ML17229A344

LER 97-005-00:on 970419,reactor Was Shutdown Due to Reactor Coolant Pressure Boundary Leakage.Hot Cracking Was Caused by Weld Contamination.Repairs to RCPB Were Completed & 1A SDC Train Was Restored to Svc

ML17229A344
Person / Time
Site:	Saint Lucie
Issue date:	05/13/1997
From:	Benken E, Stall J FLORIDA POWER & LIGHT CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
L-97-130, LER-97-005, LER-97-5, NUDOCS 9705200337
Download: ML17229A344 (11)

Text

i 1 CATEGORY 1 Q INFORMATION l REGULATORY DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9705200337 DOC.DATE: 97/05/13 NOTARIZED: NO DOCKET FACIL: --.3-335 St. Lucie Plant, Unit 1, Florida Po~er & Light Co. 05000335 AUTH. NAME AUTHOR AFFILIATION BENKEN,E.J. Florida Power & Light Co.

STALL,J.A. Florida Power & Light'o.

RECIP.NAME RECIPIENT AFFILIATION E

SUBJECT:

I ER 97-005-00:on 970419,reactor was shutdown due to reactor coolant pressure boundary leakage. Repairs to RCPB was completed & la SDC train was restored to svc.W/970513 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 G ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD2-3 PD 1 1 WIENS,L. 1 1 0 INTERNAL: ACRS 1 1 2 2 AEOD/SPD/RRAB 1 1 1 1 NRR/DE/ECGB 1 1 NRR/DE/EELB 1 1 NRR/DE/EMEB 1 1 NRR/DRCH/HHFB 1 1 NRR/DRCH/HICB 1 1 NRR/DRCH/HOLB 1 1 NRR/DRCH/HQMB 1 1 NRR/DRPM/PECB 1 1 NRR/DSSA/SPLB 1 1 NRR/DSSA/SRXB 1 1 RES/DET/EIB 1 1 RGN2 FILE 01 1 1 EXTEi NAL: L ST LOBBY WARD 1 1 LITCC BRYCE,J H 1 1 D NOAC POORE g W ~ 1 1 NOAC QUEENER,DS 1 1 NRC PDR 1 1 NUDOCS FULL TXT 1 1 0 N

NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE WASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM OWFN SD-5(EXT. 415-2083) TO ELIMINATE YOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

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,J Florida Power 8 Light Company, 6501 South Ocean Drive, Jensen Beach. FL34957 May 13, 1997 L-97-130 10 CFR 50.73 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Re: St. Lucie Unit 1 Docket No. 50-335 Reportable Event: 97-005 Date of Event: April 19, 1997 Reactor Shutdown Required by Technical Specifications The attached Licensee Event Report is being submitted pursuant to the requirements of 10 CFR 50.73 to provide notification of the subject event.

Very truly yours, J. A. Stall Vice President St. Lucie Plant JAS/EJB Attachment cc: Regional Administrator, USNRC Region II I (

Senior Resident Inspector, USNRC, St. Lucie Plant 9705200337 9705i3 PDR ADOCK 05000335 S PDR p QttUQ(i 4

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII an FPL Group company

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED SY OIM No. 31604104 EKFNIES 04nolss (4.95)

ESTIMATED SVROEN PER RESPONSE To COMPLY WITH THIS MANDATO INFORMATION COLLECTION REQUEST: 60.0 HRS. REPORTED LESSON LEARNED ARE INCORPORATED INTO THE UCENSING PROCESS ANO F SACK To eIOUSTRY. FORWARD COMMDITS REGARDING SURD EN ESTIMAT LICENBEE EVENT REPORT (LER) TO THE INFORMATION ANO RECORDS MANAGEMENT BRANCH IT.e F33)

VN. NUCLEAR REGIAATORY COMMISSION. WASHINGTON, OC 206660001 AND TO THE PAPERWORK REDUCTION PROJECT I31600104b OFRCE 0 (See reverse for required number of MANAGEMENTAND BUDGET, WASHINGTON, OC 20603.

digits/characters for each block)

FACIUTY NAME (1) DOCKET NNASBE 12l PAGE Isl ST LUCIE UNIT 1 05000335 1 OF 7 TITLE 14l Reactor Shutdown Required by TechnicaI Specifications due to Reactor Coolant Pressure Boundary Leakage FACIUTY NAME DOCKETNUMSER MONTH DAY SEauENTIAL REVISION MONTH DAY YEAR NUM9ER NUMBER N/A FACIUTY NAME DOCKETNVMSER 04 19 97, 97 005 00 05 13 97 N/A OPERAT)NQ MODE (6) 20.2201(b) 20.2203 (0) (2) (v) 50.73 (0) (2) (i) 50.73(n) (2)(viii)

POWER LEVEL l10) 20.2203(e) l2)(i) 20.2203(o) l3) Iii) 50.73(n) (2)(iii) 73.71 OTHER 20.2203 (0) l2) (iii) 50.36(c)ll) 50.73(n)(2)(v) Specify ln Abstract below or lri NRC Form 3SSA 20.2203(n) (2) (iv) 50.36(c)(2) 50.73(n)(2)(vii)

NAME TELEPHONE NVMSER Onc4de Ates Coal Edwin J. Benken, Licensing Engineer (561) 467 - 7156 REPORTABLE REPORTABLE CAUSE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER TO NPRDS TO NPRDS

'.jViE:kj BP N/A N MONTH DAY YEAR EXPECTED YES SUBMISSION (lf yes, complete EXPECTED SUBMISSION DATE) ~

X No DATE l15)

ABSTRACT (Umit to 1400 spnces, i.o., npproximote(y 15 single-specod typowritten lines) l16)

On April 18, 1997, St, Lucie Unit 1 was operating in Mode 1 at 100 percent reactor power. Leakage from a one inch line on a safety injection (Sl) pipe vent was identified and subsequently determined to be reactor coolant pressure boundary (RCPB) leakage. The leakage was restricted to Safety Injection

~ Tank 1B2 inventory, and no reactor coolant leakage resulted. A reactor. shutdown was initiated on April 19, 1997, and was completed in accordance with Technical Specification requirements. The Unit was placed in Mode 5 on April 20, 1997, to implement repairs. During the plant cooldown, shutdown cooling (SDC) train 1A was declared inoperable and the redundant train was used to complete the cooldown. The RCPB leakage was repaired and the Unit was subsequently returned to Mode 1 operation on April 23, 1997.

The plant shutdown was required by Technical Specifications due to the, presence of pressure boundary leakage. The failure mechanism associated with the pressure boundary leakage was determined to be hot cracking of a socket weld associated with the Sl vent line. The hot cracking was caused by weld contamination. The inoperability of the 1A SDC train was due to the misalignment of a minimum flow recirculation line, and the presence of gas voids in the high points of the 1A SDC suction line.

Corrective Actions Include: 1) Repairs were completed to the RCPB and the 1A SDC train was restored to service. 2) Additional analysis was performed to confirm the failure mechanism for the affected socket weld. 3) Weld testing is being performed to evaluate for potential improvements. 4) The 1A SDC train was restored to operation following venting and inspection. 5) SDC system venting procedures are being revised to include additional frequency and temperature requirements, NRc FORM 38$ I4.95)

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSIO I4 95I LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 2 OF 7 97 005 00 TEXT llfmore speceis required, use eddi tionel copies of OftC Form 366AJ I17I On April 17, 1997, St. Lucie Unit 1 was operating in Mode 1 at 100 percent reactor power. At 1037, a High Pressure Safety Injection (HPSI) Pump [EIIS:BQ:P] was started and inventory was added to the Safety Injection Tanks (SIT) in accordance with normal operating procedures. Following the SIT fill evolution, operators noted that the 1B2 SIT [EIIS:BP:TK] level was slowly decreasing. The rate of inventory loss in the SIT was observed to be approximately 2.5 percent over a 6 hour6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> period.

Additionally, operators noticed an increase in reactor cavity leakage from approximately 0.2 gpm to 0.45 gpm. Based on the indicated increase in reactor cavity leakage, a reactor coolant system (RCS)

[EIIS:AB] inventory balance was performed to evaluate and quantify RCS leakage. The inventory balance determined that no change in RCS leakage rate had occurred and values were consistent with those determined prior to filling the SITs. An investigation was initiated to determine the source of the indicated increase in reactor cavity leakage.

On April 18, 1997, while conducting a containment inspection to identify the source of the leakage, water was observed in the area of the 1B2 SIT pipe trench. To minimize radiological exposure, a robotic camera was deployed to determine the source of the leakage, which appeared to originate from

+he vicinity of vent valve V-3" 15 [EIIS:BP:VTV]. This vent valve is located within the reactor containment building (RCB) on the 1B2 safety injection pipe, upstream of the 1B2 safety injection loop check valve (Refer to Figure 1). A sample of leakage was obtained and analyzed, which indicated a boron concentration in the sample of 2915 parts per million (ppm). RCS boron concentration at the time was approximately 840 ppm.

t A reduction in reactor power was initiated at 2020 on'April 18, 1997, to allow personnel to access V-3815 and characterize the source of the leakage. At 0150 on April 19, 1997, with the reactor in Mode 2 at approximately 10'ercent power, a containment entry was made to inspect V-3815. The inspection revealed a failure. of the socket weld joining the one inch vent line for V-3815 to the sockolet in the safety injection loop line. This was determined to be reactor coolant pressure boundary (RCPB) leakage, in accordance with 10 CFR 50.2, and the action statement for Technical Specification (TS) 3.4.6.2 was entered at 0217 hours0.00251 days <br />0.0603 hours <br />3.587963e-4 weeks <br />8.25685e-5 months <br />. Action Statement 3.4.6.2.a, specifies, "With any PRESSURE BOUNDARY LEAKAGE, be in at least HOT STANDBY 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 within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />."

A reactor shutdown was commenced and St. Lucie Unit 1 entered Mode 3 (Hot Standby) at 0228 on April 19, 1997. A Notification of Unusual Event was made to the State of Florida at 0229'and to the USNRC at 0245, in accordance with the requirements of the St. Lucie Emergency Plan for events involving RCS pressure boundary leakage. The Unit entered Mode 4 at 1405 and the 1B shutdown cooling (SDC) train [EIIS:BP] was placed in service at 2322 hours0.0269 days <br />0.645 hours <br />0.00384 weeks <br />8.83521e-4 months <br /> on April 19, 1997. Operators attempted, but were unable, to place the 1A SDC train in service due to a decrease in pressurizer

[EIIS:AB:PZR] level when the suction valves for the 1A SDC train were opened. The 1A SDC train was subsequently declared inoperable, and the plant cooldown was continued using the 1B SDC train. Unit 1 entered Mode 5 on April 20, 1997, at 0315 and the Unusual Event was terminated at that time.

Following repaiI af the affected weld on the 182 safety injection line and resto.dtion of the

'A SDC train, St. Lucie Unit 1 retuined to Mode 1 power operation at 0153 on April 23, 1997.

NRC FOIIM 366A U.S. NUCLEAR REGULATORY COMMISSIO (4-95)

LICENSEE EVENT REPORT (LER)

. TEXT CONTINUATION YEAR SEOUENTIAL REVISION ST. LUCIE UNIT 1 05000335 3 OF 7 97 005 00 TEXT Iifmore speceis required, use edditionel copies of IVRC Form 366AI I17I The reactor shut down was completed in accordance with TS requirements for RCS leakage involving the reactor coolant pressure boundary. 'he RCPB leakage originated from a socket weld on a one inch vent line to V-3815, located on the 1B2 safety injection header. While only 1B2 safety injection tank volume was affected, and no reactor coolant inventory was lost as a result of the leak, the site of the leakage is classified as reactor coolant pressure boundary, as further discussed in this report.

Failure analysis of the affected weld on the vent line to V-3815 was performed following the event.

The analysis concluded that the initiating failure mechanism was hot cracking of the weld due to contamination. Boric acid residue is considered to be the most likely cause of this contamination.

The 1A SDC train was declared inoperable when operations personnel observed decreases in pressurizer

. level while opening the SDC suction isolation valves. Local observations identified that system pressure in the 1A SDC train was fluctuating during attempts to open the valves, and a safety relief valve on the 1A SDC train, V-3483, temporarily lifted as designed in response to the system pressure transient.

Subsequent inspection and trouble shooting of flow noises in system piping by operations personnel identified that a manual recirculation isolation valve (V-3"<4) for the 1A low pressure safety injection (LPSI) pump was not fully shut as required for SDC operation. This resulted in a flow path from the RCS to the refueling water tank (RWT) when the SDC suction valves to the pump were opened, and was the primary cause of the indicated decreases in pressurizer level previously discussed. Upon inspection, the handwheel for V-3204 was found to be difficult to operate and appeared to be closed, however operators using a valve wrench were able to manipulate the valve an additional two turns to the fully closed position. A work order was written to repair the defective valve and preventive maintenance practices are being reviewed to address generic aspects.

System venting and inspections performed following the event determined that the pressure response observed in the 1A SDC train was caused by the presence of gas voids in the high points of the 1A SDC suction piping in conjunction with a partially open LPSI pump recirculation valve. The presence of voids, along with the partially open recirculation valve would provide conditions conducive to steam flashing and pressure fluctuations in the LPSI pump suction line when reactor coolant was initially aligned to the system. Venting of the SDC piping is required to be performed following system use as the result of a similar event in 1995, however the procedures did not specifically require that this be performed at ambient temperature. The completion of venting following the last use of the SDC system may therefore not have been adequate to prevent subsequent degassing (voiding) of reactor coolant in the SDC suction lines. Consequently, procedural inadequacy was a contributing factor by not preventing conditions which were favorable to the formation of the'gas voids in the 1A SDC system.

TS 3.4.6.2 requires that no pressure boundary leakage be present in Modes 1,2,3 and 4. TS Action Statement 3 4.6.2.a, further specifies, "With any PRESSURE BOUNDARY LEAKAGE, be in at least HOT STANDBY 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 within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />." St. Lucie Unit 1 vas placed in Mode 3, HOT S ANDBY e';0228, on April 19 1997, approximately 23 minutes following the identification of RCPB leakage.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSIO I4.96)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 4 OF 7 97 005 00 TEXT le more speoeis required, use eddidonel copies of NRC Farm 386AJ I17)

The plant'entered Mode 5 at 0315 on April 20, 1997, approximately 25 hours2.893519e-4 days <br />0.00694 hours <br />4.133598e-5 weeks <br />9.5125e-6 months <br /> after entry into Mode 3.

Based on the above, this event is reportable under 10 CFR 50.73 (a) (2) (i) (A), as a completion of a plant shutdown required by the Technical Specifications.

According to the definition provided in the St. Lucie Unit 1 TS, PRESSURE BOUNDARY LEAKAGE is defined as "...leakage (except steam generator tube leakage) through a non-isolable fault in a Reactor Coolant System component body, pipe wall or vessel. wall." Additionally, 10 CFR 50.2 defines the "reactor coolant pressure boundary" as follows:

...all those pressure-containing components of boiling or pressurized water-cooled nuclear power reactors such as pressure vessels, 'piping, pumps and valves, which are:

(1) Part of the reactor coolant system, or (2) Connected to the reactor coolant system, up to and including any and all of the following:

The outermost containment isolation valve in system piping which penetrates primary reactor containment, The second of two valves normally closed during normal reactor operation in system piping which does not penetrate primary reactor containment, The reactor coolant system safety and relief valves.

During this event, a small amount of inventory from the 1B2 SIT was observed leaking from a weld associated with a one inch vent,- V-3815, located on the 1B2 safety injection pipe, upstream of the 1B2 safety injection loop check valve. Per the above definition, this vent is a part of the reactor coolant pressure boundary since it is located on a system connected to the RCS and is within the outermost containment isolation valve in system piping penetrating the primary reactor containment.

Additionally, V-3815 is located in the Quality Group A portion of the safety injection system. This Quality Group is described by the St. Lucie Unit 1 Updated Final Safety Analysis Report (UFSAR),

Section 3.2, as specifically applying to reactor coolant pressure boundary components.

The St. Lucie Unit 1 TS bases related to RCPB leakage specify that pressure boundary leakage of any magnitude is unacceptable as it may be indicative of impending further pressure boundary the presence of any pressure boundary leakage requires that the plant be promptly placed in failure.'herefore, a cold shutdown (Mode 5) condition. Compliance with the Limiting Conditions for Operation (LCO) as specified in the Technical Specifications assures that the functional capability of equipment required for the safe operation of the plant is maintained. Following the identification of pressure boundary leakage during this event, operators promptly implemented the applicable TS Action requirements.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSIO I4.95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 5 OF 7 97 005 00 TEXT llfmore spece is required, use eddi tianel copies of fVRC Form 366A J I17I A review of similar documented maintenance weld failures at St. Lucie was performed following the event. Based on available information, it was determined that no significant failure rate existed for this failure mechanism, therefore the socket weld leakage from the vent line for V-3815 is considered to be a random failure. As a result of the RCBP leakage, no loss of reactor coolant system inv'entory occurred, and the area of leakage was isolated from the RCS by the 1B safety injection header loop check valve (V-3247) [EIIS:BP:VJ. V-3247 is also addressed by the St. Lucie Unit 1 TS and is required to meet periodic surveillance criteria for leakage which provides added assurance of valve integrity.

Leakage from the 1B2 SIT during the event was limited to approximately one-half gallon per minute and makeup was provided as necessary to maintain the required tank volume. The operability of the 182 Sl was not affected by the weld leakage.

N With regard to the 1A SDC system, St. Lucie Unit 1 Updated Final Safety Analysis (UFSAR), Section 9.1.5.3.2, states that " No single failure of an active component during residual heat removal will result in a loss of core cooling capability. The reactor coolant system can be brought to refueling temperature IIsing one Iow pressure safety injection pump and one shutdown cooling heat exchanger." The 1B SDC system remained operational at all times during this event, and was not affected by the inoperability of the 1A SDC train. The 1B SDC train was placed in service to facilitate the RCS cooldown and functioned properly in establishing Mode 5 conditions. The RCS heat removal safety function was maintained at all times during the event.

Following the event, FPL engineering personnel performed a walkdown of the 1A SDC system and reviewed data observed during efforts to place the 1A SD system in service. Based on the pressures in the system observed during the event, a review of the design and hydrostatic testing for this system, and local inspection, the 1A SDC train was determined to be functional and acceptable for operation.

Based on the above, this event did not adversely affect the protection of the health and safety of the public.

Following the identification of the pressure boundary leakage on the 182 safety injection header, St. Lucie Unit 1 was placed in Cold Shutdown in accordance with the requirements of plant Technical Specifications.

2. The affected '! B2 safety injection header vent line weld was removed and repairs were implemented. The Unit was returned to Mode 1 power operation on April 23, 1997,

~

following completion of the repairs.

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSI I4-95I I

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIE UNIT 1 05000335 6 OF 7 97 005 00 TEXT fifmore speceis required, use additional copies of NRC Farm 366AJ I17I

3. An inspection and failure analysis was performed for the failed socket weld associated with V-3815 vent line. The analysis determined that the initiating failure mechanism of the socket weld was hot cracking, due to contamination of the weld. While this failure is considered to be random at St. Lucie, additional testing will be done to evaluate boric acid weld contamination and determine if additional preventive measures are necessary to minimize the potential for recurrence.

The 1A SDC train was returned to service following system venting and the realignment of the minimum flow recirculation valve for the 1A LPSI pump. A caution tag was placed on the recirculation valve and a plant work order was initiated to repair and restore the valve to satisfactory operation.

5. Venting of the 1A LPSI pump suction line is currently being performed at an increased frequency and the results will be evaluated to determine if additional changes to venting periodicity are required.

6. To further preclude the possibility of gas formation in the SDC suction lines, St. Lucie Unit 1 and 2 shutdown cooling system procedures are being revised to require that system venting following SDC operation be conducted at ambient temperatures. FPL engineering will review the procedure revisions for incorporation of adequate guidance and corrective actions prior to issue.

Component: Safety Injection Pipe 1 inch Vent Line - Socket Weld Material: Piping - 304/316 stainless steel with ER 308/316 filler material Sockolet - 304 stainless steel LER - 389/95-001 St. Lucie Unit 2 (2/21/95) - The event describes the failure of a low pressure safety injection (LPSI) pump during a surveillance, due to air binding of the pump. The root cause was attributed to the migration of trapped air in the emergency core cooling system (ECCS) header following maintenance.

In-house Event 95-09 St. Lucie Unit 1 (2/27/95) - This event involved the lifting of safety relief valve V-3483 at St. Lucie Unit 1 following the initiation of flow from the 1A LPSI pump during SDC operation. The primary cause was pressure spiking in the hot leg suction line due to a rapid increase in system flow rate following LPSI pump start. Gas voiding was considered as a possible contributor. Corrective actions were implemented following the event to minimize transient fluid flow effects.

NKC FORM 366A I4.95]

NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSI I4 95)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION YEAR SEQUENTIAL REVISION ST. LUCIF UNIT 1 05000335 7 OF 7 97 005 00 TEXT /ff more speceis required, use edditionel copies of iVRC Form 388A/ I17I BQUB~

SAFETY INJECTION TANK (SIT 1B2)

(SIMPLIFIED DIAGRAM)

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LT REFUELING WATER TANKT RETURN (f-- s

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S SAMPLE O SIAS CLOSE B-e I M

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SIAS hs'ROM V3815 AREA OF LEAKAGE RCS LOOP 182 HPSI PUMP