ML17303A431

LER 87-013-00:on 870510,shutdown Commenced Per Tech Spec 3.8.3.1 Due to Inoperable Inverter.Caused by Loose Silicon Controlled Rectifier (Scr).Loose SCR Replaced & Other SCRs retorqued.W/870608 Ltr

ML17303A431
Person / Time
Site:	Palo Verde
Issue date:	06/08/1987
From:	Bradish T, Haynes J ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
192-00225-JGH-T, 192-225-JGH-T, LER-87-013-01, LER-87-13-1, NUDOCS 8706160395
Download: ML17303A431 (7)

Text

REQUL*T 'NFORMATION DISTR IBUTIO 'YSTEM (RIDS)

• CCESSION NBR: 87061603'P5 DOC. DATE: 87/06/08 NOTARIZED: NO DOCKET FAG IL: STN-50-52'P Palo Verde Nuclear Stationi Unit 2i Arizona Pub i 05000529 1 AUTH. N*ME AUTHOR AFFILIATION BRADISHi T. R. Ari zona Nuclear Paver Prospect (f'ormerlg Arizona Public Serv HAYNES'. G. Arizona'Nuclear Power Prospect (formerly Arizona Public Serv REC IP. NAME 'EC IP IENT AFF lLIAT ION

SUBJECT:

LER 87-013-00: on 870510'hutdown commenced per Tech Spec

3. 8. 3. 1 due to inoperable inverter. Caused bg loose silicon controlled rectikier (SCR). Loose SCR replaced 5 other SCRs retorqued. W/870608 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR ENCL SIZE:

TITLE: 50. 73 Licensee Event Report (LER) i Incident Rpti etc.

NOTES: Standardized plant. M. Davis'RR: iCg. 05000529 RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 L* 1 1 PD5 PD 1 LICITRAiE 1 1 DAVIS> M 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 AEOD/DOA 1 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 DEDRO 1 NRR/DEBT/*DE 1 0 NRR/DEST/ADS 1 0 NRR/DEBT/CEB 1 1 NRR/DEST/ELB 1 1 NRR/DEST/ICSB 1 1 NRR/DEBT/MEB 1 '1 NRR/DEST/MTB 1 1 NRR/DEST/PSB NRR/DEST/RSB 1 1 NRR/DEBT/SGB 1 1 NRR/DLPG/HFB 1 1 NRR/DLPG/GAB 1 1 NRR/DOEA/EAB 1 1 NRR/DREP/RAB 1 NRR/DREP/RPB 2 2 NRR/ MAS/ILRB 1 1 NRR/PMAS/PTSB 1 1 02 1 RES DEPY Gl 1 1 RGN5 FILE 01 1 1 EXTERNAL: EGSQ GROHi M 5 5 H ST LOBBY NARD 1 1 LPDR 1 NRC PDR 1 1 NSIC HARRIS> J 1 NSIC MAYST G 1 NOTES:

TOTAL NUMBER OF COPIES REQUIRED: LTTR 44 ENCL 42

4 NRC Form 244 U.S. NVCLEAR REOULATORY COMMISSION (7 52)

AppRDYED DMs No. 2)fioo)OI LICENSEE EVENT REPORT (LER) EXPIRES; SISI/04 F AC I LITY N A ME (I I DOCKET NUMSER (2) PA E TITLE Palo Verde Unit

(~I 2 0 s 0 0 o 529 >oFO 3 Loose Silicon Controlled Rectifier In Inverter Forces Unit Shutdown EVENT DATE (SI LER NUMSER LS) REPORT DATE (7) OTHER FACILITIES INVOLVED (4) 4 4 DUE Nv I AL rleViSIQN MONTH DAY FACILITYNAMES DOCKET NUMSERIS)

MONTH DAY YEAR YEAR NUMSE tr NUM44 rr YEAR N A 0 S 0 0 0 0 5 10 8787 0 1 3 0 0 8 7 N/A 0 5 0 0 0 OPERATINO THIS REPOR'7 IS SUSMITTED PURSUANT T 0 THE REDUIREMENTs oF 10 cf R ()I Icnece one or more of tne forrowinpf (11)

MODE (4)

] 20.402(4) 20.405 Ic) 50.724((2)(rv) 72.7104)

POWER 20.e05( ~ II I I(i) 50.54(cl (I I 50.72(el)2)(vl 72.71 (cl LEYEL 0 2 0 20AOS ( ~ I (I I (4 I SO.SS(c) (21 50,72(e l(2((vie) OTHER ISpecrfy In Aottrect pvlow enrf In Feet, iYIIC Form 20.405( ~ l(1) (it i) 50,72( ~ ) (2)(i) 50,72( ~ ) (2) (viiI I (A) 266l I 20.405(el(1 I(iv) 50.724) (2) (ii) 50.72(e) (2)(v(4 l(SI 20AOS( ~ Illl(v) 50.7 24) (2) (iii) 50.72( ~ ) (2)(el LICENSEE CONTACT FOR THIS LER (12)

NAME TELEPHONE NUMSER AREA CODE T. R. Bradish, Compliance Supervisor (Ext. 6936) 602 932 5 300 COMPLETE ONE LINE FOR EACH COMPONENT FAILURE DESCRISED IN THIS REPORT (12) gNV4+%N'ne CAUSE SYSTEM COMPONENT MANVFAC TURER EPORTASLE NPRDS

'$ ~@ ')(,P~~gr'O CAUSE SYSTEM COMPONENT MANVFAC. EPORTASLE (r~wzv Qrn~cc+v~q TVRER TO NPRDS B E J IN V TE 209 Y SUPPLEMENTAL REPORT EXPECTED (14I MONTH DAY YEAR EXPECTED SVSMISSION DATE (15)

YES Itf yet, cornprete EXPECTED SVSMISSIOiY DATE) NO ASSTRACT ILimit to IC00 tpecet, I ~ ., epprovfmerefy Sfteen tfnpre epece typewrftren finer) HS)

At 1532 on May 10, 1987 Palo Verde Unit 2 was in Mode 1 (POWER OPERATION) at 20 percent power when a shutdown was commenced in accordance with Technical Specification 3.8.3.1 due to an inoperable inverter. The inverter powers a 400 amp bus which supplies power to portions of the Plane Protection System (PPS),

the Engineered Safety Features (ESF) Actuation System, and various plant instrumentation.

At 1532 on May 9, 1987, a fuse had blown on the "C" train inverter. The control room operators declared the inverter inoperable and entered the ACTION for Technical Specification 3.8.3.1.

During troubleshooting the inverter fuse blew again, and its associated static transfer switch did not switch power to the bus from a backup 120 volt alternating current supply. This caused the bus to lose power, which resulted in several single channel ESF and PPS trips being generated which is per design.

No ESF or PPS actuations occurred.

The root cause of the inoperable iirverter was determined to be a loose Silicon Controlled Rectifier (SCR). As corrective action the loose SCR was replaced and several other SCRs were retorqued.

No similar events have been reported previously.

870b 1 ho'395 870b08 PDR ADOCK 05000529 NRC form See S

NRC Form 3$ SA 19831 U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPAOVEO OM8 NO 3150 0101 EXPIRESI SI31/88 FACILI'TY NAME 111 OOCKET NUMSER 131 LER NUMSER lel ~ AGE ISI SSGVENTIAL ASVISION NVM NVMSSA Palo Verde Unit TEXT IIF ImNO SOoco 2

II IOOcwed. vw aAfecnV IYIICFonII 38SATI Illl 0 5 0 0 0 5 8 7 013 00 02 oFO 3 At approximately 1532 on May 10, 1987 Palo Verde Unit 2 was in Mode 1 (POWER

'PERATION) at 20 percent power when the control room operators (utility-licensed) commenced a Unit shutdown in accordance with Technical Specification 3.8.3.1 due to an inoperable inverter (EF). The inverter converts class 1E 125 Volt direct current (d.c.) power to alternating current (a.c.).

The inverter powers a 400 amp bus which supplies power to portions of the Plant Protection System (JC), the Engineered Safety Features (ESF) Actuation System (JE), and various plant instrumentation. The inverter (model f/INV 253-1-101) is manufactured by ELGAR.

At 1532 on May 9, 1987 a fuse had blown on the "C" train inverter. The control room operators declared the inverter inoperable and entered the ACTION Statement for Technical Specification (T.S.) 3.8.3.1. T.S. 3.8.3.1 requires that the associated inverter be reconnected to the Vital bus within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or that the Unit be in HOT STANDBY in the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and 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 />. The inverter cEluld not be reconnected within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and at 1532 on May 10, 1987 a Unit shutdown and sl.bsequent cooldown was commenced.

As immediate corrective action the blown fuse was replaced and attempts were made to restart the inverter. The fuse blew again, and its associated static transfer switch did not switch power to the bus from a backup 120 volt alternating current supply. This caused the bus to lose power, which resulted in several single channel PPS and ESF trips being generated which is per design.

No ESF or PPS actuations occurred.

Troubleshooting of the inverter was conducted in accordance with approved plant procedures, and revealed that 9 Silicon Controlled Rectifiers (SCRs) were found shorted. The SCRs were replaced. Attempts to r~energize the inverter caused the fuse to blow agar.n. A retest of the SCRs was conducted and inspection of all a.c. output cxrcuitry components was performed. The a.c. output circuitry components checked satisfactorily. Shorted SCRs were replaced along with SCRs that exhibited current leakage from cathode to gate to ensure that the best matched manufactured SCRs were installed in the inverter.

The SCR connections and mountings were checked. Several SCRs were found loose and were retightened. The cause of the loose SCRs could not be determined. The SCRs could have been torqued improperly during manufacturing or installation at the plant.

The inverter was restarted and the SCR firing waveforms were verified to be in accordance with the waveforms depicted in the inverter technical manual. After inverter startup, approximately 15 transfers from the inverter to regulator and back to the inverter were initiated at various load conditions to demonstrate operability. Both manual and simulated inverter fault condition transfers NIIC IIIIIM3SSA I9 83>

NRC form 3SSA U.S. NUCLEAR REGULATORY COMMISSION

)883)

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION APPAOVEO OMS NO 3150M)04 EXPIRES: 8/31/88 FACILITY NAME )) I OOCKET NVMSE)l (3)

LER NUMSE)l IS) PAGE )3)

YEAR .'8' SKOUENT/AL ym oEvrslorr rrUM e/I ~ n rrUMOTA Palo Verde Unit 2

'tEXT I// mone eoeco N ooqeeio/I, oee ereoee'one/ I/RC Fonrrr 38/rA 'el I ) 3) 0 5 0 0 0 5 2 9 8 7 013 0 0 0 3 oF 0 3 were initiated to verify inverter performance to specifications. The inverter was placed back in service at 0115 on May 14, 1987. The inverter was inoperable for approximately 4 days and 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />.

The root cause of the fuse failure has been isolated to one SCR mounted loosely in the heatsink on the middle bridge and SCRs that were not mounted in accordance with specifications. This caused misfiring and overheating of the SCRs which accounted for the premature failures. A misfiring SCR on the middle bridge can cause fuse failure on the upper or middle bridges. All Unit 2 fuse failures have occurred on the upper and middle briage of the "C" inverter.

Based on the fact that fuse failures were only occurring on the "C" train inverter it is believed that the loose SCRs are isolated to the "C" inverter.

The problems experienced in Unit 2 were evaluated for applicability to Units 1 and 3. This is an ongoing effort and corrective actions will be instituted as necessary.

Testing was conducted on the static transfer switch associated with the inverter. The loss of power to the 400 amp bus as a result of trying to make a power transfer from the regulator to the inverter could not be repeated.

Numerous attempts to recreate the loss of power were unsuccessful.

During troubleshooting it was also discovered that a wire had a resistance from termination to termination of 2.56 ohms. Since the jumper was for a common circuit it is possible that the resistance may have caused all of the static switch SCRs to turn off at once. This can result when the logic board, control board, and drive board do not communicate with each other. This can also happen when these boards are not referenced to the same common circuit.

The jumper was replaced and resistance measurements taken to ensure that all boards were referenced to the same common circu't.

I)then the PPS bus lost power single channel trips occurred as designed. The other 3 channels of PPS were still operable and were able to perform their intended function as needed. Therefore this event had t)o impact on the safe operation of the plant.

There were no structures, components, or systems inoperable at the start of the event other than as described above that contributed to the event. No failed components other than those described above affected the event.

No previous similar events have been reported. Should other concerns or information pertinent to this even't be discovered, a supplement to this report will be issued.

NRC e Oe)M 3OOA (083/

Arizona Nuclear Power Project P.O. BOX 52034 ~ PHOENIX, ARIZONA 85072-2034 192-00225-JGH/TRB/JHT June 8, 1987 Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 2 Docket No. 50-529 Licensee Event Report 2-87-013 File: 87-020-404

Dear Sirs:

Attached please find Licensee Event Report (LER) No. 2-87-013 prepared and submitted pursuant to 10CFR 50.73. In accordance with 10CFR 50.73(d), we are herewith forwarding a copy of the LER to the Regional Administrator of the Region V Office.

If you have'any questions, please contact T. R. Bradish, Compliance Supervisor at (602) 932-5300, Ext. 6936.

Very tru y yours, J. G. Haynes Vice President Nuclear Production JGH/JHT/cld Attachment Cco 0. M. DeMichele (all w/a)

E. E. Van Brunt, Jr.

J. B. Martin R. P. Zimmerman R. C. Sorenson E. A. Licitra A. C. Gehr INPO Records Center

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