ML17284A755

LER 98-015-00:on 980808,discovered Reactor Coolant Pressure Boundary Leak During Shutdown Conditions.Caused by Leakage from Socket Weld (Fwb 63) on Elbow Connection.Failed Piping Connection Was Replaced.With 980902 Ltr

ML17284A755
Person / Time
Site:	Columbia
Issue date:	09/02/1998
From:	Bemis P, Pfitzer B WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GO2-98-159, LER-98-015, LER-98-15, NUDOCS 9809150046
Download: ML17284A755 (9)

Text

y CATEGORY ly REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9809150046 DOC.DATE: 98/09/02 NOTARIZED- NO DOCKET FACIE:50-397 WPPSS Nuclear Project, Unit 2, Washington Public Powe 05000397 AUTH. NAME AUTHOR AFFILIATION PFXTZER,B. Washington Public Power Supply System BEMIS,P.R. Washington Public Power Supply System RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 98-015-00:on 980808,discovered reactor coolant pressure boundary leak during shutdown conditions. Caused by leakage from socket weld (FWB 63) on elbow connection. Failed piping connection was replaced. With 980902 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE: E TXTLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECXPIENT COPIES 0

ID CODE/NAME LTTR ENCL ZD CODE/NAME LTTR ENCL PD4-2 PD 1 1 POSLUSNY,C 1 1 INTERNAL: ACRS 1 1 AEOD 2 2 AEOD/SPD/RRAB 1 1 E CENTER 1 1 NRR/DE/ECGB 1 1 NRR DE EELB 1 1 NRR/DE/EMEB 1 .

1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOHB 1 1 NRR/DRCH/HQMB 1 1 NRR/DRPM/PECB 1 1 NRR/DSSA/SPLB 1 1 RES/DET/EIB 1 1 RGN4 FILE 01 1 1 .D EXTERNAL: L ST LOBBY WARD 1 1 LITCO BRYCE,J H 1 1 0 NOAC POORE,W. 1 .1 NOAC QUEENER,DS 1 1 NRC PDR 1 1 NUDOCS FULL TXT 1 1 N

NOTE TO ALL nRIDSn RECIPIENTS PLEASE HELP US TO REDUCE WASTE. TO HAVE YOUR NAME OR ORGANIZATION REMOVED FROM DISTRIBUTION LISTS OR REDUCE THE NUMBER OF COPIES RECEIVED BY YOU OR YOUR ORGANIZATION, CONTACT THE DOCUMENT CONTROL DESK (DCD) ON EXTENSION 41S-2083 FULL'TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUXRED: LTTR 23 ENCL 23

WASH I YGTOXi'UBLICPOWER SUPPLY SYSTEM P.O. l3ox 968 ~ Richlrwtrl, Washit stot t 99352-0968 September 2, 1998 G02-98-159 Docket No. 50-397 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Gentlemen:

Subject:

NUCLEAR PLANT WNP-2, OPERATING LICENSE NPF-21, LICENSEE EVERT REPORT NO. 98-015-00 Transmitted herewith is Licensee Event Report No. 98-015-00 for WNP-2. This report is submitted pursuant to 10 CFR 50.73 and discusses the items of reportability, corrective action taken, and action to preclude recurrence.

Should you have any questions or desire additional information regarding this matter, please call me or Mr. Paul Inserra at (509) 377-4147.

Respectfully, R Bemis Vice President, Nuclear Operations Mail Drop PE23 Enclosure cc: EW Merschoff, NRC RIV NRC Sr. Resident Inspector, MD927N (2)

DF Kirsch, NRC RIV, WCFO INPO Records Center - Atlanta, GA C Poslusny, Jr., NRR DL Williams, BPA, MD1399 PD Robinson, Winston & Strawn 9809i50046 980902 PDR ADOCK 05000397 S PDR

LICENSEE EVENT REPORT (LZR)

FACILITY NANE (1) DOCKET NUMBER (2) PAGE (3)

Washin ton Nuclear Plant - Unit 2 50-397 1 OF 4 TITLE (4)

Discove of Reactor Coolant Pressure Bound Leak Durin Shutdown Conditions EVENT DATE (5) LER NUHBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (8)

DAY SEQUENTIAL REV. DAY FACILHYNAME DOCKEINUMBER NUMBER NUMBER FACIUIYNAME DOCKETNUMBER 08 08 98 98 015 00 09 02 98 N/A OPERATiNG NODS THIS REPORT IS SUBHITTED PURSUANT TO THE REQUIREHENTS OF 10 CPR 5: (Check one or rsore) (11) 20.402(h) 20.405(c) 50.73(a)(2)(iv) 73.71(b) 20.405(a)(1)(I) 50.36(c)(1) 50.73(a) (2)(v) 73.71(c) 20.405(a)(1)(il) 50.36(c)(2) 50.73(a)(2)(vii) OTHER 0

20.405(a)(1)(iii) 50.73(a)(2) Qi 50.73(a)(2)(viii)(A) 20.405(a)(1)(iv) 50.73(a)(2)(i() 50.73(a)(2)(vile(B) 20.405(a)(1)(v) 50.73(a)(2) (ill) 50.73(a) (2)(x)

LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMBER (Inc(ude Area Code)

Bill Pfitzer, Licensing Engineer 509-377-2419 CONPLETE ONE LINE FOR EACH COHPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE COMPONENT MNAIvxcIvsra REPORTABLE CAUSE svs' COMPONENT. MANUFACTURER REPORTABLE

'.@'.$h O~,q 1 TO EP(X TO EP(X SUPPLEHENTAL REPORT EXPECTED (14) EXPECTED MONTH DAY YEAR YES NO,

( s coIII le(ed EXPECTED SUBMISSION DATE ABSTRACT:

In July of 1998, after plant restart from a forced outage, WNP-2 experienced indications of reactor coolant system (RCS) leakage inside primary containment. These indications were the presence of unidentified leakage as indicated by drywell floor drain sump flow, and elevated gaseous radiation levels inside primary containment.

The unidentified leakage peaked at 0.56 gpm during plant shutdown, well within the Technical Specification 3.4.5.b limit of 5.0 gpm.

A subsequent plant shutdown afforded the opportunity on August 8, 1998 for personnel to enter the drywell to inspect the source of the leakage. The inspection was performed at an RCS pressure of 200 psig and revealed the leakage to be from socket weld (FWB 63) on an elbow connection in a 3/4 inch instrument sensing line (PI(l)-4S-X62d) attached to reactor recirculation (RRC) loop B piping.

The failed piping connection has been replaced. A metallurgical evaluation of the failed piping connection confirmed that the failure was attributable to fatigue.

Small leaks of this magnitude (0.56 gpm) are bounded by the small 'piping break accident analysis and the instrument line break accident analysis of the WNP-2 Final Safety Analysis Report. Also, leakage caused by fatigue cracking failure is generally manifested by a slow increase in leakage which is detectable and trendable. Therefore, the safety significance of this event is considered minimal.

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LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NANE ( I) DOCKET NUNBER I2) LER NUMBER I6) PAGE f3)

SEQUENTIAL REVISION NJNBER NUNBBs Washington Nuclear Plant - Unit 2 50-397 98 015 00 2 OF 4 TEXT (If more space is required, use additional copies of NRC Form 366A) ()7)

Event Descri tion During the month of July, 1998, after plant restart from a forced outage, WNP-2 experienced indications of reactor coolant system (RCS) leakage inside primary containment. These indications were the presence of unidentified leakage as indicated by drywell floor drain sump flow, and elevated gaseous radiation levels inside primary containment. The unidentified leakage peaked at 0.56 gpm during plant shutdown, well within the Technical Specification 3.4.5.b limit of 5.0 gpm.

A subsequent plant shutdown afforded the opportunity on August 8, 1998 for personnel to enter the drywell to inspect the source of the leakage. The inspection was performed at an RCS pressure of 200 psig and revealed the leakage to be from socket weld (FWB 63) on an elbow connection in a 3/4 inch instrument sensing line

'(PI(1)-4S-X62d) attached to reactor recirculation (RRC)[AD] loop B piping.

.An event notification call was made to the NRC Headquarters Operations Officer at 1216 PDST on August 8, 1998 per the requirements of 10 CFR 50.72(b)(2)(i). Event number 34620.

mmedi rr ti eAci n A problem evaluation request was initiated for the condition and repair activities for the leak were initiated.

Industry experience has shown that the main causes of small bore piping failures at socket weld joints are fatigue and intergranular stress corrosion cracking (IGSCC). INPO Operations and Maintenance Report (OkMR) 424 indicates that approximately 80% of these failures are due to fatigue, and 20% are due to IGSCC. Most of these failures were in cantilevered lines (unsupported test, vent or drain connections), versus complex lines (continuous spans), such as the subject instrument line.

Fatigue cracking resulting in leakage can be induced by vibration stresses or thermal stresses. The initial flaw is introduced either by fatigue or a material defect, and crack growth occurs due to cyclic stresses from vibration or thermal cycling. These cyclic stresses can propagate a crack through the piping wall, resulting in leakage. A flaw can also be introduced in small bore piping by stresses generated from events such as being stepped on or used for climbing support.

Also considered was the possible effect of the removal in 1994 of a hanger support from the subject line; a modification which increased the piping flexibility. It should be noted that removal of the hanger was performed to lower thermal stresses on the instrument line socket weld attachment to the RRC piping. However, the hanger removal made the line more susceptible to loads potentially induced during maintenance activities.

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LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION FACILITY NAME I '- ) DOCKET NUMBER (2) LER NUMBER I6) PAGE I3)

YEAR SEQUENTIAL REVIS )OH NUMBER MNB SR Washington Nuclear Plant - Unit 2 50-397 98 015 00 4 OF 4.

TEXT (If more space Is required, use additional copies of NRC Form 366A) (17)

A warning concerning improper use of small bore piping for footholds, handholds and shielding support will be placed in the outage handbook.

Asse sment of Safet on ence Small leaks, such as the leakage caused by the subject piping failure (0.56 gpm), are bounded by the small piping break accident analysis and the instrument line break accident analysis of the WNP-2 Final Safety Analysis Report. Also, leakage caused by fatigue cracking failure is generally manifested by a slow increase in leakage which is detectable and, as in this case, can be trended by control room personnel and verified to be less than the Technical Specification 3.4.5 limit for unidentified leakage of less than 5.0 gpm. Therefore, the safety significance of this event is considered minimal.

imilar Even Small bore piping connection failures, both socket weld and compression fitting types, have been an industry concern and continue to occur frequently as discussed in INPO's OSMR 424 referenced above.

A review of the WNP-2 repair activities for failed socket welds indicates that the majority of failures are in cantilevered lines, and are due to fatigue failure with crack propagation occurring from the outside to the inside of the pipe at the toe of the weld. Only three complex (instrument) line cracks or leaks have been documented at WNP-2 including the failure documented in this report. Of the two previously documented complex instrument line failures, one was attributed to IGSCC initiated/fatigue failure and the other was a fabrication defect/fatigue failure.

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