ML17286A782

LER 89-043-01:on 891121,HPCS Sys Immediately Declared Inoperable.Caused by Equipment Failure.Failure Analysis & Determination of Root Cause of HPCS-V-23 Failure Performed & HPCS Operability Surveillance revised.W/910515 Ltr

ML17286A782
Person / Time
Site:	Columbia
Issue date:	05/15/1991
From:	John Baker, Reis M WASHINGTON PUBLIC POWER SUPPLY SYSTEM
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
GO2-91-099, LER-89-043, NUDOCS 9105280113
Download: ML17286A782 (13)

Text

ACCELERATED DISTRIBUTION DEMONS~TION SYSTEM

/

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR: 9105280113 DOC. DATE: 91/05/15 NOTARIZED: NO DOCKET FACIL:50-397 WPPSS Nuclear Project, Unit 2, Washington Public Powe 05000397 AUTH. NAME AUTHOR AFFILIATION REIS,M.P. Washington Public Power Supply System BAKER,J.W. Washington Public Power Supply System RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 89-043-01:on 891121,HPCS sys immediately declared inoperable. Caused by equipment failure. Failure analysis &

determination of root cause of HPCS-V-23 failure performed &

HPCS operability surveillance revised.W/910515 ltr.

DISTRIBUTION CODE: IE22T COPIES RECEIVED:LTR ENCL SIZE:

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

NOTES:

RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 ENG,P.L. 1 1 t

INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DSP 2 2 NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB 7E 1 1 NRR/DLPQ/LHFB11 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/SICB8H3 1 1 RR/ S%/ B8D1 1 1 NRR/DST/SRXB 8E 1 1 G 02 1 1 RES/DSIR/EIB 1 1 RGN5 FILE 01 1 1 EXTERNAL: EG&G BRYCE,J.H 3 3 L ST LOBBY WARD 1 1 NRC PDR 1 1 NSIC MURPHY,G.A 1 1 NSIC POORE,W. 1 1 NUDOCS FULL TXT 1 1 f'og Sg~g74 c NOTE TO ALL "RIDS" RECIPIENTS:

I PLEASE HELP US TO REDUCE WASTE! CONTACT THE 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 33 ENCL 33

0 WASHINGTON PUBLIC POWER SUPPLY SYSTEM P.O. Box 968 ~ 3000 George Washington Way ~ Richland, Washington 9935Z G02-91-099 Docket No. 50-397 Hay 15, 1991 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

NUCLEAR PLANT NO. 2 LICENSEE EVENT REPORT NO. 89-043-01

Dear Sir:

Transmitted herewith is Licensee Event Report No.89-043 Revision 1 for the WNP-2 Plant. This report is submitted in response to the report requirements of 10CFR50.73 and discusses the items of reportabi lity, corrective action taken, and action taken to preclude recurrence.

This supplement provides final root cause information.

Very truly yours, J. W. aker (M/D 927M)

WNP-2 Plant Manager JWB:ac

Enclosure:

Licensee Event Report No. 89-043-01 cc: Hr. John B. Martin, NRC Region V Mr. C. J. Bosted, NRC Site (H/D 901A)

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J EXPIRES: 4130/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFOAMATION COLLECTION REQUEST: 50.0 HRS FORWARD LICENSEE EVENT REPORT (LER) COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REI'ORTS MANAGEMENT BRANCH (F630), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503, DOCKET NUMBER (2) PA 6 3 FACILITY NAME (1)

Mashin ton Nuclear Plant - Unit 2 o s o o o3 97 i OF06 TITLE Ie)

INOPERABILITY OF THE HIGH PRESSURE CORE SPRAY SYSTEM CAUSED BY E UIPMENT FAILURE EVENT DATE IS) LER NUMBER (6) REPORT DATE (7) OTHER FACILITIES INVOLVED (6)

SEOUENTIAL REVISION DAY YEAR FACILITYNAMES DOCKET NUMBER(S)

MONTH DAY YEAR YEAR NUMBER '.,ne NUMBER MONTH o s o o o 2 1 8 9 8 9 0 4 3 0 1 0 515 91 0 5 0 0 0 THIS REPORT IS SUBMITTED PURSUANT T 0 THE REOUIREMENTS OF 10 CFR I'I: (Check onr or morr of the followlnpl (11 OPERATING MODE (9) 20.402(b) 20.405(cl 60.73(e l(2)(iv) 73.71(B)

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SUPPLEMENTAL REPORT EXPECTED (141 MONTH DAY YEAR EXPECTED SUB M I SS 10 N DATE (15)

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At 0524 hours0.00606 days <br />0.146 hours <br />8.664021e-4 weeks <br />1.99382e-4 months <br /> on November 21, 1989, during performance of the High Pressure Core Spray (HPCS) system operability surveillance test, the HPCS minimum flow valve (HPCS-V-12) apparently would not open properly to maintain minimum flow through the pump when system flow was secured. The HPCS system was immediately declared inoperable and troubleshooting was initiated by the Plant operations staff. Initial troubleshooting showed that HPCS-V-12 was not malfunctioning. The problem was isolated to HPCS-V-23, the test return valve to the suppression pool. It was found to be approximately ten percent open. This allowed sufficient flow to cause HPCS-V-12 to close. The LCO Action requirement of technical specification 3.5.1 was imposed until the return of the HPCS system to operable status.

At 2150 hours0.0249 days <br />0.597 hours <br />0.00355 weeks <br />8.18075e-4 months <br /> that evening, as a result of continued troubleshooting efforts, the test return valve to the Suppression Pool (HPCS-V-23), was found to be approximately 10 percent open, even though it was indicating closed in the control room. After attempts to manually close the valve failed, the manual block valve for the test return line (HPCS-V-64) was closed to isolate the faulty valve. At 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br />, after successful completion of the system operability surveillance, the HPCS system was declared operable.

Initially the cause of this event was thought to be equipment failure since HPCS-V-23, the test return line isolation to the Suppression Pool, was not able to be closed by motor operator or by hand to prevent undesired diversion of system flow from the injection path. A failure analysis of HPCS-V-23 was performed after NRC Form 366 (669)

NRC FORM 366A (64)9)

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LICENSEE EVPhg,P =PORT (LER)

TEXT COMBINATION e

'4(I I U.S. NUCLEAR REGULATORY COMMISSION t APPROVED OMB NO. 31500104 EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REQUEST: 500 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (F430), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO 1HE PAPERWORK REDUCTION PROJECT (31504)104), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

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Abstract (contd.)

disassembly and repair of the valve during the R5 outage and showed no internal damage or obstruction. The root cause was indeterminate. There is no safety significance associated with this event. Because HPCS is a Rsingle train" system, its inoperability is reportable, even though at all times during the event the requirements of the WNP-2 Technical Specifications were complied with to maintain the plant within its design basis. The actions of the plant operators were prompt and correct. This event posed no threat to the health and safety of the public or plant personnel.

On October 23, 1990, during the performance of the HPCS operability surveillance test, HPCS-V-23 again indicated closed while HPCS-V-12 failed to open. This event is described in LER-90-025. A subsequent root cause analysis confirmed that HPCS-V-23 did not fully close, during system testing, due to premature torque switch actuation. The investigation also revealed, the valve would not close further in the November 1989 event because the valve was already fully closed. When the HPCS pump .

was secured and the differential pressure relaxed, HPCS-V-23 had enough applied stem thrust to mechanically fully close the valve. Premature torque switch actuation is considered the root cause of both the 1989 and 1990 events.

Corrective actions include:

1) Resetting HPCS-V-23 torque switches to ensure closure under all conditions.

2) Review of design practices to ensure similar cases are identified and corrected.

Plant Conditions a) Power Level - 100K b) Plant Mode - 1 Event Descri tion At 0524 hours0.00606 days <br />0.146 hours <br />8.664021e-4 weeks <br />1.99382e-4 months <br /> on November 21, 1989, during performance of the High Pressure Core Spray (HPCS) system operability surveillance test, the HPCS minimum flow valve (HPCS-V-12) apparently would not open to properly maintain minimum flow through the HPCS pump (HPCS-P-1) when system flow was secured. The HPCS system was immediately declared inoperable and troubleshooting was initiated by the Plant operations staff. Initial troubleshooting was not able to discover the exact reason for the fault. Observed symptoms suggested that the flow indicating switch (HPCS-FIS-6) for the system flow input to the minimum flow valve control circuit might be faulty. At 0910 hours0.0105 days <br />0.253 hours <br />0.0015 weeks <br />3.46255e-4 months <br /> the NRC Bethesda Operations Center was notified that the HPCS system was inoperable under the requirements of 10CFR50.72(b)(2)(iii) as a non-emergency four hour reportable event.

NRC FoIRI 366A (64)9)

NRC FORM 366A US. (ILI.'.r rI'-'EGULATORYCOMMISSION APPROVED OMB NO. 3(504))04 (689)

E X P I R ES I 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT '~" '~",r~"," INFORMATION COLLECTION REOUESTI 500 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P-530), U.S. NUCLEAR

, REGULATORY COMMISSION, WASHINGTON, DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31504)104). OFFICE OF MANAGEMENTANO BUDGET. WASHINGTON. DC 20503, FACILITY NAME (1) D ~(J(t'UMBER (2) LER NUMBER (6) PAGE (3)

~~" II SEOUSNTIAL S@i REVISION NUMSSR NVMSSR Washington Nuclear Plant - Unit 2 p p p p 3 7 8 9 043 0 1 0 3 0F0 6 TEXT /llmore Spree /4 reeo/red, See eddi)/one/ N/IC Form 3664'4/ (12)

At approximately 1300 hours0.015 days <br />0.361 hours <br />0.00215 weeks <br />4.9465e-4 months <br />, troubles voting of the HPCS system showed that the minimum flow valve (HPCS-V-12) functiotIed correctly arid that the system was able to meet the design requirements for flow through the Condensate Storage Tank (CST) test return line (CST to CST flowpath). At 2150 hours0.0249 days <br />0.597 hours <br />0.00355 weeks <br />8.18075e-4 months <br /> that evening, as a result of continued troubleshooting efforts, the test return valve to the Suppression Pool (HPCS-V-23), appeared to be approximately 10 percent open. The valve, in fact, indicated closed in the control room. After attempts to close the valve with the motor operator and manual operator failed, the manual block valve for the test return line (HPCS-V-64) was closed to isolate the faulty valve from the remainder of the system. The attempts to manually close the valve failed because, in the absence of the differential pressure due to the pump operation, HPCS-V-23 had enough applied stem thrust to mechanically drive the valve fully closed. At 2230 hours0.0258 days <br />0.619 hours <br />0.00369 weeks <br />8.48515e-4 months <br />, after successful completion of the system operability surveillance, the HPCS system was declared operable.

Immediate Corrective Action Plant operators responded in a timely manner to follow the requirements of plant procedures and technical specifications. They initially identified the condition, applied the restrictions of the LCO Action requirement of technical specification

3. 5. 1 and then followed up with appropriate action to obtai n resolution. Initially, the problem manifested itself as failure of the minimum flow valve to open when system flow was apparently secured. In fact, flow through the pump was just above the required value for minimum flow, most probably due to the pathway provided by HPCS-V-23 not being completely closed. Flow was just sufficient to pick up flow switch HPCS-FIS-6, thus preventing the minimum flow valve from opening. Subsequent troubleshooting verified that the minimum flow valve, HPCS-V-12, and its associated flow indicating switch and controls were operating correctly. The problem was then localized to the failure of HPCS-V-23 to completely close after it was discovered that the motor operator had stopped at the 90 percent closed position as a result of torque switch actuation.

Further Evaluation and Corrective Action A. Further Evaluation

1. The original event was reported per the requirement of 10CFR50.73(a)(2)(v) as a "condition that alone could have prevented the fulfillment of the safety function of structures or systems that are needed to: (A) Shut down the reactor and maintain it in a safe shutdown condition; (B) Remove residual heat; (C) Control the release of radioactive material; or (D)

Mitigate the consequences of an accident." The inoperability of the HPCS system is a unique event at WNP-2. Unlike the other Emergency Core Cooling Systems, HPCS system inoperability is reportable even though all requirements of technical specification LCO action statements are being complied with. This is so because Cooling System and, as such, is reportable any time it is a "single train" Emergency Core it is unable to perform its safety function when it is required to be able to do so by plant conditions.

0 0 A

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NRC FORM 366A U.S. NUCLEAR REGULATORY COMMISSION APPROVED OMB NO, 3')600106 (BJ(9) t EXPIRES: i/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REQUEST: 600 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (F630), U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON, OC 2055S, AND TO THE PAPERWORK REDUCTION PROJECT (31604)Oi). OFFICE OF MANAGEMENTAND BUDGET. WASHINGTON, DC 20503.

FACILITYNAME (11 DOCKET NUMSER (2) LER NUMBER (6) PAGE (3)

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2. The preliminary cause of this event was thought to be equipment failure since HPCS-V-23 the test return line isolation to the Suppression Pool, was not able to be closed to prevent undesired diversion of system flow.

The valve was initially unable to be closed either with the motor operator or by hand.. The root cause of this event had not been determined due to the need to disassemble HPCS-V-23 in order to complete the investigation.

Technical evaluation by plant staff and communication with the valve manufacturer, Anchor-Dar ling Company, indicated that the cause of the fai1ure could have been vibration induced loosening of the disk nut. This type of failure would allow the valve disk to become misaligned with the disk guides/valve seat area and possibly result in the failure of the valve to attain the completely closed position. Similar failures of this type of valve have apparently occurred at other plants which exhibited the same types of symptoms.

3. During the R5 Refueling Outage (5/90), HPCS-V-23 was disassembled and inspected. All mechanical parts were found satisfactory and no obstruction was present. At the end of the outage, the root cause investigation was completed and, based on available information, the root cause was concluded to be indeterminate.

After the event was repeated on October 23, 1990, another root cause analysis was performed. A Motor Operated Valve Analysis and Test System (MOVATS) diagnostic test of HPCS-V-23 under dynamic conditions confirmed that the valve did not close fully due to the premature torque switch actuation. Investigation revealed that the test conditions are more severe than the design requirements.

It was determined the root cause of the event was the less than adequate design specification, in that the calculation that determined the minimum required thrust for HPCS-V-23 did not consider differential pressure at survei'llance test conditions.

B. Further Corrective Action The failure analysis and determination of the root cause of the HPCS-V-23 failure was performed after completion of disassembly and repair of the valve during the Spring 1990 Refueling and Maintenance outage.

2. HPCS-V-23 thrust was recalculated and torque switches reset to ensure proper closure under both test and accident conditions.

3. A note was added to the MOV Master Data Sheet for HPCS-V-23 to state "This valve is routinely tested at higher differential pressure than the design differential pressure."

NRC FORM 366A U.S. NUCLEA APPROVEO OMB NO. 31500)04 (84)9)

EXPIRES: 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS LICENSEE EVENT REPORT (LER) INFORMATION COLLECTION REOUEST: 50.0 HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS TEXT CONTINUATION AND REPORTS MANAGEMENT BRANCH (P.530), U.S. NUCLEAR REGULATORY COMMISSION, WASHINGTON. DC 20555, AND TO

')ME PAPERWORK REDUCTION PROJECT (31504)104), OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3)

SEQUEMTIAL %3 REVSION NUMBER <%6 NUM8Err 0 5 0 0 0 OF TEXT /I/ moro 4/rooo /4 roqo/rod, riro oddd4ror//VRC Fomr 3664'4/ (17)

4. The HPCS operability surveillance procedure will be revised to verify HPCS-V-12 opens when HPCS-V-23 closes and to record the flow rate when HPCS-V-23 is stroked closed against differential pressure.

5. Valve thrust calculations based on test data will be reviewed to determine if operations differential pressures exceed design basis assumptions.

6. The design differential pressure calculation process will be revised to require valves be identified, whose surveillance conditions are more severe than their design differential pressure conditions.

Safety Si nificance t

There is no safety significance associated with this event. Since subsequent analysis demonstrated that HPCS-V-23 fully closed after test condition differential pressures were removed, the HPCS function was not actually impaired. (The valve is assumed to be closed during HPCS injection.) The valve completed its full closure when returning the system to standby alignment. A demand for HPCS injection during test conditions would have reduced the differential pressure across the valve by providing an alternate flow path. The reduced differential would most probably have allowed the valve to fully close, directing all HPCS flow to the reactor vessel.

Failure of the HPCS system is within the bounds of the ECCS single failure criteria assumed in the FSAR safety analyses and does not prevent the ECCS from performing its safety function in response to a DBA.

At all times during the event, the requirements of-the MNP-2 Technical Specifications (Section 3.5.1) were complied with. The LCO action for this section requires ensuring the operability of the redundant ECCS Divisions 1 and 2 and the Reactor Core Isolation Cooling system while the HPCS system is inoperable (a maximum of 14 days is allowed). The entire period of inoperability was less than one day.

The actions of the plant operators were prompt and correct to ensure the plant was maintained within the bounds of the technical specifications and therefore within the bounds of the operational safety analysis. Since no safety significance is associated with this event, it posed no threat to the'health and safety of the public or plant personnel..

Similiar Events There are four instances of HPCS system inoperability that were evaluated as similar to this LER. LER 84-030 "Unscheduled Lockout of the High Pressure Core Spray Diesel Generator (HPCS-DG)U documented an event during which a technician inadvertently locked out the HPCS Diesel Generator during surveillance activity by incorrect placement of an electrical jumper. The corrective action consisted of revising the procedure to add a caution note and to designate the proper contacts to be jumpered.

NRC Form 366A (669)

NRC FORM 366A

$ 4)9)

LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION V.S, NUCLEAR REGULATORY COMMISSION t APPROVED OMB NO. 31500104 E XP I 8 E S I 4/30/92 ESTIMATED BURDEN PER RESPONSE TO COMPLY WTH THIS INFORMATION COLLECTION REOUEST.'0AI HRS. FORWARD COMMENTS REGARDING BURDEN ESTIMATE TO THE RECORDS AND REPORTS MANAGEMENT BRANCH (P.530). U.S. NUCLEAR REGULATORY COMMISSION. WASHINGTON. DC 20555, AND TO THE PAPERWORK REDUCTION PROJECT (31500104). OFFICE OF MANAGEMENTAND BUDGET, WASHINGTON, DC 20503.

FACILITYNAME (I) DOCKET NUMBER (2) LER NUMBER (6) PAGE 13)

SSOUSNTIAL N% REVISION NUMBER Ors-"'UMSSII Washin ton Nuclear Plant - Unit 2 0 5 0 0 0 3 7 8 4 3 0 1 0 OF 0 6 TEXT /// moro speed /4 redo/red, Iree eddhionel /VRC %%drrn 3664'4/ (Ill LER 85-022 RHPCS System Inoperable" documented an event during which plant personnel inadvertently disconnected system initiation logic while repairing two sheared off HPCS initiation status lamp sockets. Corrective action consisted of notifying plant operations, maintenance and technical personnel to place additional reliance on electrical wiring diagrams, connection diagrams and approved vendor manuals when appropriate.

LER 89-030 NHigh Pressure Core Spray System Inoperable Caused by Suppression Pool Pump Suction Valve Failure Due to Motor Dperator Manufacturing Error" documented an event during which the HPCS system was declared inoperable due to failure of the suppression pool pump suction valve motor operator during performance of the operability surveillance. The corrective actions associated with this LER consisted of: checking other valve motor operators during the next refueling outage, revising

. the plant maintenance procedures to add instructions for inspection of the motor operators, adding precautions to plant procedures regarding disposition of valves found difficult to operate, and initiation of a 10CFR21 report.

.LER 90-025 " Inoperability of the High Pressure Core Spray System Caused by Equipment Failure" documented an event in which the HPCS-V-23 failed to fully close and HPCS-V-12 failed to open during the surveillance testing of HPCS. Because the events were so similar, the corrective actions are essentially the same.

EI IS Information Text Reference EI IS Reference

~Sstem ~Com anent HPCS System BG HPCS-V-12 BG .. V HPCS-V-23 BG V HPCS-P-1 BG P HPCS-F IS-6 BG FIS Suppression Pool BT HPCS-V-64 BG ECCS Division 1 BM ECCS Division 2 BM RCIC System BM Condensate Storage Tank KA TK NRC Form 366A (64)9)