Information Notice 2005-08, Monitoring Vibration to Detect Circumferential Cracking of Reactor Coolant Pump and Reactor Recirculation Pump Shafts

Monitoring Vibration to Detect Circumferential Cracking of Reactor Coolant Pump and Reactor Recirculation Pump Shafts

ML050730093
Person / Time
Site:	Hope Creek
Issue date:	04/05/2005
From:	Hiland P NRC/NRR/DIPM/IROB
To:
Telson, R - NRR/DIPM/IROB - 415-2256
References
TAC MC6269 IN-05-008
Download: ML050730093 (5)

UNITED STATES

NUCLE AR RE GULATOR Y COM MISS ION OFFICE OF NUC LEAR REAC TOR REGU LATION WASHINGTON, D.C. 20555 April 5, 20

05 NRC INFORM

ATION NOTICE 2005-08:

MONITORING VIBRAT

ION TO DETECT

CIRCU MFER ENTIAL CRAC KING OF REAC TOR COOLAN T PUM P AND REAC TOR REC IRCU LATI ON P UM P SH AFTS

ADDRESSEES

All holders

of oper ating lic enses f or nuclea r power rea

ctors , except t

hose who have

permanently

ceased operati

ons and hav

e certified that fuel

has been p

ermanently re

moved from the react

or vessel.

PURPOSE

The U.S. Nucl ear Re gulato ry Co mmissi on (NR C) is issui ng this informa tion n otice (IN) to alert addressees to th

e importance o

f timely detecti

on of circumferential

cracking of reactor cool

ant pump (RCP) and

reactor recircul

ation pump (RR

P) shafts to minimi

ze the li kelihood of

consequ entia l sha ft failur es. It is expe

cted that recip

ients wi ll revi ew the i nformation for applic

ability to their facil

ities and consi der ac tions , as ap propri ate, to avoi d simi lar pr oblems. How ever, the su ggestion s in t his IN are no t NRC require ments; t herefore , no sp ecific actio n or w ritten respo nse i s requi red. DESC RIPT ION OF CIRCUMSTANCES

General Elec

tric (GE) Nucle

ar Service

s Information Letter (S

IL) 459-S2, iss

ued October 21, 1991, informed GE b

oiling w ater reactor (BWR) owners of sha

ft cracking in RRPs.

The root cause was d etermi ned to be fati gue in itiat ed by therma l stre sses th at, comb ined with mechanical s

tresses, caused

cracks to propagate. GE

recommended counte

rmeasures includin g shaft vibration

monitoring, ins

pection of shafts w

ith greater than 8

0,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of

service, an

d measures to red

uce mechanica

l and thermal

stresses.

At H ope Cre ek, RRP s ha d a ccu mul ate d o ve r 13 0,0 00 hou rs o f se rv ice wi tho ut p ump sha ft inspections. The licens

ee had opera

ted the B RR

P for several

refueling cycl

es with vibration levels approaching v

endor limits. During this

time, the lic

ensee also

identified fail

ed and degraded RRP seals and concluded that the mos

t likely causes of the failed and degr

aded RRP seals were a pos sibl e bow in th e pump shaft an d low reli abil ity o f the sea l purge syste m.ML050730093 IN 2005-08 Pag e 2 of 4 The licensee's decision to restart f

ollowing the fall 2004 refueling outag

e without correcting this

con di tio n l ed to h ei ght ene d p ubl ic in ter est an d p rom pte d a cl ose NR C re vi ew. Th e st aff evaluated site-specific

technical d

etails, rela

ted domestic an

d internation

al operatin

g expe rienc e, and the gen eric s afety a spects of vi bratio n-rela ted sh aft and seal failur e. Circumferential c

racking of RCP and

RRP shafts had

previousl y been rep

orted at seve

ral facilities i

ncluding Sequo

yah, Palo Verde, St. Luc

ie, and Grand

Gulf. In additio

n, reactor

coolant pump

shafts at Crystal

River se parated complete

ly durin g operation on

two occasi

ons (see IN 86-19 and IN 89-15).The staff evaluated the licensee's determination that the Hope Creek

unit could be safely

returned to pow

er with th

e existi ng pump shaft and the

interim compensa

tory measures

imple mented to prov ide re asona ble a ssuran ce tha t a sha ft failur e coul d be d etecte d in i ts incipien t stage and operato

rs would take prompt action to

prevent the

occurrence of a p

otential shaft and seal f

ailure. The licens

ee comm itted t o (1) rep lace the B p

ump shaf t at the next outage of sufficient durati

on and to (2)

establish a

comprehensiv

e program of enhanced

continuous v

ibration moni

toring to ensure

timely dete

ction of circumferentia

l crack propagation

with proce

duralize d contingency

actions for pla

nt operators to a

ct promptly a

t specified

administrativ

e vibrati on limits to

reduce pump sp

eed or shut the

pump down

completely. The same monitoring reg

ime was implemented for the A RRP.

The Hope Creek l

icensee impl

emented a program to c

ontinuously

monitor the sy

nchronous speed (1X) vi

bration ampli

tude, two ti

mes synchrono

us speed (2X) v

ibration ampl

itude, 1X phase angle, a

nd 2X phase an

gle. These parameters

provide a more sensiti

ve leadi ng indi cator o f circum ferenti al cra ck ini tiati on and propa gation givi ng the o perato rs eno ugh time to respond. Al

arm limits w

ere establis

hed using the

ASME OM standard, "Reac

tor Coolant a

nd Recir culat ion P ump Co nditi on M onito ring." GE SIL 45 9 indicat es that all Byron Jac

kson (now Flowserve)

RRP shaf ts inspe cted have show n some degree of therma lly indu ced cra cking. Th

e cracki ng occu rs nea r the p ump thermal barrier

where the

cold seal

purge system w

ater mixes w

ith the hot rea

ctor coolant

water. The cra

cks initiate a

s axial cracks in the p

ump shaft. Axi

al cracks are genera

lly ben ign, grow slow ly, and d o not affect the operati

on of the pump. H

owever, given sufficient me

chanical loads, the ax

ial cracks can

change directi

on and propa

gate circumferentiall

y. The time i

t takes to tr ansi tion from s low-grow ing a xia l cr acks to mo re ra pid ly grow ing c ircu mfere ntia l cr acks depen ds on the magn itude of the me

chani cal l oads o n the p ump sha ft. It cou

ld take year s. On the oth er hand, circum fere ntial sha ft cr acking can propa

gate r apidly and, if not de

tected early, may re sult i n compl ete se veran ce of the shaft.Circumferential s

haft cracking or shaft separati

on could res

ult in pump

damage and

degra dati on o r fai lure of th e pu mp se al p acka ge re sul ting in l eaka ge of r eact or co ola nt th rough clearances a

round the uppe

r portion of the p

ump shaft. Howe

ver, at Cry

stal Riv er - where

the only tw o instances

of shaft failure occurred

at domestic nuc

lear pow er plants - the

re was no evidence of seal degradation. A loss-of-coolant accident can occur if leak

age through the seals

of a RRP or RC

P exceeds the capacity

of the normal makeup

systems. Thus ci

rcumferential

shaft cra cking th at lea ds to s haft or s eal fai lure i s a safe ty co ncern.

IN 2005-08

Pag e 3 of 4 As noted abo

ve, vib ration-monitori

ng systems are a

vailabl e to detect ci

rcumferential cracking o

f pump sh afts. As circu mferenti al cra cks prop agate, t he sti ffness of th

e pump shaft ch anges. The se c han ges are de tec tab le thr oug h ch ang es i n th e p ump vi bra tio n si gna tur e p rio r to sha ft failure. Altho

ugh overall

pump vibra

tion limits

are necessary

for assessing gaps an

d clearances

in the pump, th

ey are not

the most appropri

ate indicato

r of shaft cracking. Mon

itoring the 1X

and 2X steady-state vectors (1

X and 2X amplitu

des and phas

e angles) prov

ides a better

indi catio n of cha nges in shaft i ntegrit y res ultin g from cir

cumferen tial crack pr opagati on. Licensees sh

ould be al

ert to the possi

bility of circumferential RC

P or RRP sh

aft cracking and

shoul d eva luate the i nformati on in this IN and determ ine w hat ac tions , if any , are p rudent to provide early detection of circumf

erential shaft crack

ing and prevent failure of RRP or RCP

shafts and shaft seal

s.GENERIC IMPLICATIONS

A significant nu

mber (about hal

f) of the BWR RRP pump shafts currently

in servi ce are older

and have more hours of operati

on than those

at Hope Creek a

nd many hav

e not been

inspected as

recommended in

GE SIL 459-S2

.About a hal

f-dozen BWR RRPs were

identified as

having hi

gher vibratio

n level s than Hope

Creek. Such is

sues woul d not necessa

rily be reported to the N

RC. The staff contacted th

ree BWR licensees whos

e plants had

been reported

to have hi

gher vibratio

n level s than Hope

Creek. The three pl

ants includ

ed Susquehanna

Units 1 an

d 2, Peach B

ottom Units 2 a

nd 3, and Br owns Ferry Units 2 and 3. The staff dis

cussed wit h each lice nsee h ow i t monit ors pu mp vibr ation , the v ibrati on acc eptanc e crit eria u sed, a nd w hy th e curre nt vi bratio n lev els a re acceptable. These licensees indicated that

they have either replaced their pump shafts (o

r will in the near

future) or are taking steps

to monitor RRP

vibratio n and hav e establish

ed accept ance c riteri a to de tect an omalou s beha vior.Operati ng exp erien ce sugge sts tha t press uriz ed w ater re actor (PWR) RCPs a

re not immune to vibration-related shaft and

seal failure

concerns simi

lar to BWR RRP concerns.

PWR RCP seal

failure can be

more safety signi

ficant than BWR RRP seal

failure because (1) PWR reactor

coolant sy

stems operate at h

igher pressures, i

ncreasing the di

fferential pressure ac

ross the pump seals an

d (2) PWR RCPs, unlike B

WR RRPs, typically

can not be

isolated from the

reacto r cool ant sy stem fol low ing a s eal fai lure. In add ition , whi le a n umber o f BWR RRP sha

fts have cracked, s

everal PWR RCP shafts ha

ve complete

ly sev ered.

IN 2005-08 Pag e 4 of 4

CONTACT

This information no

tice requires no

specific acti

on or wri tten response.

Please di rect any questions about

this matter to the

technical c

ontact(s) listed

below or the appropri

ate Office of

Nucle ar Rea ctor Re gulati on (NR R) pro ject man ager./RA/Patrick L. Hil

and, Chief

Reactor Operatio

ns Branch Divisi on of Inspection

Program Management

Office of Nuclear Reacto

r Regulation

Technical Co

ntacts: W illiam Poertner, NRR

Ross Telson, NRR

(301) 415-5787

(301) 415-2256 E-mail wkp@nrc.gov

E-mail rdt@nrc.gov

Note: NRC gene

ric communicati

ons may be

found on the NR

C public Web site, http://www.nrc.gov , under Elec

tronic Readi

ng Room/Document Co

llections.

IN 2005-08 Pag e 4 of 4

CONTACT

This information no

tice requires no

specific acti

on or wri tten response.

Please di rect any questions about

this matter to the

technical c

ontact(s) listed

below or the appropri

ate Office of

Nucle ar Rea ctor Re gulati on (NR R) pro ject man ager./RA/Patrick L. Hil

and, Chief

Reactor Operatio

ns Branch Divisi on of Inspection

Program Management

Office of Nuclear Reacto

r Regulation

Technical Co

ntacts: W illiam Poertner, NRR

Ross Telson, NRR

(301) 415-5787

(301) 415-2256 E-mail wkp@nrc.gov

E-mail rdt@nrc.gov

Note: NRC gene

ric communicati

ons may be

found on the NR

C public Web site, http://www.nrc.gov , under Elec

tronic Readi

ng Room/Document Co

llections.

DISTRIB UTION: ADAMS IN File ADAMS ACCESSION N

UMBER: ML05073 0093 OFFICE OES:IROB:DIPM

TECH EDITOR

EMEB:DE SC:CI&T:EMEB

C:EMEB NAME RTelson PKleene WPoertner DTerao Eimbro DATE 03/17/2005

03/22/2005

03/17/2005

03/18/2005

03/18/2005 OFFICE D:DE LPD1:DLPM A:SC:OES:IROB:DIPM

C:IROB:DIPM

NAME MMay field DSCollins (E-m ail)EJBenner PLHiland DATE 03/20/2005

04/05/2005

04/05/2005

04/05/2005 OFFICIAL RECORD COPY