ML17303A743

LER 87-004-00:on 871217,w/reactor at 50% Test Plateau During Power Ascension Testing,Reactor Trip Occurred.Caused by Malfunctioning Logic Sequencer Card in Control Element Drive Mechanism Control Sys.Card replaced.W/880115 Ltr

ML17303A743
Person / Time
Site:	Palo Verde
Issue date:	01/15/1988
From:	Haynes J, Shriver T ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
192-00336-JGH-T, 192-336-JGH-T, LER-87-004-02, LER-87-4-2, NUDOCS 8801200197
Download: ML17303A743 (12)

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REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:8801200197 DOC.DATE: 88/01/15 NOTARIZED: NO DOCKET FACIL:STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH. NAME AUTHOR AFFILIATION SHRIVER,T.D. Arizona Nuclear Power Project (formerly Arizona Public Serv HAYNES,J.G. Arizona Nuclear Power Project (formerly Arizona Public Serv RECIP.NAME RECIPIENT AFFILIATION

SUBJECT:

LER 87-004-00:on 871217,reactor trip

. element assembly subgroup deviation.

occurs due to control R

W/8 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR / ENCL Q SIZE: 1 TITLE: 50.73 Licensee Event Report (LER), Incident Rpt, etc. D NOTES:Standardized plant. 05000530' RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 A LICITRA,E 1 1 DAVIS,M 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 AEOD/DOA 1 1 AEOD/DSP/NAS 1 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 1 ARM/DCTS/DAB 1 1 DEDRO 1 1 NRR/DEST/ADS 1 0 NRR/DEST/CEB 1 1 NRR/DEST/ELB 1 1 NRR/DEST/ICSB 1 1' NRR/DEST/MEB- 1 1 NRR/DEST/MTB 1 NRR/DEST/PSB 1 1 NRR/DEST/RSB 1 1 NRR/DEST/SGB 1 1 NRR/DLPQ/HFB 1 1 NRR/DLPQ/QAB 1 1 NRR/DOEA/EAB 1 1 NRR/DREP/RAB 1 1 NRR/DREP/RPB 2 2 NRR- /SIB 1 1 NRR/PMAS/ILRB 1 1 G FI 02 1 1 RES TELFORD,J 1 1 S/.DE/E 1 1 RES/DRPS DIR 1 1 RGN5 FILE 01 1 1 EXTERNAL: EG&G GROH, M' 5 5 FORD BLDG HOY,A 1 1 ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC HARRIS,J 1 1 NSIC MAYS,G 1 1 NOTES 1 1 A

TOTAL NUMBER OF COPIES REQUIRED: LTTR 48 ENCL 47

0

0, NRC Forrr! 848A U.S. NUCLEAR REGULATORY COMMISSION 18851 LICENSEE EVENT REPORT {LER) TEXT CONTINUATION APPROVEO OMS NO 5150MI04 EXPIRES: 8/31/88 FACILITY NAME Ill DOCKET NUMSER LTI LER NUMSER LS) PACE IS) 5EOUENT/AL rrN /IS v/5 ro rr

'0 400,02or.

HI/M 5/I r4r rrI/MFSA Palo Verde Unit 3 o 5 o o o 5 3 8 7 0 4 TEXT /// rrrrrrP 54444!8 te lrr/rr/L I/FP rddPo'end A!/TC F4rrrrr 8/R/A8/ (LTl On December 17, 1987 at approximately 0430 IIST, Palo .Verde Unit .3 was in Node 1 (POWER OPERATION) at approximately 50K reactor .(RX) power when a reactor trip occurred due to a Low Departure from Nucleate Boiling Ratio (DNBR) trip signal. The DNBR. trip signal was generated as the result of a- deviation in position occurring between two Part Length Control Element Assembly (PLCEA)(AA) subgroups. The trip occurred during power ascension testing while the reactor was at the 5(5 test plateau. The reactor trip was uncomplicated and the plant was stabi-lized within 30 minutes terminating the event. No Engineered Safety. Features (ESF.)(JE) actuations occurred and none were required.

On December 17, 1987; Unit 3 was conducting power ascension testing per approved test procedures. Prior to the trip, testing was in progress for Control Element Assembly (CEA).(AA) shadowing,factoriradial peaking factor verification. The test required that the Part Length Control Element Assemblies (PLCEA)(AA) be inserted whi,le diluting the Reactor Coolant System (RCS)(AB) to maintain a relatively constant power level. At approximately 0427 HST with the.PLCEA's partially inserted, a number of pre-trips and trips occurred on Channel ND" of the Core Protection Calculator (CPC)(JC). A reactor trip did not occur at this time since a .reactor trip requires a two-of-four coincidence and no other channels tripped. The control room operator (utility, licensed) immediately stopped the PLCEA insertion and the trips,and pre-trips in CPC Channel ND" reset. Additionally, the reactor operators terminated the dilution of the RCS and control room (NA) personnel proceeded to investigate the cause of the Channel NDN trip signals.

Investigation by the control room operators, shift supervisor (utility, licensed), assistant shift supervisor (utility, licensed), and the reactor engineer (util.ity, non-licensed) acting, as the Test D.irector could not identify an apparent indication which would explain the CPC Channel ND" trip and subsequent reset. Concurrently, although the dilution had been terminated, a reactivity change continued due to the effects of the dilution as there is a time delay'between when the dilution is terminated and when equilibrium conditions exist. This, resulted in the average RCS temperature-continuing to rise. To stop the temperature rise, control room personnel had the choice of either adding boron to the RCS or, continuing the PLCEA insertion. Due to the fact that there was:no alarm condition indicating. an unacceptable subgroup deviat.ion in:the PLCEA's, it was decided to continue with the PLCEA insertion. Immediately following, the initiation of the PLCEA insertion, the reactor, tripped on low DNBR., The reactor'rip was determined to be uncomplicated. by the'hift supervi'sor and the plant was stabilized with'in 30 minutes terminating the event.

Except as discussed below, there were no structures, systems, or components inoperable at the start of the event which contributed to the event. There were no automatic or manual,ly initiated Engineered Safety Features (ESF)(JE) occurring during the. event and none were necessary.

'rAC r r/rrM 5444 19 85r

41 g

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NRC FoIIII 344A U,S, NUCLEAR REOULATOIIY COMMISSION 184131 LICENSEE EVENT REPORT {LER) TEXT CONTINUATION APPROVED OMS NO 3140&104 EXPIR ES: 8/31/88 FACILITY NAME 111 OOCKET NUMSER (11 LER NUMSER 14) PACE 131 FEOVENTIAL P.ot AEYISIVN NVM44 II NVMFEA Palo Verde Unit 3 o s o o o 8 7 0 0 4 00 03 OF 0 4 TEXT /// /oo/o aooco it teOuiwt. v>> PtPO 'oott HP/C Atttt 3//SA'tl 117)

Subsequent investigation into the cause of the reactor trip identified that CPC Channels NAU and "DN had initiated trip signals due to a large penalty factor being applied to the calculated values of DNBR. The penalty factors were applied to the CPC calculation of DNBR due to a CEA subgroup deviation of greater than 7.5 inches. During the sequence of events described above, it is postulated that the CEA position-sensing reed switch (33) closed and re-opened momentarily as the PLCEA's were being inserted during the testing. Since PLCEA motion was stopped due to the CPC Channel NDN trip alarms, the reed switch remained opened a llowing CPC "DN to reset. Following the determination to continue inserting PLCEA' in order to maintain temperature in the RCS, the reed switches monitoring CEA position closed in Channels NAN and NDU resulting in the large penalty factor insertion into the DNBR calculation for these channels, A review of plant conditions conducted after the trip identified that the subgroup deviation between the PLCEA's actually was greater than 7.5 inches. Therefore the Core Protection Calculator performed as designed and a reactor trip resulted. The PLCEA subgroup deviation for CPC Channels UBN and UCU were verified to be less than the 7.5 inch setpoint. Therefore Channels UBU and UCU operated as designed.

The root cause of this event was a malfunctioning Logic Sequence Card (ZC) 'in the Control Element Drive Mechanism Control System (CEDMCS)(AA). The malfunctioning card resulted in one PLCEA subgroup not consistently moving when required. This resulted in the subgroup deviation greater than 7.5 inches as discussed above. As corrective action to prevent recurrence, the Logic Sequencer Card has been replaced and CEA movement has been verified to be satisfactory. As additional corrective action, a root cause of failure analysis is being performed on the malfunctioning card.

Fo llowing the reactor trip, pressurizer (AB)(PZR) level decreased as expected; however, the class 1E pressurizer heater banks (EHTR) did not deenergize at 25K pressurizer level as required. Subsequent troubleshooting identified the root cause as a malfunctioning relay (94) and contact (CNTR) assembly in the heater control circuitry. As corrective action the relay/contact assembly has been replaced and proper heater operation verified. Also, a root cause of failure will be performed on the relay/contact assembly.

Subsequent review determined that no heater damage has occurred. Review of plant performance data following the trip indicated that the lowest pressurizer level attained was 2N. Also, the heaters were deenergized by the reactor operator when the pressurizer level reached 24K. Since 24/

pressurizer level is well above the top of the class lE heaters, no heater damage was anticipated, and no damage has been indicated through subsequent operation.

NNC IOIIM 3444 IP 83 I

NRC Focm 344A U.S. NUCLEAR REOULATORY COMMISSION IQ83)

LICENSEE EVENT REPORT {LER) TEXT CONTINUATION AFFROVEO OMS NO 3150&)04 EXFIRES: S/31/SS FACILITY NAME 111 DOCKET NUMSER 12) LER NUMSER (4) FACE 13I YEAR if' 4EOVENT/AL NVMSSA SVISKIN NVMSSA Palo Verde Unit 3 o s o o o 5 3 0 7. 0 04 00 04 oF 0 4 TEXT /1/mo/4 aooco /I /oouuocE u>> aA/4'an/4/HRC Fcum 3/E)A'c)OT)

An additional concern was identified since there is no alarm provided to warn control room personnel of an, impending reactor trip due to subgroup deviations amongst the Part Length Control Element Assemblies (PLCEA).. Based upon this concern, an engineering evaluation will be performed to evaluate a permanent change which would provide an alarm to control room personnel when subgroup deviations occur that may cause a reactor trip. Additionally, training will be conducted with control room personnel (utility, licensed) to reemphasize the fact that a reactor trip may result from excessive subgroup deviations.

Furthermore, administrative controls will be established to ensure that PLCEA subgroup deviations do not increase until penalty factors are generated.

These corrective actions will be applied to all three Palo Verde Units.

As described above, the reactor tripped as designed and all safety responses necessary to place the plant in a stable condition worked properly. There were no ESF actuations. Other than described above, there were no structures, systems, or components inoperable prior to the event which contributed to the event. There were no unusual characteristics of the work location that contributed to the event. Based upon the above, this event had no impact on the health and safety of the public.

Ho similar reactor trips have occurred.

MALFUNCTIONING COMPONENT IHFORI'1AT I OH:

Lo ic Se uencer Card Manufacture er: Electro Mechanics, Incorporated Model No.: 38311 Pressurizer Heater Contractor/Rela Assembl Manufacturer: ITE Circuit Breaker, Ltd.

Mode 1 No.: J13PA4312 NAC ~ 0AM 444A 19 SSc

ia Arizona Nuclear Power Project P.O.'OX 52034 ~ PHOENIX. ARIZONA85072-2034 192-00336-JGH/TDS/DAJ January 15, 1988 NRC Document Control Desk U .S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 3 Docket No. STN 50-530 L'icensee Event Report 87-004-00 File: 88-020-404 Attached please find Licensee Event Report (LER)'o. 87-004-00 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 quest,ions, please contact T,. D. Shriver, Compliance Manager at (602) 393-2521.

Very truly yours,

'I/l~ J~y~~-

J. G.:Haynes Vice President" Nuclear Production JGH/TDS/DAJ/kj Attachment cc: 0.. M. DeMichele (all w/a)

E. E. Van Brunt, Jr.

J. B. Martin J. R. Ball R. C. Sorenson

E. A. Licitra A..C. Gehr INPO Records Center

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