ML17352A518

LER 94-002-00:on 940310,personnel Discovered Indication of Boric Acid on a Flux Mapper Guide Tube.Caused by Tgscc. Plant Shut Down & Leaking Guide Tube repaired.W/940404 Ltr

ML17352A518
Person / Time
Site:	Turkey Point
Issue date:	04/01/1994
From:	Knorr J, Plunkett T FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-94-078, L-94-78, LER-94-002-01, LER-94-2-1, NUDOCS 9404110261
Download: ML17352A518 (10)

Text

t ACCELERATED DISTRIBUTION DEMONSTPWTION SYSTEM t

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9404110261 DOC.DATE: 94/04/04 NOTARIZED: NO DOCKET FACIL:50-251 Turkey Point Plant, Unit 4, Florida Power and Light C 05000251 AUTH. NAME AUTHOR AFFILIATION KNORR,J.E. Florida Power & Light Co.

PLUNKETT Florida Power & Light Co.

RECIP. NAME RECIPIENT AFFILIATION

SUBJECT:

LER 94-002-00:on 940310,personnel discovered indication of boric acid on a flux mapper guide tube. Cause leak due to D TGSCC.Corrective action:plant shutdown & leaking guide tube was repaired.W/940404 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 D ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-2 PD 1 1 CROTEAU,R 1 1 D INTERNAL: AEOD/DOA 1 1 AEOD/DSP/TPAB ~ 1 1 AEOD/ROAB/DSP 2 2 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DORS/OEAB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR DRIL/RPEB 1 1 NRR/DRSS/PRPB 2 2 ~B SPLB 1 1 NRR/DSSA/SRXB 1 1 G+gJ N 02 1 1 RES/DSIR/EIB 1 1 RGN2 FILE 01 1 1 EXTERNAL EG&G BRYCE i J ~ H 2 2 L ST LOBBY NARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 D

D D

NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACI'HE DOCUMENT CONTROL DESK, ROOM Pl-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

FULL TEXT CONVERSION REQUIRED TOTAL NUMBER OF COPIES REQUIRED: LTTR 27 ENCL 27

FPL APR "4 595 L-94-078 10 CFR 50 '3 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

Re: Turkey Point Unit 4 Docket No. 50-251 Reportable Event: 94-002-00 Plant Shutdown Re uired Due to Reactor Coolant S stem Pressure Boundar Leaka e The attached Licensee Event Report, 251/94-002-00, is being provided in accordance with 10 CFR 50.73(a) (2) (i) (A) .

If there are any questions, please contact us.

Very truly yours, T. F. Plunkett Vice President Turkey Point Plant

'TFP'/JEK/3k enclosure cc: Stewart D., Ebneter, Regional Administrator, Region II, USNRC Thomas P. Johnson, Senior Resident Inspector, USNRC, Turkey Point Plant

", ~ n~q~j 9404110261 940404 PDR ADOCK 05000251 8 ,PDR an FPL Group company

Ih II LICENSEE EVENT REPORT (LER)

FACILITY NAME (1)

DOCKET NUMBER (2) PAGE l3)

TURKEY POINT UNIT 4 05000251 QF 3 TITLE l 4)

PLANT SHUTDOWN REQUIRED DUE TO REACTOR COOLANT SYSTEM PRESSURE BOUNDARY LEAKAGE EVENT DATe (5) LER NUMBERl6) RPT DATE (7) OTHER FACILITIES INV, l8)

MON DAY YR YR SEQ R( DAY YR FACI(,ITY NAMES DOCKET 6 (S) 03 10 002 00 04 01 94 OPERATING MODE (9)

POWER LEVEl (10) 100 10 CFR 50.73 a 2 i A LICENSEE CONTACT FOR THIS LER (12)

TELEPHONE NUMBER J. E. Knorr, Licensing Specialist 305-246-6757 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13)

CAUSE SYSTEM COMPONENT MANUFACTURER NPRDS7 CAUSE SYSTEM COMPONENT MANUFACTURER NPRDS7 D IG TBG W120 SUPPLEMENTAL REPORT EXPECTED (14) NO 8 Yes Cl EXPECTED SUBMISSION MONTH DAY YEAR DATe l15)

(1f yes, coetPlete EXPECTED SUBMISSION DATE)

ABSTRACT (16)

On March 10, 1994, with Unit 4 at 100% rated power, Florida Power and Light Company personnel discovered an indication of boric acid on a flux mapper guide tube. The location of the indication was just above the seal table.

At approximately 0600 EST March 10, 1994, an Unusual Event was declared in accordance with EPIP 20101, due to a Technical Specification required shutdown. Required NRC and State notifications were completed.

The small indication found on the guide tube was due to outside diameter chloride induced transgranular stress corrosion cracking.

The affected section of guide tube and associated fitting adapter was removed and a new fitting adapter installed on the newly prepared guide tube end.

The reactor coolant system was pressure tested and Unit 4 was returned to service This Technical Specification required nuclear plant shutdown is being reported in accordance with 10 CFR 50.73(a) (2) (i) (A) .

LICENSEE ENT REPORT (LER) TEXT VZZNUATZON FACILZTY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 4 05000251 94-002-00 02 OF 03 X. DESCRIPTION OF THE EVENT On March 10, 1994, with Unit 4 at 100% rated power, during an at-power in-containment inspection, performed every 6 weeks, Florida Power and Light Company personnel discovered a minute indication of boric acid on a flux mapper guide tube (thimble N-5) (EIIS IG: IEEE TRB) portion of the movable incore detector system (EIIS AB: IEEE RPV). The location of the indication was just above the seal table (EIIS IG) outside the heat affected zone of the weld attaching the fitting adapter for a flux thimble to the 3/4" guide tube. After removal of the 1/4" boric acid buildup, there was no visible leakage. After waiting an hour the physical manifestation of a possible leak location was a faint 1/8" long wetted area on the guide tube below the fitting adapter. Prior to system depressurization, the guide tube was liquid penetrant examined and the suspected indication was verified.

At approximately 0600 EST March 10, 1994, an Unusual Event was declared in accordance with EPIP 20101, due to a Technical Specification-required shutdown. NRC and State notifications were completed for the Unusual Event.

The plant was taken off-line on March 10, 1994. The Unusual Event was terminated when the plant reached cold shutdown on March 11, 1994. Required NRC,and State notifications were completed for the termination of the Unusual Event.

The guide tube was repaired by cutting the guide tube below the through-wall indication and welding a new adapter to the remaining tube length. Root and final weld enhanced liquid penetrant testing confirmed an ASME code acceptable weld condition. The pressure integrity of the new weld and compression fittings were verified during the reactor coolant system (RCS) overpressure testing prior to returning the plant to service on March 18, 1994.

II . CAUSE The leak on guide tube N-5 was due to transgranular stress corrosion cracking (TGSCC) which originated at the outside diameter surface and propagated thru-wall. The guide tube consists of 304 stainless steel.

Austenitic stainless steels such as those of the 200 and 300 series are subject to stress corrosion cracking from chlorides when under tensile stress. Sources of stress include residual stress due to manufacturing and cold working from machining and welding. The indication was found outside the heat affected zone of the fitting adapter to guide tube weld.

No source of impinging leakage has been identified in the area. Therefore, the most likely source of chloride contamination was from improper cleaning techniques.

III. ANALYSIS OF THE EVENT Licensin Re uirements Technical Specification 3.4.6.2, Operational Leakage, requires the plant to be in at least 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 /> when any pressure boundary leakage is found. Guide tube N-5 on the seal table is considered part of the pressure boundary. Unit 4 was in hot standby at 1132 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.30726e-4 months <br /> EST on March 10, 1994, and reached cold shutdown at 0325 hours0.00376 days <br />0.0903 hours <br />5.373677e-4 weeks <br />1.236625e-4 months <br /> EST on March ll, 1994.

il 0 lP LICENSEE %NE REPORT (LER)'EXT 7ZINUAEION FACILITY NAME DOCKET NUMBER LER NUMBER PAGE NO.

TURKEY POINT UNIT 4" 05000251 94-002-00 03 OF 03 Anal sis of Effects on Safet There were no adverse consequences as a result of this condition. The leak rate was not detectable by,a water balance or radiation detection systems.

All leakage through the indication was evaporatedthe atseal the site of the leak with no indication of dripping. The tubing at table is currently visually inspected every six weeks.

The failure mechanism found does not represent a safety concern since the tube material (304 SS) is ductile and not subject to brittle crack propagation. Stress corrosion cracking failures in stainless materials will leak long before a critical crack size can be reached. Since these tubes are scheduled to be visually inspected every six weeks, any indication .would be detected shortly after a leak begins.

Nevertheless, had the guide tube suffered catastrophic failure, the si.'ze of the break would have been limited to the capacity of the three-quarter inch outside diameter guide tube. 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 smal'1 .break size is given as a two inch diameter cold leg 'break (3.142 square inch area) .

Therefore, no compromise to the safety of plant personnel or the general public occurred due to this found condition.

IV. CORRECTIVE ACTIONS Immediate:

The plant was shutdown and the leaking guide tube repaired. 'The repair was pressure tested and leak inspected prior to return to service.

Lon Term:

Cleanliness measures for post-maintenance use in the area of the seal table will be reviewed for potential enhancement to provide for,thorough cleaning without chloride exposures V. ADDITIONAL INFORMATION EIIS Codes are shown in the format [EIIS SYSTEM: IEEE component function identifier, second component function identifier (if appropriate)].

The guide tube was supplied by Westinghouse Electric Corp. as material SA 213, Type 304, (304L is acceptable with a .tensile strength of 75 ksi min. and yield strength of 30 ksi min.)

LER 250/93-002 was issued to document a plant shutdown due to pressure boundary leakage at Turkey Point Plant Unit 3.

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