ML17349A671

LER 93-002-00:on 930115,small Steam Leak Discovered on Abandoned Pressurizer Spray Valve Bypass Line.Caused by Welders Failing to Ensure Adequate Pullback of Pipe Cap.New Pipe Cap Welded on & Faulted Line removed.W/930205 Ltr

ML17349A671
Person / Time
Site:	Turkey Point
Issue date:	02/05/1993
From:	Mowrey C, Plunkett T FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-93-027, L-93-27, LER-93-002-01, LER-93-2-1, NUDOCS 9302110423
Download: ML17349A671 (6)

Text

ACCELEtu.D DOCUMENT DISTRIBUTION SYSTEM REGULATORY INFORMATION DISTRIBUTlON SYSTEM (RIDS)

ACCESSION NBR:9302110423 DOC.DATE: 93/02/05 NOTARIZED; NO DOCKET FACIL:50-250 Turkey Point Plant, Unit 3, Florida Power and Light C 05000250 AUTH 'NAME AUTHOR AFFILIATION MOWREY,C.L. Florida Power & Light Co.

PLUNKETT,T.F. Florida Power & Light Co.

RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 93-002-00:on 930115,small steam leak discovered on abandoned pressurizer spray valve bypass line. Caused by welders failing to ensure adequate pullback of pipe cap.New pipe"cap welded on & faulted line removed.W/930205 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:

RECIPIENT COPIES RECIPIENT COPIES .

ID CODE/NAME LTTR ENCL 1D CODE/NAME LTTR ENCL PD2-2 LA 1 1 PD2-2 PD ~ 1 1 RAGHAVAN,L 1 1 INTERNAL: ACNW 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB10 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 NRR/DST/SICBSH3 1 1 NRRJJ3ST/SPLBSD1 1 1 NRR/DST/SRXB SE 1 1 ~EG~E 02 1 1 RES/DSIR/EIB- 1 1 RGN2 FILE 01 1 1

, EXTERNAL: EG&G BRYCE,J.H 2 2 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHYiG A~ 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 NOTE TO ALL"RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTEI CONTACT THE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 504-2065) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEEDI FULL TEXT CONVERSION REQUIRED

.TOTAL NUMBER OF COPIES REQUIRED: LTTR 29 ENCL 29

P.O. Box 029100. Miami, FL, 33102 9100 FEB O 5 Eq3 L-93-027 10 CFR 50 73

~

U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Unit 3 Docket No. 50-250 Reportable Event: 93-002-00 Reactor Coolant S stem Pressure Boundar Leaka e.

Technical S ecification Re ired Shutdown The attached Licensee Event Report 250/93-002-00 is be'ng provided in accordance with 10 CFR 50.73 (a) (2) (i) (A) .

. If there are any questions, please contact us.

Very truly yours,

~-yy/ (.;., /r; T. F. Plunkett Vice President Turkey Point Nuclear TFP/CLM/cm enclosure cc: Stewart D. Ebneter, Regional Administrator, Region II, USNRC Ross C; Butcher, Senior Resident Inspector, USNRC, Turkey Point Plant 10006O-9302110423 930205 PDR ADOCK 05000250 PDR 8

LICENSEE EVENT REPORT (LER)

FACII ITY NAME (1) DOCKET NUMBER (2) PAGE (3)

TURKEY POINT UNIT 3 05000250 1 4 TITLE (4) REACTOR COOLANT SYSTEM PRESSURE BOUNDARY LEAKAGE; TECHN CAL I SPECIFICATION REQUIRED SHUTDOWN EVEhT DATE {5) LER NUMBER(6) RPT DATE {7) OTHER FACILITIES INVOLVED {8)

YR YR SEQ Rt MON DAY YR FACII ITY NAMES DOCKET ( {S) 01 15 93 93 002 00 02 05 93 OPERATING MODE {S) 10 CFR 50.73 a 2 i A POHER LEVEL (10) 100 LICENSEE CONTACT FOR THIS LER (12)

C. L. Mowrey, Licensing OEF Engineer/Analyst TELEPHONE NUMBER

,305-246-6204 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT {13)

CAUSE SYSTEM COMPONENT MANUFACTURER NPRDS2 CAUSE SYSTEM MANUFACTURER NPRDS2 COMPONENT AB PSF X999 SUPPLEMENTAL REPORT EXPECTED {14) 'NO lH YES 0 EXPECTED SUBMISSION MONTH DAY YEAR DATE {15)

{If yee, complete EXPECTED SUBMISSION DATE)

ABSTRACT {16)

On January 15, 1993, Turkey Point Unit 3 was in Mode 1 at 100 percent power. At about 1432, a small steam leak was discovered on an abandoned pressurizer spray valve bypass line. The leak emanated from a socket weld connecting a pipe cap to'he pipe nipple. An Unusual Event was declared for pressure boundary leakage. The Unusual Event was terminated when the unit entered Mode 5.

Increases in Containment radioactivity had been occurring since late December, 1992, but with no measurable change in leakage.

The cause of the leak appears to be personnel error in that welders did not ensure adequate pullback of the pipe cap when 1985. The inadequate pullback caused excessive local stress, which it was installed in resulted in stress corrosion cracking of the fillet weld.

As corrective action, the faulted line was removed and a new pipe cap welde'd one The abandoned spray valve bypass line on Unit 4 will be inspected and/or replaced during the next refueling outage.

LICENSE EVENT REPORT (LER) TEXT ONTINUATXON FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 3 05000250 93-002-00 '02 OF 04 I. DESCRIPTION OF THE EVENT On January 15, 1993, Turkey Point Unit 3 was in Mode 1 at 100 percent power.

At about 1432', a small steam leak was discovered on an abandoned pressurizer spray valve [AB; pzr, pcv] bypass line, between the previous "A" spray valve body and the pressurizer spray nozzle [AB: pzr, nzl].

Indications of increasing activity in the containment atmosphere had been occurring since late December, 1992. Containment Particulate Monitor R-ll

[IK; mon] and Containment Gas Monitor R-12 [IK: mon] had elevated readings and occasional'pikes, which seemed to be related to operation of the pressurizer spray valves'. RCS leakage showed no measurable increase, and containment entries made prior to January 15, 1993, for leak inspections uncovered no leakage. I'n January 15, 1993, at about 1135, the leak was discover'ed in the vicinity of the abandoned spray valve bodies. Because of the location of the leakage (inside the pressurizer cubicle), exact determination of the leak point was very difficult. At about 1432, the leak was determined to be on the abandoned spray valve bypass line.'ased on its location the leak was declared to be RCS pressure boundary leakage.

Technical Specification 3.4.6.2a requires that for any'ressure boundary leakage, the plant must be in HOT STANDBY (Mode 3) within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN (Mode 5) within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />. Since the leak could not be isolated, it was declared to be pressure boundary leakage, resulting in the Notification of an Unusual Event (NOUE). The NRCOC was notified of the NOUE at 1450 'he unit entered Mode 3 at 1755, on January 15, entered Mode 5 at 1815 on January 16, 1993, and downgraded the Unusual Event to a non-emergency event.

The leak emanated from a pipe cap to nipple socket weld. There was a visually discernable 1/4" linear indication within the weld metal.

Subsequent liquid penetrant examination further confirmed the magnitude of the flaw via heavy bleed-through along an approximate 1/2" circumferential area.

II. CAUSE OF THE EVENT Immediate Cause The immediate cause of the Unusual Event was a leak through the fillet weld between the pipe nipple and the pipe cap. Since the leak could not be isolated, it was considered pressure boundary leakage.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILITY NAME DOCKET NUMBER - LER NUMBER PAGE NO.

-TURKEY POINT UNIT 3 05000250 93-002-00 03 OF 04 Interme'diate Cause The intermediate cause of the leak was stress corrosion cracking (SCC) of the fillet weld. In order for SCC to occur, the critical amount of stress, environment, and susceptible material all need to be present.

Examination showed inadequate "pullback" between the pipe and the cap. The lack of pullback can cause high localized stresses which increase the chances and effects of stress corrosion cracking. The direction and orientation of the failure, which corresponds to the shear plane through the thioat of the fillet weld, supports the presence of stresses induced from inadequate pullback.

Although contaminants are controlled to low levels in the RCS, the stagnant conditions resulting from this particular piping configuration could have led to higher localized concentrations of contaminants.

The high stress and stagnant condit'ions, combined with the susceptible material (316 stainless steel) eventually resulted in leak path development through the throat of the fillet weld.

Root Cause The root cause of the leak appears to be personnel error in that non-licensed contract personnel did not ensure adequate pullback of the pipe cap when it was installed, as part of a plant modification in 1985. A review of the configuration of the capped bypass lines shows that while this cap was installed vertically (cap "hanging down"), the other caps were installed horizontally.

While welding the vertical cap, it may have been difficult to hold it in the precise vertical location to get the required pullback. It would be easier to hold the cap bottomed against the pipe. The close proximity of the integral attachment suppozt in the field and other spatial limitations made the weld fitup and access difficult. In the other two lines, the horizontal orientation would allow for better positioning and the required" pullback.

ZZZ . ANALYSIS OF THE EVENT The leak was discovered as a result of inspections conducted as a result of increased readings on the Containment Atmosphere Gaseous and Particulate Radioactivity Monitors. At no time did the RCS leak rate exceed the Technical Specification Limiting Condition for Operation for unidentified RCS leakage of 1 GPM. RCS leak detection is a recognized function of the containment activity monitors, required by Technical Specification 3.4.6.1.

R-11 and R-12 on Unit 3 are new instruments, installed during the refueling outage completed last December. Their accuracy has been demonstrated to be nearly an order of magnitude better than the instruments they replaced. As a result, they made possible the very early detection of this leak, which was on the order of 2-3 drops per minute when found.

LICENSE EV1 NT REPORT (LER) . TEXT ONTINUATION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO. ~

TURKEY POINT UNIT 3 05000250 93-002-00 04 OF 04 This type of weld defect is not expected to result in catastrophic failure, but may gradually increase if unattended. Nevertheless, had the weld catastrophic failure, the size of the break would have been limited 'uffered to the three-quarter inch diameter of the abandoned bypass line. Schedule 80 piping of three-quarter inch nominal pipe size translates into a break area of 0.376 square inches. This size of break is bounded by the small break Loss Of Coolant Accident analyzed in the Updated Final Safety Analysis

, Report, Section 14.3 '.2, in which the limiting small break size is given as a two inch diameter cold leg break (3. 142 square inch area) .

IV. CORRECTIVE ACTIONS 1 ~ The section of pipe with the failed weld was removed, along with a tee and another pipe cap, and a new pipe cap welded in place.

2. The vertical cap on the abandoned spray valve bypass line on Unit 4 will be inspected for evidence of sufficient pullback, and/or replaced during the next refueling outage.

V. ADDITIONAL INFORMA.TION A similar leak was reported in LER 250-92-014-00. In that event, the leak was through the pipe cap itself, because the pipe cap was an inappropriate material (machined from bar stock rather than forged) in the format [EIIS SYSTEM: function

.'IIS Codes are shown IEEE component identifier, second component function identi'fier (if appropriate)].-