05000338/LER-1981-038-03, /03L-0:on 810517,nuclear Instrumentation Power Range Channel N-44 Was Placed in Tripped Condition Due to Drifting Upper & Lower Detector Currents.Cause Unknown. Detector N-44 Rescaled

/03L-0:on 810517,nuclear Instrumentation Power Range Channel N-44 Was Placed in Tripped Condition Due to Drifting Upper & Lower Detector Currents.Cause Unknown. Detector N-44 Rescaled

ML20004F671
Person / Time
Site:	North Anna
Issue date:	06/15/1981
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML20004F670	List: 05000338/LER-1981-038, Forwards LER 81-038/03L-0 05000338/LER-1981-038-03, /03L-0:on 810517,nuclear Instrumentation Power Range Channel N-44 Was Placed in Tripped Condition Due to Drifting Upper & Lower Detector Currents.Cause Unknown. Detector N-44 Rescaled
References
LER-81-038-03L-01, LER-81-38-3L-1, NUDOCS 8106220018
Download: ML20004F671 (3)

LER-1981-038, /03L-0:on 810517,nuclear Instrumentation Power Range Channel N-44 Was Placed in Tripped Condition Due to Drifting Upper & Lower Detector Currents.Cause Unknown. Detector N-44 Rescaled

Event date:
Report date:
3381981038R03 - NRC Website

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O U.S. NUCLEAR REGULATORY COMMISSION LICENSEE EVENT REPORT CONTROL BLOCK / / / / /'/'/ (1)

(PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

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/V/A/N/A/S/1/ (2)

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• / / / (5) e LICENSEE CODE LICENSE NUMBER LICENSE TYPE CAT

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/ O 6/1/ 5/ 8/1/ (9)

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SO DOCKET NUMBER EVENT DATE REPORT DATE EVENT DESCRIPTION AND PROBABLE CONSEQUENCES (10) i

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/__On May 17, 1981, during 100% power operation, nuclear instrumentation power range /

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/, channel N-44 was placed in the tripped condition due to drifting of both upper

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/ and lowerjetecto; currents. The following day, personnel failed to use the mov- /

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/ able incore detector system within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to evaluate the quadrant power tilt '/

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/ ratio and the inoperable channel was bypassed for more than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for calibra- /

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/ tion of the channel. The public health and safety were not affected because

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/ redundant power range channels remained operable.

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SYSTEM

CAUSE

CAUSE COMP.

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CODE SUBCODE COMPONENT CODE SUBCODE SUBCODE

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REPORT REVISION LER/R0 EVENT YEAR REPORT NO.

CODE TYPE NO.

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ACTION FUTURE EFFECT SHUTDOWN ATTACHMENT NPRD-4 PRIME COMP. COMPONENT TAKEN ACTION ON PLANT METHOD HOURS SUBMITTED FORM SUB. SUPPLIER MANUFACTURER

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS (27)

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/ The cause of the upper and lower detector current level outputs drifting low is /

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/ unknown at this time. Both subsequent events resulted from inadequate procedur- /

/1/2/ -/ al instructions. Detector N-44 was satisfactorily rescaled using incore vs.

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/ excore axial offset data derived from full core flux mapping. Also, applicable

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/ procecures are being revised to clarify all associated requirements.

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FACILITY METHOD OF STATUS

% POWER OTHER STATUS DISCOVERY DISCOVERY DESCRIPTION (32)

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ACTIVITY CONTENT RELEASED OF RELEASE AMOUNT OF ACTIVITY (35)

LOCATION OF RELEASE (36)

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PERSONNEL EX"0SURES NUMBER.

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LOSS OF OR DAMAGE TO FACILITY (43)

TYPE DESC'lIPTION

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PUBLICITY-ISSUED DESCRIPTION (45)

NRC USE ONLY

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NAMC OF PREPARER W. R. CARTWRIGHT PHONE (703) 894-5151

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Virginia Electric and Power Company North Anna Power Station, Unit 1

. Attachment: Page 1 of 2 Docket No. 50-338 Report No. LER 81-038/031-0

Description of Event

On.May 17, 1981, while operating at 100% power, nuclear instrumenta-tion power range protection channel IV (N-44) was immediately placed in the tripped condition after being determined inoperable due to drifting of both upper and lower detector currents. The following day, personnel faile_d;to. evaluate the quadrant power tilt ratio within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> as required by T. S. 4.2.4.C, and the inoperable channel was bypassed by reinserting.the control power fuses for more than 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> (3 hrs. 44 min.) for. calibration of that channel. These events are contrary to T.S. 3.3.1.1 and reportable pursuant to T.S. 6.9.1.9.b.

Probable Consequences of Occurrence Fottr power range channels provide redundant monitoring of the

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reactor power level over a range of 0 to 120% full power. These channels-provide a high neutron flux reactor trip when two of the four power i.use shouuel. casced the-Leip scupotur-(set.at approximately 108 percent

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power). The channels also provide neutron flux rate trips which trip

'the reactor when an abnormal rate of increase or decrease in nuclear power occurs in two out of four channels. Because all three redundant power-range channels (channels I, II, and III) remained operable at all times to trip the reactor if required, the public health and safety were not affected.

Cause of Event

It is not known at this time what caused the upper and lower detector

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current level outputs to drift low. The quadrant power tilt ratio was not evaluated using the movable incore detector system within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of declaring the power range channel inoperable because the applicable Procedure did not properly reference this requirement. Additionally during repair, the channel was bypassed for more than two hours because the Action Statement did not specifically address how long the inoperable i

channel could be bypassed to allow calibration of the affected channel, only how long it could be bypassed for surveillance testing of redundant channels (2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) which was felt did not apply.

Immediate Corrective Action

Power range channel N-44 was satisfactorily calibrated using new incere vs. excore axial offset data derived from several full core flux maps.

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Attachment: - Page 2 of 2 Scheduled Corrective Act. ion Procedures will.be revised July 1, 1981.

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Actions Taken'to Prevent Recurrence

N,o further actions are required.

Generic-Implications There are no generic implications associated with this event.

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