 
for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.
 
However, suggestions contained in this IN are not NRC requirements; therefore, no specific
 
action or written response is required.
 
==DESCRIPTION OF CIRCUMSTANCES==
There have been two events at foreign operating reactors in which external corrosion of piping
 
located in vaults has caused a catastrophic loss of one train of the ESW system.  These two
 
events also had common cause failure aspects that were identified as part of the extent-of- condition reviews.  The first foreign event occurred at a pressurized-water reactor (PWR)
designed by Westinghouse, that began commercial operation in 1988.  On August 25, 2004, while operating at 100 percent power, an ESW system manhole pipe broke circumferentially
 
prompting a plant shutdown from the total loss of the B train of the ESW system.  The event
 
was of great concern for plant safety because it could have led to a common cause failure in a
 
system that is the ultimate heat sink for most safety loads.  The ESW pipes are buried and use
 
manholes at certain intervals to allow for inspection and maintenance.  The ESW piping is a
 
BONNA design that uses a steel pipe lined with cement on both sides to prevent corrosion.
 
The manhole filled with surface water and corroded the exposed carbon steel manhole piping
 
neck.  The break resulted from external corrosion due to improper installation of external
 
cement pipe coating.  The licensee extent-of-condition review found corrosion at two other
 
ESW manhole necks that also required significant repair.
 
The second foreign event occurred at a PWR, designed by Framatome, that began commercial
 
operation in 1988.  On December 11, 1998, while operating at 75 percent power, an ESW pipe
 
ruptured and flooded the piping gallery with sea water.  Since the B train of the ESW system
 
was lost, the operators shutdown the plant.  The pipe is composed of prestressed, inner and
 
outer concrete pipes with embedded strings and steel pipe.  A visual inspection of the failed
 
pipe revealed a 3.3 foot long by 2.8 inches wide through-wall rupture.  The prestressed wire
 
and steel cylinder were found to be severely corroded.  The pipe is located in an underground
 
gallery that has very humid conditions.  The licensee determined that condensation got inside a
 
small crack on the surface of the pipe causing corrosion of the steel wire.  The licensee extent- of-condition review identified 16 other pipe spools that were also replaced.
 
There also have been two events at domestic operating reactor plants that experienced
 
significant internal degradation of critical ESW components that had the potential for common
 
cause failures.  On June 27, 2005, at the South Texas Project, Unit 2, a three gallons/hour
 
through-wall leak was identified in Train 2A, essential cooling water (ECW) system piping
 
flange.  The pipe is 30 inches in diameter, composed of an aluminum-bronze, and is located
 
immediately downstream of an ECW return throttle (butterfly) valve.  Subsequent licensee
 
investigation found cavitation pitting, circumferential pipe cracking, and pipe-to-end flange weld
 
separation in the pipe.  On August 15, 2005, as part of their extent-of-condition review, the
 
licensee inspected Train 2B of the ECW system and determined that a similar downstream
 
flange had an approximately 30 inches-long by three inches-wide segment of the aluminum- bronze pipe that broke free.  Train 2B of the ECW system was declared inoperable for the
 
same reasons as ECW Train 2A and was reported to the NRC as a common-cause
 
inoperability of independent trains (Licensee Event Report No. 499/2005004, Agencywide
 
Documents Access and Management System (ADAMS) Accession No. ML052630031).  The
 
licensee determined the cause of the damage was cavitation impingement from the heavily
 
throttled butterfly valve.  The root cause was the failure to incorporate requisite inspection
 
activities for ECW piping into station programs.
 
On March 20, 2005, at Point Beach Nuclear Plant, Unit 1, the G-01 emergency diesel generator
 
(EDG) became inoperable due to a through-wall leak in the endbell of the EDG cooling system
 
heat exchanger (Inspection Report 50-266/2005-010, ADAMS Accession No. ML053000237).
 
Licensee inspections identified significant damage to the endbell due to microbiologically
 
induced corrosion (MIC).  The licensee maintenance rule evaluation determined that the poor
 
condition of the endbells from pitting caused by MIC was known for nearly ten years, but timely
 
and effective corrective actions were not taken.  Also, on April 22, 2005, a through-wall service
 
water (SW) leak occurred on the G-02 EDG heat exchanger alternate SW supply line due to
 
MIC.
 
==BACKGROUND==
The ESW system (or its equivalent) for U. S. commercial reactor plants is the assured, safety- related means of transferring sensible and decay heat from the reactor coolant system to the
 
ultimate heat sink.  The ESW system is also relied upon for other critical safety functions, such
 
as providing cooling water for most of the essential, safety-related equipment used for
 
mitigating plant accident and transient conditions, reactor coolant pump seal cooling, spent fuel
 
pool cooling, and for dissipating sensible and reactor decay heat during shutdown conditions. Also, on PWRs, the safety related auxiliary feedwater systems typically rely on the ESW system
 
as an emergency makeup water source for feeding the steam generators.  Plant-specific
 
probabilistic risk assessments (PRAs) have shown that the loss of the ESW system may be a


ined in this IN ar
significant contributor to the potential for a core damage accident.


e not NRC req
==DISCUSSION==
The first foreign event involved the failure to properly protect the exterior piping surfaces in the


uirem ents; the ref ore, no specif
vicinity of weld neck flanges that had been installed to allow personnel access for inspecting the


ic acti on or w ritte n re spo nse i s re quire d.DESCRIPTION O
inside ESW system piping surfaces. The unprotected weld neck joints were subject to


F CIRCUMSTA
corrosion.  All of these areas were also subject to routine wetting of the unprotected exterior


NCES There hav e b een tw o e v ents at f orei gn op erati ng rea ctors in w hi ch ex terna l corro si on of pi pi ng lo c a t e d in va u lt s ha s ca u s e d a c a t a s t r o p h ic lo s s of on e t r a in of t h e ES W sy s t e m.  T h e s e t wo e v e n t s a l s o h a d c o m m o n c a u s e f a i l u r e a s p e c t s t h a t w e r e i d e n t i fi e d a s p a r t o f t h e e x t e n t-o f-condit ion revi ew s.  T he f irst f oreig n ev ent occ urr ed at a press
surface of weld neck areas.  In addition, NRC staff concluded that a fundamental shortcoming


urized-water re
associated with the first foreign event was the utilitys failure to adequately trend and take


act or (PW R)des igne d b y W esti nghou se, that began co mmerci al op erati on in 19 88.  On Au gust 25 , 20 04, w hile operating
appropriate corrective action for a known degraded condition.  Domestic operating reactor


at 100 perce
plants are subject to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B,
Criterion XVI, Corrective Action, which requires that prompt and effective corrective actions be


nt power, an ESW
taken to address significant conditions adverse to quality.


sy ste m m anhole pipe brok
The second foreign event also involved the failure to protect the exterior piping surface of the


e circum f eren tially prompti ng a pl ant shu tdow n from the
ESW system.  One of the lessons learned was to implement an inspection program that


tota l lo ss of the B trai n o f the E SW sy stem.  The e v ent w as of g reat con cern for pl ant safety be cau se it cou ld ha v e l ed to a co mmon c aus e fai lu re i n a sy stem th at i s th e u lti mate hea t si nk f or mo st s afety l oad s.  The E SW pi pes are bu rie d a nd use manh ol es at c ertai n i nterv al s to al lo w for i nsp ecti on and mai nten anc e.  The E SW pi pi ng i s a B ON N A d e si gn th a t u se s a s te e l p i p e l i n e d w i th c e me n t o n b o th s i d e s to p re v e n t co rr o si o n. The man hol e fil le d w ith su rf ace w ater and co rrode d th e e x pos ed carb on stee l manh ol e p ip in g nec k.  The b reak res ul ted f rom e x terna l corro si on due to imp rope r i nsta ll ati on of ex terna l cemen t pi pe coa tin g.  The l ic ens ee ex tent-o f-con di tio n re v ie w found co rrosi on at tw o o ther E S W ma n h o l e n e cks t h a t a l so r e qui re d s i gni fic a n t re p a i r. The s eco nd f orei gn ev ent occ urred at a P W R, des igne d b y F ramatome , tha t be gan co mmerci al ope rati on in 19 88.  On De cembe r 11 , 19 98, w hi le op erati ng at 75 perc ent pow er, a n E SW pi pe ruptu red and floo ded the pi pi ng gall ery w ith se a w ater.  S in ce the B trai n o f the E SW sy stem w as lo st, th e o pera tors shu tdow n th e p la nt.  The p ip e i s c ompo sed of pre stress ed, in ner and M L06 284 060 8 IN 200 7-06 P a g e 2 o f 5 oute r co ncre te p ip es w ith emb edd ed stri ngs an d s teel pi pe.  A v is ual i nsp ecti on of the f ai le d p i p e r e v e a l e d a 3.3 foo t l o n g b y 2.8 i n ch e s w i d e t h ro u gh-w a l l r u p tu re.  Th e p re st re ss e d w i re and ste el cy li nde r w ere f oun d to be se v erel y co rrode d.  The p ip e i s l oca ted in an un dergroun d gall ery tha t ha s v ery hu mid co ndi tio ns.  The li cen see de termin ed that con den sati on got i nsi de a sm a l l c ra ck o n t h e s u rfac e o f th e p i p e c a u si n g c o rr o si o n o f th e s te e l w i re.  Th e l i ce n se e e x te n t-o f-co n d i ti o n r e v i e w i d e n ti fie d 1 6 o th e r p i p e s p o o l s th a t w e re a l so r e p l a ce d. There al so hav e b een tw o e v ents at dome sti c o pera tin g reacto r pl ants tha t ex peri enc ed si gnifica nt i ntern al de gradati on of criti cal E SW co mpon ents tha t ha d th e p oten tia l f or c ommon cau se f ai lu res.  On Jun e 2 7, 2 005 , at the So uth Tex as Pro ject, U ni t 2, a th ree gall ons/hou r throu gh-w al l le ak w as id enti f ie d i n Trai n 2 A, ess enti al co ol in g w ater (EC W) sy stem p ip in g f la nge.  The p ip e i s 3 0 i nch es in di ameter, compo sed of an al umi num-bro nz e, a nd is l oca ted immed ia tel y do w nstre am o f an E CW retu rn th rottl e (b utterfly) v al v e.  Su bse quent li cen see inv est iga tion f ound cavitation pitt
inspects for both internal and external corrosion.  The licensee also painted the outside of the


ing , circ um f eren tial pipe crack
ESW pipes to minimize the potential for corrosion.


ing , and pipe-t
Domestically, a potentially similar problem was noted during an NRC inspection at the Point


o-en d f lang e w eld sep arati on in the pi pe.  On Au gust 15 , 20 05, as part of thei r ex tent-o f-con di tio n re v ie w , the li cen see i nsp ecte d Trai n 2 B of the EC W sy stem a nd dete rmin ed that a s imi la r do w nstre am fla n ge h a d a n a p p ro x i ma te l y 3 0 i n ch e s-l o n g b y t h re e i n ch e s-w i d e s e gme n t o f th e a l u mi n u m-bron z e p ip e th at b roke free.
Beach facility.  Like the first foreign event, the licensee for Point Beach did not take appropriate


Train 2B of the E CW sy stem w as dec la red in ope rabl e for th e same reas ons as E CW Trai n 2 A and w as repo rted to th e N RC as a common-c aus e in ope rabi li ty of i nde pen den t trai ns (Li cen see E v ent Re port No. 49 9/20 050 04, Agenc y w id e Do cumen ts A cce ss and M ana gement S y stem (A DA M S) Acc ess io n N o. M L05 263 003 1). The licensee dete
corrective action to resolve a known degraded condition until MIC resulted in an actual failure.


rm ined the cause
Also, like the first foreign event, MIC attack of the EDG endbells represented a common cause


of the dam ag e w as cavitation imping
failure mechanism that could render all of the EDGs inoperable if not properly monitored and


em ent f rom the heavil
resolved.


y throttl ed butte rf ly v al v e. The ro ot c aus e w as the f ai lu re to i nco rpora te re quisi te i nsp ecti on acti v iti es f or E CW pi pi ng i nto stati on programs.On M arch 20 , 20 05, at P oi nt B eac h N ucl ear Pl ant, Un it 1, th e G-0 1 e mergency di ese l genera tor (ED G) be came in ope rabl e d ue to a thro ugh-w al l le ak i n th e e ndb el l of the ED G coo li ng sy stem h e a t e x ch a n ger (In sp e ct i o n R e p o rt 5 0-2 6 6/2 0 0 5-0 1 0 , A D A M S A cc e ss i o n N o. M L 0 5 3 0 0 0 2 3 7).Licensee inspec
ESW systems for U. S. nuclear power plants are generally unique from one plant to another.


tions ident
However, domestic ESW systems typically include piping sections that are buried and not


if ied signif
readily accessible for inspection.  Buried sections of piping can be subject to periodic wetting


icant dam ag e to the endbe
from storms or local flooding conditions.  Exterior protective coatings may also not be fully intact


ll due to m icrobiolog
due to improper installation, age degradation, or maintenance practices.  It is also possible for


ically in duc ed corro si on (M IC).  The li cen see mai nten anc e ru le ev al uati on dete rmin ed that the poo r condit ion of the endbells f
some ESW piping sections to be located in vaults or pipe chases that are subject to periodic


rom pitting caused by
flooding and/or high humidity that can closely mimic the foreign events. Also, at South Texas Project Unit 2, ESW system degradation led to a through-wall leak that


===M IC w as k nown f or near ly ten years, but===
ultimately became an actual common cause failure vulnerability.  Similar cavitation damage was
timely and eff ecti v e c orrec tiv e a cti ons w ere not taken.  Al so, on Ap ril 22 , 20 05, a th rough-w al l serv ic e w a te r (S W) l e a k o cc u rr e d o n t h e G-0 2 E D G h e a t e x ch a n ger a l te rn a te S W s u p p l y l i n e d u e t o M IC.BA CKGRO UND T he ESW syst em (o r its eq uiva len t) f or U. S. co m m er ci al r ea ct or pla nt s is th e as su r ed , sa f et y-rel ated mea ns of transferrin


g sens ib le an d d eca y he at from the
found in two trains of the ESW system at Unit 2.  Proper application of the recommendations of


rea ctor coo la nt s y stem to the ul tima te h eat si nk.  The ES W sy stem i s a ls o re li ed upo n for o ther cri tic al sa f ety functi ons , su ch as prov id in g cool in g w ater f or mo st o f the es sen tia l, safety-rel ated equi pmen t us ed f or miti gatin g pl ant acc id ent and tran si ent con di tio ns, reac tor c ool ant pump se al co ol in g, spen t fuel p o o l c o o l i n g, a n d for d i ss i p a ti n g s e n si b l e a n d r e a ct o r d e ca y h e a t d u ri n g s h u td o w n c o n d i ti o n s.
NRC Generic Letter (GL) 89-13, Service Water System Problems Affecting Safety-Related


IN 200 7-06 P a g e 3 o f 5 Al so, on PW Rs, the safety rel ated au x il ia ry feedw ater sy stems ty pi cal ly rel y on the E SW sy stem as an emer
Equipment, and 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action, likely would


g ency mak eup w ater sourc e f or f eeding the ste am gen erat ors. Plant-s
have prevented this event.


pecif ic prob abi li sti c ri sk asse ssmen ts (P RA s) h av e s how n th at th e l oss of the E SW sy stem may be a si gni fic a n t co n tr i b u to r to t h e p o te n ti a l for a c o re d a ma ge a cc i d e n t. D IS C U S S ION The first
===RELEVANT GENERIC COMMUNICATIONS===
NRC GL 89-13, Service Water System Problems Affecting Safety-Related Equipment, dated


f orei gn ev ent in v ol v ed the f ai lu re to pro perl y pro tect the ex teri or p ip in g surfaces
July 18, 1989, requested specific licensee actions to resolve SW system problems.  In


in the v ic in ity of w el d n eck flanges
particular, this GL recommended that licensees ensure by a routine inspection and


that had be en in stal le d to al lo w pe rson nel ac ces s for i nsp ecti ng the i n si d e E S W s y st e m p i p i n g s u rfac e s.  The u n p ro te ct e d w e l d n e ck jo i n ts w e re s u b je ct t o corro si on.  A ll of the se area s w ere al so sub ject to rou tin e w etti ng of the
maintenance program for open-cycle SW system piping and components that corrosion, erosion protective coating failure, silting, and biofouling cannot degrade the performance of


unp rotec ted ex teri or surface of w el d n eck are as. In add iti on, NR C staff co ncl ude d th at a funda mental sh ortco min g a s s o c i a t e d w i t h t h e fi r s t fo r e i gn e v e n t w a s t h e u t i l i t y's fa i l u r e t o a d e qu a t e l y t r e n d a n d t a ke app ropri ate corre cti v e a cti on f or a know n d egrade d c ond iti on.  D omesti c o pera tin g reacto r pl ants are su bject to Ti tle 10 of the Co de of F ede ral R egu la tio ns (10 CFR) Part 50, Appendix B, Cri teri on XVI, "C orrec tiv e A cti on," w hi ch requi res that prompt and eff ecti v e c orrec tiv e a cti ons be ta ken t o a d d re ss s i gni fic a n t co n d i ti o n s a d v e rs e t o qu a l i ty.  The s eco nd f orei gn ev ent al so in v ol v ed the f ai lu re to pro tect the ex teri or p ip in g surface o
safety related systems supplied by service water.


f the ES W sy stem.  One of the le sso ns le arne d w as to i mpl emen t an i nsp ecti on program th
NRC GL 90-05, Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,
2, and 3 Piping, dated June 15, 1990, provides guidance for Code Class 3 piping.  Two specific


at in spe cts f or b oth in terna l and ex terna l corro si on.  The li cen see al so pai nted the ou tsi de of the ES W pi pes to min imi z e th e p oten tia l f or c orros io n.Do mesti cal ly , a pote nti al ly si mil ar p robl em w as note d d uri ng an N RC i nsp ecti on at th e P oi nt B e a ch fac i l i ty.  L i ke th e fi rs t fore i gn e v e n t, t h e l i ce n se e for P o i n t B e a ch d i d n o t ta ke a p p ro p ri a te co rr e ct i v e a ct i o n t o r e so l v e a kn o w n d e gra d e d c o n d i ti o n u n ti l M IC r e su l te d i n a n a ct u a l fai l u re. Al so, li ke the f irs t forei gn ev ent, M IC attac k of the E DG e ndb el ls rep rese nted a common cau se f ai lu re me cha ni sm tha t co ul d re nde r al l of the ED Gs i nop erab le i f no t pro perl y mon ito red and reso lv ed.E S W s y st e ms for U. S. n u cl e a r p o w e r p l a n ts a re ge n e ra l l y u n i que fro m o n e p l a n t to a n o th e r. Ho w ev er, d omesti c E SW sy stems ty pi cal ly i ncl ude pi pi ng sec tio ns that are buri ed and no t read il y ac ces si bl e for i nsp ecti on.  B uri ed sec tio ns of pi pi ng can be su bject to p eri odi c w etti ng f rom sto rms or lo cal floo di ng con di tio ns.  E x teri or p rotec tiv e c oati ngs may al so not be f ul ly i ntac t due to imp rope r i nsta ll ati on, age d egrada tio n, o r mai nten anc e p racti ces. It is al so pos si bl e for som e ESW piping sect
flaw evaluation approaches, as discussed in Enclosure 1 to the GL, should be considered, namely, the "through-wall flaw" and the "wall thinning" approaches.


ions to be located in v
NRC IN 92-49, Recent Loss Or Severe Degradation Of Service Water Systems, dated July 2,
1992, alerted licensees to several service water related events, including one event that


aults or pipe chases that
resulted in the loss of the ultimate heat sink for a short period of time.


are subj ect to periodic
NRC IN 94-79, Microbiologically Influenced Corrosion Of Emergency Diesel Generator Service


f lo odi ng an d/or hi gh hu mid ity tha t ca n c lo sel y mi mic the f orei gn ev ents.
Water Piping, dated November 23, 1994, alerted licensees that stagnant or intermittent-flow


IN 200 7-06 P a g e 4 o f 5 Al so, at S outh Tex as Pro ject U ni t 2, ES W sy stem d egrada tio n l ed to a thro ugh-w al l le ak that ul tima tel y be came an actu al co mmon c aus e fai lu re v ul nera bi li ty.  S imi la r ca v ita tio n d amage w as f oun d i n tw o tra in s o f the E SW sy stem a t U ni t 2.  P rope r ap pl ic ati on of the reco mmenda tio ns of NR C Generi c L etter (GL) 89-13, "Se rv ic e W ater Sy stem P robl ems A f f ecti ng Sa f ety-Re la ted Eq uipme nt," and 10 CFR Part 50, Appendix B, Criter
conditions, as in the case of emergency diesel service water supply headers, are conducive to


ion XVI , "Cor rec tive A ction," like ly w ould h a v e p re v e n te d t h i s e v e n t.RELEVA NT GENERIC CO
the growth of microorganisms that can accelerate corrosion rates.


MM UNICA T IO NS NR C GL 8 9-13 , "S erv ic e W ater Sy stem P robl ems A f f ecti ng Sa f ety-Re la ted Equi pmen t," da ted Ju l y 1 8 , 1 9 8 9 , re que st e d s p e ci fic l i ce n se e a ct i o n s to r e so l v e S W s y st e m p ro b l e ms.  I n parti cul ar, th is GL reco mmende d th at l ic ens ees en sure by a routi ne in spe cti on and mai nten anc e p rogram f or o pen-cy cl e S W sy stem p ip in g and co mpon ents tha t co rrosi on, eros io n p rotec tiv e c oati ng f ai lu re, s il tin g, and bi ofoul in g cann ot d egrade the pe rf ormanc e o f sa fety r e l a te d s y st e ms s u p p l i e d b y s e rv i ce w a te r.NR C GL 9 0-05 , "Gui dan ce f or P erforming Tempora
NUREG-1275, Volume 3, "Operating Experience Feedback Report - Service Water System


ry N on-C ode R epa ir of ASM E Co de Cl ass 1, 2, and 3 Piping," dat ed June 15, 1990 , pro vi des g uidance f or Code Class 3 piping.
Failures and Degradations in Light Water Reactors," (November 1988) summarizes and


T w o specif ic f la w ev al uati on app roac hes , as di scu sse d i n E ncl osu re 1 to the GL, sh oul d b e c ons id ered , name ly , the "thro ugh-w al l f la w" an d th e "w al l thi nni ng" ap proa che s.NR C IN 92-4 9, "R ece nt L oss Or S ev ere De gradati on Of S erv ic e W ater Sy stems," date d J ul y 2, 199 2, a le rted li cen see s to se v eral se rv ic e w ater rel ated ev ents , i ncl udi ng on e e v ent that resu lte d i n th e l oss of the ul tima te h eat si nk f or a sh ort p eri od of time.NR C IN 94-7 9, "M ic robi ol ogica ll y Influ enc ed Co rrosi on Of E mergency D ie sel Gen erato r S erv ic e W ater Pi pi ng," da ted No v embe r 23 , 19 94, al erted l ic ens ees tha t sta gnant or i ntermi ttent-flow
discusses SW system events from 1980 to early 1987.


co n d i ti o n s, a s i n t h e c a se o f em e rge n cy d i e se l s e rv i ce w a te r su p p l y h e a d e rs , a re c o n d u ci v e t o the grow th o f mi croo rgani sms th at c an acc el erate co rrosi on rates. NU RE G-1275 , V ol ume 3, "Ope rati ng Ex peri enc e F eed bac k Rep ort - Se rv ic e W ater Sy stem Fai lu res and D egrada tio ns in Li ght W ater Re acto rs," (N ov embe r 19 88) summari z es and di scu sse s S W sy stem e v ents from 198 0 to ea rly 19 87.NU RE G-1461 , "R egul atory A nal y si s for the R eso lu tio n o f Gen eri c Is sue 15 3: L oss of Es sen tia l S e rv i ce W a te r i n L W R s," (A u gus t 1 9 9 3) p ro v i d e s a r e v i e w o f i n d u st ry e x p e ri e n ce a n d p l a n t-spe ci f ic P RA s a nd in si ghts rel ated to ES W sy stem v ul nera bi li tie s.
NUREG-1461, "Regulatory Analysis for the Resolution of Generic Issue 153: Loss of Essential


IN 200 7-06 P a g e 5 o f 5 CONTA CT This i nformatio n n oti ce requi res no spe ci f ic ac tio n o r w ritte n re spo nse.  P le ase di rect any q u e s t io n s ab o u t t h is m a t t e r t o t h e t e c h n ic a l c o n t a c t s li s t e d be lo w./TQuay for MCa se/
Service Water in LWRs, (August 1993) provides a review of industry experience and plant- specific PRAs and insights related to ESW system vulnerabilities.


===M ic hae l J. C ase , D ire ctor===
==CONTACT==
Di v is io n o f P ol ic y an d R ul emakin g
This information notice requires no specific action or written response.  Please direct any


Of f ic e o f N ucl ear Re acto r R egul ati onT echnical Contac
questions about this matter to the technical contacts listed below.


ts:
/TQuay for MCase/
Richard A.


Laura, NRR/DIRS
===Michael J. Case, Director===
Division of Policy and Rulemaking


301-415-183 7 E-ma i l: ral 1@n rc.gov
===Office of Nuclear Reactor Regulation===
Technical Contacts: Richard A. Laura, NRR/DIRS


Jam es E. T atum , NRR/DSS
301-415-1837 E-mail: ral1@nrc.gov


301-415-280 5 E-ma i l: jet1@nrc.gov No te: N RC gene ric co mmuni cati ons may be found on the N RC pu bl ic w eb si te,http://w w w.nrc.gov un der El ectro ni c R ead in g Roo m/Doc umen t C ol le cti ons.
James E. Tatum, NRR/DSS


IN 200 7-06 P a g e 5 o f 5 CONTA CT This i nformatio n n oti ce requi res no spe ci f ic ac tio n o r w ritte n re spo nse.  P le ase di rect any q u e s t io n s ab o u t t h is m a t t e r t o t h e t e c h n ic a l c o n t a c t s li s t e d be lo w./TQuay for MCa se/
301-415-2805 E-mail: jet1@nrc.gov


===M ic hae l J. C ase , D ire ctor===
Note: NRC generic communications may be found on the NRC public web site, http://www.nrc.gov under Electronic Reading Room/Document Collections.
Di v is io n o f P ol ic y an d R ul emakin g


Of f ic e o f N ucl ear Re acto r R egul ati onT echnical Contac
==CONTACT==
This information notice requires no specific action or written response.  Please direct any


ts:
questions about this matter to the technical contacts listed below.
Richard A.


Laura, NRR/DIRS
/TQuay for MCase/


301-415-183 7 E-ma i l: ral 1@n rc.gov
===Michael J. Case, Director===
Division of Policy and Rulemaking


Jam es E. T atum , NRR/DSS
===Office of Nuclear Reactor Regulation===
Technical Contacts: Richard A. Laura, NRR/DIRS


301-415-280 5 E-ma i l: jet1@nrc.gov No te: N RC gene ric co mmuni cati ons may be found on the N RC pu bl ic w eb si te,http://w w w.nrc.gov un der El ectro ni c R ead in g Roo m/Doc umen t C ol le cti ons.AD AM S Accessi on N umber:  M L0628 40608 OFFICE
301-415-1837 E-mail: ral1@nrc.gov
 
James E. Tatum, NRR/DSS
 
301-415-2805 E-mail: jet1@nrc.gov
 
Note: NRC generic communications may be found on the NRC public web site, http://www.nrc.gov under Electronic Reading Room/Document Collections.
 
ADAMS Accession Number:  ML062840608 OFFICE


DIRS:IOEB
DIRS:IOEB


===Tech.Edi tor===
Tech.Editor
 
BC:DSS:SBPB
BC:DSS:SBPB


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TL:DIRS:IOEB


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===C B l a d e y===
RLaura
J S e g a l a


MKi n g
CBladey


===C H a we s CMH DA T E===
JSegala
10/18/2 006
 
10/18/2 006
MKing
10/2 3/20 06
 
02/0 1/20 07
CHawes CMH
10/27/2 006 OFFICE
 
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Latest revision as of 05:56, 15 January 2025

Potential Common Cause Vulnerabilities in Essential Service Water Systems
ML062840608
Person / Time
Site: Point Beach, South Texas  NextEra Energy icon.png
Issue date: 02/09/2007
From: Michael Case
NRC/NRR/ADRA/DPR
To:
Richard Laura, NRR/DIRS/IOEB
References
IN-07-006
Download: ML062840608 (6)
v • d • e


UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

February 9, 2007

NRC INFORMATION NOTICE 2007-06: POTENTIAL COMMON CAUSE

VULNERABILITIES IN ESSENTIAL SERVICE

WATER SYSTEMS

ADDRESSEES

All holders of operating licensees for nuclear power reactors, except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert

addressees of the importance of maintaining essential service water (ESW) systems in a

manner that precludes the development of potential common cause failure vulnerabilities due to

piping or heat exchanger degradation. It is expected that recipients will review the information

for applicability to their facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this IN are not NRC requirements; therefore, no specific

action or written response is required.

DESCRIPTION OF CIRCUMSTANCES

There have been two events at foreign operating reactors in which external corrosion of piping

located in vaults has caused a catastrophic loss of one train of the ESW system. These two

events also had common cause failure aspects that were identified as part of the extent-of- condition reviews. The first foreign event occurred at a pressurized-water reactor (PWR)

designed by Westinghouse, that began commercial operation in 1988. On August 25, 2004, while operating at 100 percent power, an ESW system manhole pipe broke circumferentially

prompting a plant shutdown from the total loss of the B train of the ESW system. The event

was of great concern for plant safety because it could have led to a common cause failure in a

system that is the ultimate heat sink for most safety loads. The ESW pipes are buried and use

manholes at certain intervals to allow for inspection and maintenance. The ESW piping is a

BONNA design that uses a steel pipe lined with cement on both sides to prevent corrosion.

The manhole filled with surface water and corroded the exposed carbon steel manhole piping

neck. The break resulted from external corrosion due to improper installation of external

cement pipe coating. The licensee extent-of-condition review found corrosion at two other

ESW manhole necks that also required significant repair.

The second foreign event occurred at a PWR, designed by Framatome, that began commercial

operation in 1988. On December 11, 1998, while operating at 75 percent power, an ESW pipe

ruptured and flooded the piping gallery with sea water. Since the B train of the ESW system

was lost, the operators shutdown the plant. The pipe is composed of prestressed, inner and

outer concrete pipes with embedded strings and steel pipe. A visual inspection of the failed

pipe revealed a 3.3 foot long by 2.8 inches wide through-wall rupture. The prestressed wire

and steel cylinder were found to be severely corroded. The pipe is located in an underground

gallery that has very humid conditions. The licensee determined that condensation got inside a

small crack on the surface of the pipe causing corrosion of the steel wire. The licensee extent- of-condition review identified 16 other pipe spools that were also replaced.

There also have been two events at domestic operating reactor plants that experienced

significant internal degradation of critical ESW components that had the potential for common

cause failures. On June 27, 2005, at the South Texas Project, Unit 2, a three gallons/hour

through-wall leak was identified in Train 2A, essential cooling water (ECW) system piping

flange. The pipe is 30 inches in diameter, composed of an aluminum-bronze, and is located

immediately downstream of an ECW return throttle (butterfly) valve. Subsequent licensee

investigation found cavitation pitting, circumferential pipe cracking, and pipe-to-end flange weld

separation in the pipe. On August 15, 2005, as part of their extent-of-condition review, the

licensee inspected Train 2B of the ECW system and determined that a similar downstream

flange had an approximately 30 inches-long by three inches-wide segment of the aluminum- bronze pipe that broke free. Train 2B of the ECW system was declared inoperable for the

same reasons as ECW Train 2A and was reported to the NRC as a common-cause

inoperability of independent trains (Licensee Event Report No. 499/2005004, Agencywide

Documents Access and Management System (ADAMS) Accession No. ML052630031). The

licensee determined the cause of the damage was cavitation impingement from the heavily

throttled butterfly valve. The root cause was the failure to incorporate requisite inspection

activities for ECW piping into station programs.

On March 20, 2005, at Point Beach Nuclear Plant, Unit 1, the G-01 emergency diesel generator

(EDG) became inoperable due to a through-wall leak in the endbell of the EDG cooling system

heat exchanger (Inspection Report 50-266/2005-010, ADAMS Accession No. ML053000237).

Licensee inspections identified significant damage to the endbell due to microbiologically

induced corrosion (MIC). The licensee maintenance rule evaluation determined that the poor

condition of the endbells from pitting caused by MIC was known for nearly ten years, but timely

and effective corrective actions were not taken. Also, on April 22, 2005, a through-wall service

water (SW) leak occurred on the G-02 EDG heat exchanger alternate SW supply line due to

MIC.

BACKGROUND

The ESW system (or its equivalent) for U. S. commercial reactor plants is the assured, safety- related means of transferring sensible and decay heat from the reactor coolant system to the

ultimate heat sink. The ESW system is also relied upon for other critical safety functions, such

as providing cooling water for most of the essential, safety-related equipment used for

mitigating plant accident and transient conditions, reactor coolant pump seal cooling, spent fuel

pool cooling, and for dissipating sensible and reactor decay heat during shutdown conditions. Also, on PWRs, the safety related auxiliary feedwater systems typically rely on the ESW system

as an emergency makeup water source for feeding the steam generators. Plant-specific

probabilistic risk assessments (PRAs) have shown that the loss of the ESW system may be a

significant contributor to the potential for a core damage accident.

DISCUSSION

The first foreign event involved the failure to properly protect the exterior piping surfaces in the

vicinity of weld neck flanges that had been installed to allow personnel access for inspecting the

inside ESW system piping surfaces. The unprotected weld neck joints were subject to

corrosion. All of these areas were also subject to routine wetting of the unprotected exterior

surface of weld neck areas. In addition, NRC staff concluded that a fundamental shortcoming

associated with the first foreign event was the utilitys failure to adequately trend and take

appropriate corrective action for a known degraded condition. Domestic operating reactor

plants are subject to Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B,

Criterion XVI, Corrective Action, which requires that prompt and effective corrective actions be

taken to address significant conditions adverse to quality.

The second foreign event also involved the failure to protect the exterior piping surface of the

ESW system. One of the lessons learned was to implement an inspection program that

inspects for both internal and external corrosion. The licensee also painted the outside of the

ESW pipes to minimize the potential for corrosion.

Domestically, a potentially similar problem was noted during an NRC inspection at the Point

Beach facility. Like the first foreign event, the licensee for Point Beach did not take appropriate

corrective action to resolve a known degraded condition until MIC resulted in an actual failure.

Also, like the first foreign event, MIC attack of the EDG endbells represented a common cause

failure mechanism that could render all of the EDGs inoperable if not properly monitored and

resolved.

ESW systems for U. S. nuclear power plants are generally unique from one plant to another.

However, domestic ESW systems typically include piping sections that are buried and not

readily accessible for inspection. Buried sections of piping can be subject to periodic wetting

from storms or local flooding conditions. Exterior protective coatings may also not be fully intact

due to improper installation, age degradation, or maintenance practices. It is also possible for

some ESW piping sections to be located in vaults or pipe chases that are subject to periodic

flooding and/or high humidity that can closely mimic the foreign events. Also, at South Texas Project Unit 2, ESW system degradation led to a through-wall leak that

ultimately became an actual common cause failure vulnerability. Similar cavitation damage was

found in two trains of the ESW system at Unit 2. Proper application of the recommendations of

NRC Generic Letter (GL) 89-13, Service Water System Problems Affecting Safety-Related

Equipment, and 10 CFR Part 50, Appendix B, Criterion XVI, Corrective Action, likely would

have prevented this event.

RELEVANT GENERIC COMMUNICATIONS

NRC GL 89-13, Service Water System Problems Affecting Safety-Related Equipment, dated

July 18, 1989, requested specific licensee actions to resolve SW system problems. In

particular, this GL recommended that licensees ensure by a routine inspection and

maintenance program for open-cycle SW system piping and components that corrosion, erosion protective coating failure, silting, and biofouling cannot degrade the performance of

safety related systems supplied by service water.

NRC GL 90-05, Guidance for Performing Temporary Non-Code Repair of ASME Code Class 1,

2, and 3 Piping, dated June 15, 1990, provides guidance for Code Class 3 piping. Two specific

flaw evaluation approaches, as discussed in Enclosure 1 to the GL, should be considered, namely, the "through-wall flaw" and the "wall thinning" approaches.

NRC IN 92-49, Recent Loss Or Severe Degradation Of Service Water Systems, dated July 2,

1992, alerted licensees to several service water related events, including one event that

resulted in the loss of the ultimate heat sink for a short period of time.

NRC IN 94-79, Microbiologically Influenced Corrosion Of Emergency Diesel Generator Service

Water Piping, dated November 23, 1994, alerted licensees that stagnant or intermittent-flow

conditions, as in the case of emergency diesel service water supply headers, are conducive to

the growth of microorganisms that can accelerate corrosion rates.

NUREG-1275, Volume 3, "Operating Experience Feedback Report - Service Water System

Failures and Degradations in Light Water Reactors," (November 1988) summarizes and

discusses SW system events from 1980 to early 1987.

NUREG-1461, "Regulatory Analysis for the Resolution of Generic Issue 153: Loss of Essential

Service Water in LWRs, (August 1993) provides a review of industry experience and plant- specific PRAs and insights related to ESW system vulnerabilities.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contacts listed below.

/TQuay for MCase/

Michael J. Case, Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Richard A. Laura, NRR/DIRS

301-415-1837 E-mail: ral1@nrc.gov

James E. Tatum, NRR/DSS

301-415-2805 E-mail: jet1@nrc.gov

Note: NRC generic communications may be found on the NRC public web site, http://www.nrc.gov under Electronic Reading Room/Document Collections.

CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contacts listed below.

/TQuay for MCase/

Michael J. Case, Director

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Richard A. Laura, NRR/DIRS

301-415-1837 E-mail: ral1@nrc.gov

James E. Tatum, NRR/DSS

301-415-2805 E-mail: jet1@nrc.gov

Note: NRC generic communications may be found on the NRC public web site, http://www.nrc.gov under Electronic Reading Room/Document Collections.

ADAMS Accession Number: ML062840608 OFFICE

DIRS:IOEB

Tech.Editor

BC:DSS:SBPB

TL:DIRS:IOEB

PGCB:DPR

NAME

RLaura

CBladey

JSegala

MKing

CHawes CMH

DATE

10/18/2006

10/18/2006

10/23/2006

02/01/2007

10/27/2006 OFFICE

PGCB:DPR

IP

BC:ADRA:DPR

D:DPR

NAME

QNguyen

JDunnLee

CJackson

MJCase

DATE

02/02/2007

01/22/2007

02/082007

02/09/2007 OFFICIAL RECORD COPY


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