ML19312C902

Forwards LER 78-004/01T-0

ML19312C902
Person / Time
Site:	Oconee
Issue date:	04/17/1978
From:	Parker W DUKE POWER CO.
To:	James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19312C903	List: ML19312C902 ML19312C904
References
NUDOCS 8001130237
Download: ML19312C902 (4)

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April 17, 1978 Mr. James P. O'Reilly, Director U. S. Nuclear Regulatory Commission ei sj Suite 1217 'd 230 Peachtree Street, Northwest Atlanta, CA 30303 -

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Occaec Unit 2 ri  :: :J Docket No. 50-270 o.

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Dear Mr. O'Reilly:

Pursuant to Sections 6.2 and 6.6.2 of the Oconee Nuc1 car Station Technical Specifications, please find attached Reportable Occurrence Report R0-270/78-4.

Very truly yours,

<14sa C&f f6(/

William O. Parker, Jr.

Q PMA/vmb Attachment A cc: Director, Office of Management Information

' and Program Control

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DUKE PONER COMPANY OCONEE UNIT 2 Report Number: R0-270/78-4 Report,Date:

o Apt il 17,1978 March 23, 1978 Occurrence Date:

Facili ty_:

Oconce Unit 2, Seneca, South Carolina Nuclear Instrumentation Out-of-Calibration Identification of Occurrence:

88 Percen: Full Power Conditions Prior to Occurrence:

Description of Occurrence:

tion (NI)

As the result of a review of the data pertaining to Nuclear Instrumenta2 for the pe power range channel readings of Oconee Unitin two instances, the NI power indications March 1, 1978, it was determined that h l t computer by a were less than the thermal power values (calculated by t e p tan f 4% to 5%.

combination of primary and secondary heat balances) by amoun s o Unit 1.

Further investigation revealed that two similar instances occurred diatelyon The non-conservative NI power indications occurred during less than fullimme and/or h

following power increases and while reactor power. h operation was atIn in two hours of exceeding a 4% NI thermal power mismatc .

Apparent Cause of occurrence _: s b i The apparent cause of this occurrence is the NI's drif ting out-of-cali in power level. rat on a result of changes in core characteristics accompanying changes Analysis of Occurrence _:

d to The N1 channels are part of the Reactor Protection System (RPS), i require d

initiate reactor trips during transient or off-normal events when The analyses of the trip setpoints and the mon tore f ed assuming a parameter exceeds the trip setpoint.the safety Therefore, analyses the incident of postulated measurement tolerance of 4% for the NI detectors. hours with h

resulted in operation of Units 1 and However, 2 for athe period of less safety analyses than t N1 measurement tion that saf ety analyses and RPS trip setpoint analyses.and RCS flow, RCSRPS pres- trip se several other independent parameters or pnenomena area,asfuel rod and pellet channel flow(such l l at sure and temperature, power peaking, hotcharacteristics, re assumed calculati their worst design values; and further, the monitored parameters weTherefore, all these to be measured with the maximum design tolerance. l during meters would have to be simultaneously at their worst design va ues

t r.mnlent s for the enre safety limits to be approached. Recognizing that the j

N1'r. w"re out of the required calibratton tolerance only for a short period of tine, that the calibration tolerance was exceeded at power icvels less than conservatisms, it is full power, and that design analyses include significant considered that this incident did not pose a significant threat to the health and safety of the public.

Corrective Actions:

Instances of NI's being out of calibration have been previously identified at Oconee Nuclear Station as reported in R0-269/77-4, and certain corrective actions were in.plemented at that time. These corrective actions have been ef fect ive in reducing the number of such occurrences. To further minimize the following addi-the possibility of undesirable NI calibration conditions, I

tional corrective actions have been implemented:

1. During unit startups, a 3% to 5% conservatively biased calibration will be applied to the NI power range channels at 30% FP.

2. During power increases, if the thermal power . exceeds the NI indication by

' 2%, the power increase will be temporarily halted and the NI's appropri-ately adjusted (e.g. , a 3% to 5% conservative bias applied).

3. The Limits and Precautions sections of applicable operating procedures will be revised to include a caution statement not to exceed a non-conserva-tive NI calibration error of 4.0%.

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