ML20045D720

LER 93-009-00:on 930524,apparent Spurious Signal from Pressurizer Level Instrumentation Caused Backup Charging Pumps to Automatically Start,Due to Deterioration of Wiring. Instrument Loop Calibration Will Be performed.W/930622 Ltr

ML20045D720
Person / Time
Site:	Fort Calhoun
Issue date:	06/22/1993
From:	Gates W, Chutima Taylor OMAHA PUBLIC POWER DISTRICT
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-93-009, LER-93-9, LIC-93-0164, LIC-93-164, NUDOCS 9306290348
Download: ML20045D720 (5)

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r5?E hypF5MsFP58%vm$haine Bb2ii ...abiidlnid Lcswashuddsmn!$1M$dhAdad@sd.hEdEm?WReemWFM5F91W Omaha Pub!!c Power District P.O. Box 399 Hwy. 75 - North of Ft Calhoun Fort Calhoun, NE 68023-0399 402./636-2000 June 22, 1993 LIC-93-0164 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Mail Station P1-137 Washington, DC 20555

Reference:

Docket No. 50-285 Gentlemen:

Subject:

Licensee Event Report 93-009 for the Fort Calhoun Station Please find attached Licensee Event Report 93-009 dated June 22, 1993. This report is being submitted pursuant to 10 CFR 50.73(a)(2)(iv). If you should have any questions, please contact me.

Sincerely, if V'. h. #

W. G. Gates Vice President WGG/jrg Attachment c: J. L. Milhoan, NRC Regional Administrator, Region IV S. D. Bloom, NRC Project Manager R. P. Mullikin, NRC Senior Resident Inspector INP0 Records Center L8005u <

455'29 9306290348 930622 .

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NRC tORM 386 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 3150 o104 IW) EXPIRES 5/31/95 ESTIMATED DURDEN PER RESPONSE TO COMPLY WTH THIS o

UCENSEE EVENT REPORT (LER) g y n, % c7 % "Ac y g g yo ,"gy ,j no",b^ao AND RECORDS MANAGEMENT BRANOH PANIB 7714), U.S. NUCLEAR FIEGULATOFW COMMISSION, WASHINGTON, LC 205550001, AND TO (See reverse for required number of digits / characters for each block) d NENT D AS FACIUTV NAME (1) DOCIET NUMBER R PAGE R Fort Calhoun Station Unit No. 1 05000285 1 OF 4 Tms a Automatic Start of Backup Charging Pumps and Isolation of Letdown Flow EVENT DATE (5) LER NUMBER (6) REPORT NUMBER (7) OTHER FAC! lines INVOLVED (8) uoNm DAY YEAR YEAR MONTH DAY YEAR N R 05 24 93 93 --

009 --

00 06 22 93 '39 000 l OPERATING THIS REPORT IS SUBMITTED PURSUANT TO THE REQU!REMENTS OF to CFR 8: (Check one or more) (11) 1 X 73.71(b)

[ MODE (9) 20.402(b) 20.405(c) 50.73(a)(2)(lv) gq)WER 20.405(a)(1)(1) 50.36(c)(1) 50.73(a)(2)(v) 73.71(c)

LEVEL (10) 100 20 405(a)(imn 50.36(c)(2) 50.73(a)(2)(vil) OTHER ,

50.73(a)(2)(i) 50.73(a)(2)(viii)(A) (sperty in Ateact 20.405(a)(1)(iii)

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20.405(a)(1)(iv) 50.73(a)(2)(ii) 50.73(a)(2)(vill)(B) 20.405(a)(1)(v) 50,73(a)(2)(iii) 50.73(a)(2)(x)

UCENSEE CONTACT FOR THIS LER (12)

NAME TEt.EPHONE NUMBER (include Area Code)

Calvin C. Taylor, Shift Technical Advisor (402) 533-6754 COMPLETE ONE UNE FOR EACH COMPONENT FAILURE DESCRIBED IN THIS REPORT (13) cAuSE SYSTEM COMPONENT MANUFACTURER CAUSE SYSTEM COMPONENT MANUFACTURER PRDS "0"* U^* *E*"

SUPPLEMENTAL REPORT EXPECTED (14) EXPECTED Yta SUBMISSION pt yes, complete EXPECTED SUOMISSION DATE) X No DATE (15)

ASSTRACT (Umit to 1400 spaces, i.e., approximately 15 single-spaced typewritten lines) (16)

At 2015 CDT on May 24, 1993, with the Fort Calhoun Station operating at 100% power (Mode 1), an apparent spurious signal from pressurizer level instrumentation (LC-101X) caused both backup charging pumps (CH-1A and CH-18) to automatically start. Both backup charging pumps are designed to start when actual pressurizer level drops below programmed level by more than three percent. Immediate and subsequent investigations indicated no such deviation existed. Letdown Isolation Valve HCV-204 subsequently l closed automatically due to letdown pressure oscillations. Volume control tank and pressurizer level response was normal for the increased charging flow transient.

Deterioration of wiring in LC-101X is suspected to have caused the start signal.

A Maintenance Work Order has been initiated to inspect the wiring connections on LC-101X and an instrument loop calibration will be performed.

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NRo FORM 306A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 315o4104 I per) EXPlRE8 5/31/95 1 EORMYAON RM SO ORW -l LICENSEE EVENT REPORT (LER)

TEXT CONTINUATION AN C NAO MENT B U S NUCLE U"FArcS"rEEr@N ,"rE'cTN*o"$ Sr^c"e 5 MMMOLMENT AND BUDGET, WASHINGTON.DC 20503. l FACEJTY NAME (f) 000 NET NUMBER M LER NUMBER M PAGE M ' ,

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• E8e7 EsE Fort Calhoun Station Unit No. 1 05000285 2OF4 un m. . ..o .ao- a NRC em cm BACKGROUND The Fort Calhoun Station (FCS) Chemical and Volume Control System (CVCS) is designed to  :

perform several functions, including maintaining the reactor coolant volume within '

programmed limits. The CVCS includes three positive displacement charging pumps (CH-1A, '

'CH-1B and CH-1C).

During normal operation, level instrumentation (LC-101X or LC-101Y) on the pressurizer automatically controls the volume of water in the Reactor Coolant' System (RCS) by automatic control of the letdown flow rate and varying the number of operating charging pumps. Ordinarily, one charging pump is running to return purification flow to'the RCS, j and the other two pumps are available in standby to start on a low or decreasing pressurizer level.

In addition to its functions during normal-operations, the FCS-Updated Safety Analysis Report (USAR) classifies the CVCS as an Engineered Safety Features (ESF) System. In the event of a Pressurizer Pressure Low Signal (PPLS) or a Containment Pressure High Signal-(CPHS), a Safety Injection Actuat;on Signal (SIAS) is generated-which, in part, starts all three charging pumps to inject concentrated boric acid into the RCS. The SIAS also ,

transfers the charging pump suction from the volume control tank to the discharge of the l boric acid pumps. If the boric acid pumps are not operable, boric acid flows by gravity -I from the concentrated boric acid tank to the charging pump suction header. l The normal operation level control function of the CVCS, and emergency charging pump j start on SIAS, are independent of each other. i EVENT DESCRIPTION At 2015 CDT on May 24, 1993, withFCSoperatingat100% power (Mode 1),anapparent spurioussignalfromLC-101Xcausedbothbackupchargingpumps(CH-1AandCH-1B)to- j automatically start. Both backup charging pumps are designed to start when actual pressurizer level drops below programmed level by more than three percent. Immediate and subsequent investigations indicated no such deviation existed.

CVCS Letdown Pressure Controller PIC-210, while in automatic, began to oscillate in response to the increased charging and letdown flow. The Licensed Operator monitoring pressurizer level was about to take manual control of Letdown Isolation Valve HCV-204,.

when it closed automatically due to letdown pressure oscillations. This is an automatic protective feature to protect downstream CVCS piping. The two backup charging pumps .

automatically stopped, one at a time, as the programmed level deviation signal-from 'i LC-101X returned to normal. i NRC FORM 366A $02) -

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i NRC FORM 306A U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB NO. 315o4104 )

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YEAR NUMBER NUMBER Fort Calhoun Station Unit No. 1 05000285 93 -- 009 -- 00 TEXT (W more space is mquued, use additional copies of NFC Form 300A) (17) l The duration of the event was approximately five minutes. Volume control tank and pressurizer level response was normal for the increased charging flow transient. .

Control Room operators continued to monitor X-channel pressurizer level instrumentation,  !

and were prepared to switch to the Y-channel of the pressurizer level controller if the '

problem repeated itself.

Initial review of the event concluded that a four-hour report, pursuant to 10 CFR 50.72(b)(2)(ii) was not required because the equipment was not started by an ESF signal and because the signal was invalid. However, followup review resulted in a decision to report the event The NRC was notified of the event pursuant to 10 CFR 50.72(b)(2)(ii) on Ma 25, 1993 at 1407 CDT. This report is being submitted pursuant to 10 CFR 50.73(a)( )(iv).

SAFETY ASSESSMENT This event posed no threat to nuclear safety as the charging pumps performed as required for a level deviation signal, albeit invalid. Letdown flow isolation was as required for the high letdown back pressure condition.

CONCLUSIONS Deterioration of wiring in LC-101X is suspected to have caused the start signal.

CORRECTIVE ACTIONS The following corrective actions will be completed:

1. A Maintenance Work Order (MW0) has been initiated to inspect the wiring connections on LC-101X. Due to the sensitive nature of the connections and possible degradation of the wiring, the work will be performed during the next refueling outage.

2. Although the instrument loop is presently functioning as designed, a full instrument loop calibration will be performed during the next refueling outage, in an effort to determine the source of the system perturbation.

3. Available guidance for determining reportability of ESF actuations will be reviewed to assess whether adequate information is readily available to appropriate perscnnel. This review will be completed by July 31, 1993.

1 NC FORM 3MA @e2)

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NRC FORM 306A U.S. NUCLEAR RE1ULATORY COMMISSION APr ROVED BY OMB NO. 31504104 pea) EXPlRES 5/31/95

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UCENSEE EVENT REPORT (LER) E ATE O W E'NF TDCT CONTINUATION AND RECORDS MANAGEMENT BRANCH (MNDD 7714), U.8, NUCLEAR FIEGULATORY COMMISSON, WASHINGTON, DC 20$$64001, AND TO THE PAPERWORK REDUCTON PRCMECT (31504104), OFFCE OF MANAGEMENT AND BUDGET, WASHING 1DN,DC 20503.

FACKJTY NAME (1) DOCMET NUMBER R LIR NUMBER M PAGE(14 g SEQUENTIAL REVISON NUMBER NUMBER Fort Calhoun Station Unit No. 1 05000285 93 --

009 -- 00 TExr p - c. N ,.au,,.o o.. .aoinort.i , NRC r ,m 3e6A) (17)

PREVIOUS SIMILAR EVENTS No previous similar events, involving an invalid automatic start of charging pumps during normal operation, have been reported.

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NAC FORM 306A (542)