ML20006E980

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LER 90-004-00:on 900115,nuclear Instrument Power Range Channel N43 Became Inoperable Due to Power Supply Failure. Caused by Computer Program 3R5 Design Inadequacy.Night Order Issued to Enter Tech Spec 4.2.1.1.1.b.W/900214 Ltr
ML20006E980
Person / Time
Site: Millstone Dominion icon.png
Issue date: 02/14/1990
From: Mcconnell J, Scace S
NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:
NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-004, LER-90-4, MP-90-170, NUDOCS 9002270029
Download: ML20006E980 (4)
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Reference:

Facility Operating License No. NPF-49

  • Docket No. 50-423. .

Licensee Event Report 90-004-00  ;

Gentlemeni

'f This letter iorwards Licensee Event Report 90-004-00 required to be submitted withi .[

f thirty (30) days tTursuant to 10CFR50.73(a)(2)(i), any condition prohibited by the s plant'g  !

Technical Specifications. ,

Very truly yours,

~ NORTHEAST NUCLEAR. ENERGY COMPAh"f n

_ FOR: Stephen-E. Scace

' Director, Millstone Station 3.

w BY: Ha'rry F. as es L Mills' tone L ' Services ctor

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Attachment:

LER 90-004-00

-cc: .W. T. Russell, Region I Administrator W. J. Raymond, Senior Resident inspector, Millstone Unit Nos.1, 2 and 3 D. H. Jaffe, NRC Project Manager, Millstone Unit No. 3 Y09 900227002o 900214 PDR 6 ADOCK 05000423 PDC A'

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2 NRC Form 366 U.S. NUCLEAR REGULATORY COMMIS3 ION APPROVED OMB NO. 3160-0104 (6-89)' EXPAE S: 4 /30/g2 Est6msted buroen per rssponss to comply with tnis information collection recuest: 60.0 hrs. Forward ,

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LICENSEE EVENT REPORT (LER) ano neports Management Branen iv.630i. U S. Nuei.ar Ftegulatory Commission. WasNngton. DC 20666. anc to the Paperwork Reduction Prosect (3160-0104b Office of Management and Buoost. Washmoton. DC 20603 F ACiUTY NAME (t) . . .

DOCKE'l NUMBER (2) WP

  • Millstone Nuclear Power Station Unit 3 ol sl ol 01014 l213 1lOFl Ol 3 T O LE (41 Failure of Axial Flux Difference Monitor Alarm Due to inadequate Design and Procedural Inadequaev EVENT DATE (68 LFA NUMPFA (6) REPOAT DATE th OTHFA E ACiUTIES INVOLVFD IAl MONTF DAY YEAR YEAR

@ MONTH DAY YEAR FActuTY NAMES of 6l ol ol ol' l l 0 1 1l5 9 0 9 l0 0l0l4 0l 0 0l 2 1l 4 9 l0 og3;ogogog ;g OPERATING THis REPORT IS BEING SUBMITTED PURSUANT TO THE REOuiREMENTS OF 10 CFR 1: (Cneck one or more of tne foisowmgittil 20 402(b) 20 402tc) 60.73ta)(2Hwl 73.7ttb) p R 20 406(4)(110) 60.36tc)(1) 60.73laH2Hv) 73,7 tic) 10i 1l0l0 20 406(a)(1)til) 60.36(c)(2) 60.73. < a)<2)ivio _ (Ty(Ag( go,ecign, b _

20 406(a)(1HiiO g 60.73(alf2)(i) _

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UCENSEE CONTACT FOR THIS LER (121 NAME TELEPHONE NUMBER AREA CODE John W. McConnell, Engineering Technician, Ext. 5254 2l0l3 4l 4l 7l-l 1l 7l 9l 1 COMP LETE ONE UNE FOA E ACH COMPONENT F AILURE DESCR! BED IN THIS REPORT (131 CAUSE SYSTEM COMPONENT l M hgC- g g CAUSE SYSTEM COMPONENT hhk .. w\ ..\

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M NO l g l ABSTRACT (Limit to 1400 spaces. Le , approximately fifteen smgie-space typewritten hnes) (16)

On January 15,1990 at 1553, while in Mode 1, at 100G power, 586 degrees Fahrenheit, and 2250 psia, nuclear instrument power range channel N43 became inoperable due to a high voltage power supply failure.

The nuclear instrument failure made the Axial Flux Difference (AFD) Momtor Alarm, computer program 3RS, Tilting Factors inoperable. Manual logging of AFD was started on January 15,1990 at 2045, but i not within the I hour hmit as required by Technical Specification 4.2.1.1.1.b. The time between the program becoming inoperable and manual logging of AFD was approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. A review of plant data for this period shows that all AFD limits were met during this time interval and there was no significant impact on safety.

The root causes of the event were computer program 3R5 design inadequacy and procedural inadequacy which did not recognize the consequences of an inoperable power range channel on the AFD monitor alarm.

1 As short term corrective action, a Night Order was issued by the Operations Supervisor to immediately l l enter Technical Specification 4.2.1.1.1.b whenever a power range channel is inoperable. The actions to prevent reoccurrence included procedure changes to manually monitor AFD with an inoperable power range channel and pl.)nned modification to the AFD monitor alarm by June 1,1990.

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50-0104

[ - ggf o,rm 360A - U.S. NUCLE AR REGULATORY CoMMISSloN APPRovgo B N Estimated buroen per response to comply witn tNs >

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Regulatory Commission. WasNngton. DC 20655. and to i the Paperwork Reduction Proiect (3150-0104), office of

( Management and Buopet WanNnoton DC 20503 F ACILrTY NAME tt) DOCKET NUMBER (2) tFA NUueF A #s5 PAGE(3)

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1. Deerintion of Event ,

On January '15,1990 at 1553, while in h1 ode 1, at 100% power, 586 degrees Fahrenheit, and 2250 psia, nucleai instrument power range channel N43 alarmed on the alarm printer at 103.5% j power. Channel N43 was observed to be fluctuating between 100% and 108% power. Investigation

  • revealed that the high voltage power supply, which is normally set at 800 Volts-DC (VDC), was supplying 2,945 VDC. During the troubleshooting and repair of the power range channel, it was determined that the Axial Flux Difference (AFD) monitor alarm was not indicating properly and the program was inoperable. Manual logging of AFD was started on January 15,1990 at 2045, but -

not within the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> hmit as required by Technical Specification 4.2.1.1.1.b. Power range channel N43 was returned to service at 2105 on January 15, 1990. Manual loggmg of indicated AFD was terminated at 2105 on January 16. 1990.

TechniLal Specification 4.2.1.1.1.b requires that the indicated AFD for each operable excore detector be monitored and logged at least once per hour for the first 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and at least once per 30 minutes thereafter, when the AFD monitor alarm is inoperable and power is greater than 15% power.

II, Cnw of Event The root causes of the event were design and procedural inadequacy. The AFD monitor alarm was not designed to provide accurate information if a power range channel became inoperable. The Instrumentation and Control Department procedures and the alarm response for an inoperable power range channel did not require Shift Management to enter Technical Specification 4.2.1.1.1.b when greater than 15% power. '

III. Anniv* of Fvent This event is reportable pursuant to 10CFR50.73(a)(2)(i), as a condition prohibited by Technical Specifications. Manual logging of AFD was not initiated within the I hour time limit required by Technicel Specification 4.2.1.1.1.b.

The Technical Specification for AFD required that the AFD be maintained within the target band of +3% to -12% about the target flux difference for a core average accumulated burnup of greater than 3000 megawatt days per metric ton of uranium (MWD /MTU). For a core average burnup of less than 3000 MWD /MTU, the target band is 15% about the target flux difference. The safety analysis allows for a deviation of 3% between actual core AFD and indicated AFD. Operation of -

the core with indicated AFD outside of the target band is allowed between 15% and 90% power, but is limited to a cumulative penalty deviation time of I hour during the previous 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. With power grater than 90% and indicated AFD outside of the target band, AFD must be restored to within the target band or power reduced to less than 90% within 15 minutes.

A detailed review of the operation of the AFD monitor alarm showed that during potential worst case plant conditions the AFD could have been outside of its target band by as much as 4% more than what is allowed by the safety analysis, if a condition had existed where AFD was near the extreme ends of the target band (i.e., +3 or -12 from the target), a low nuclear instrument channel failure could have caused the calculated value of AFD to be reduced by as much as 4%. This would have occurred without a comparable change in the alarm setpoints. As such, the operator would have been alerted to the alarm condition late.

During the period the alarm was inoperable, plant data indicates that actual AFD remained within 0.5% of the target at all times which was well within the operating limits for AFD. The actual error introduced by the N43 failure was on the order of 0.8% versus the potenual maximum of 4%. In addition, backup instruments and recorders independent of the R5 computer program also determine AFD for the operator.

NRC Form 366A (6-60)

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tne Paperwork Amouction Proiect (3150-0104). office of Management and Bucoet. Washington. DC 20503 FACILITY NAME (t) DOCKET NJMBER (2) tro NouPER on PAGE (36 YEAR Millstone Nuclear Power Station Unit 3 - '~

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!!). Analvtic of Frent (cont.) ,

iThere have been numerous occasions when a power range instrument was inoperable due to corrective maintenance or surveillance with' power greater than 15G. During these occasions AFD should have been monitored in accordance with Technical Specification 4.2.1.1.1.b. A review of plant data and. knowledge of plant conditions indicate that at no time were Technical Specifications limits exceeded.

IV. Cerective Action Immediate corrective action was to begin manual logging of AFD in accordance with Technical Specification 4.2.1.1.1.b at 2045 on January 15, 1990. Channel N43 was repaired and the R5 i program started calculating AFD properly at 2105 on January 15, 1990.

As short term corrective action, a Night Order was issued by the Operations Supervisor to immediately enter Technical Specification 4.2.1.1.1.b whenever a power range channel is inoperable. Subsequently, the Instiument Falure Response procedure was changed to require Shift Management to enter Technical Specification 4.2.1.1.1.b when a power range instrument fails and power is greater than 15Fc.

The AFD monitor alarm program will be modified to correct for an inoperable power range detector by June 1,1990, s

Unit 3 Instrumentation and Controls Department has modified all the appropriate procedures to -

inform the operators that program R$ is inoperable when testing the power range detectors and to .i enter Technical Specification 4.2.1.1.1.b when power is greater than 15Fe.

V. Additional Infqrmation There are no similar events with the same root cause and underlying concerns. _ However, LER 66-026-00 and LER 89-029-00 document events when the R5 alarm was inoperable, but due to different root causes. In LER 86-026-00,~ the root cause was a cognitive failure of personnel to realize the computer failure rendered the AFD monitor alarm inoperable. In LER 89-029-00, the root cause was procedural inadequacy in that a software modification procedure did not specify adequate restoration guidelines. The corrective action was to provide specific procedural guidance on implementation of, and restoration from, software modifications. Therefore, the corrective actions discussed in LER 86-026-00 and 89-029-00 would not have prevented this occurrence.

Ells Codes Svetems Comnonent  ?

Computer System - ID Axial Flux Differential Monitor Alarm - ALM j incore/Excore Monitoring System - IG l

1 i NRC Form 366A (6-89) l

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