ML19308A980

RO 269/77-14:on 761027,while Unit Was Being Brought to Power Operation After Maint Shutdown,Plant Computer Indicated Nuclear Instrumentation Channel Power Values Less than Heat Balance by Varying Degrees.Caused by Lack of Calibr

ML19308A980
Person / Time
Site:	Oconee
Issue date:	05/04/1977
From:	Parker W DUKE POWER CO.
To:
References
RO-269-77-14, NUDOCS 7912120743
Download: ML19308A980 (3)

Text

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Duke Power Company 5/4/77 Mr. Norman C. Moseley Charlotte, North Carolina DATE RECEIVED William O. Parkar, Jr. 5/11/77

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Ltr. advising of certain problems identifieli

& corrective actions conteinplated with regard i to the nuclear instrument calibration policy I and is provided as R0 269/77-14. . ... . .

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DUKE POWER COMPANY Powra Bun.ntxo

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4c2 SocTn Caracu Srazer, Cruar.oTrz, N. C. as24a w w Au o.ernaca,s. May 4, 1977 vice PersiOEnt TC.tp=ONE: Asta 704 SYtau Peoovct o=e 373-4083

, s Mr. Norman C. Moseley, Director .'

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U. S. Nuclear Regulatory Commission SI Suite 818 D 230 Peachtree Street, Northwest Y Atlanta, Georgia 30303 ,

Re: Oconee Unit Docket No. 50-269 {-

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Dear Mr. Moseley:

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.s The purpose of this letter is to advise of certain problems identified and corrective actions contemplated with regard to the nuclear instru-ment calibration policy at Oconee Nuclear Station and is provided as R0-269/77-14.

During the end-of-Cycle 1 operation of Oconee 1, in late 1974, the power range nuclear instrumentation channels (NI's) required frequent calibra-tion as a result of daily power changes between 60 and 90 percent full power. Duke Power Company requested B&W to evaluate the possibility of reducing surveillance frequency of comparison between the NI indications and heat balance power. By letter of August 19, 1976, B&W advised Duke Power Company that it would be appropriate to institute a more frequent calibration check of the NI's. Upon receipt of this recommendation, Duke Power Company reviewed the performance of the NI's for all three Oconee units. On October 14, 1976, Oconee operating procedures were revised to require NI calibration checks, and recalibration if necessary, following power changes greater than 10%FP. The technical specification on the frequency of the NI calibration checks and allowable tolerance on the calibration were deemed adequate at that time.

On March 25, 1977, B&W informed Duke Power Company that additional requirements should be placed on the NI calibration policy. Duke Power Company representatives met with B&W representatives on April 5, 1977 to discuss a possible course of action. Following the Duke-B&W meeting, a detailed review consisting of comparisons of NI indications and heat bale.:re power was performed to quantify the extent of mismatch between the NI's and indicated heat balance p,ower. As a result of this review, at least one instance was identified in which a significant mismatch had y occurred between the NI power and the indicated heat balance power.

.a The subj ect incident, identified on April 20, 1977, occurred on Oconee 1 on October 27, 1976 while the unit was being brought to power operation after a maintenance shutdown. The hourly plant system data logged by 771 M01oa

Mr. Norman C. Moccisy May 4, 1977 Page 2 the plant computer showed that the indicated NI power, values were less than the indicated heat balance by varying degrees, as much as 13.6%,

when reactor operation was between 50%FP and 90%FP for a period of approximately four hours. The plant computer data also indicated that the NI power values were conservative or in agreement with the indicated heat balance power at power levels below 50%FP and at power levels above 90%FP. Although the indicated heat balance power is not sufficiently accurate during period of power change, the power changes during the period in question were gradual, and therefore, the indicated mismatch between the NI power and heat balance power occurred as a result of the NI's going out of calibration.

The operation of the unit with the NI's out of calibration possibly resulted in operation of the unit with the measurement tolerance of the NI detectors being greater than the measurement tolerance for these detectors assumed in the safety analyses and in the Technical Specitica-tion bases of the RPS setpoints for 2 pe iod of approximately four hours.

Since the reactor was being operated onl, between 50%FP and 90%FP (and not close to rated power) when the NI channels were out of calibration and considering that there are significant conservatisms built into the design analysis, it is considered that this incident did not affect the health and safety of the public.

The current Oconee Nuclear Station Technical Specification requires that a calibration check be performed on the NI's once per day and that a calibration be performed if the check indicates the NI power to defer from the steady state heat balance power by 1 2% FP. A request to change the Technical Specification on the frequency of the calibration chech from once per day to once per shif t and to require recalibration only if the NI power indication is less than the steady state heat balance power by more than 2%FP is in preparation. (The existing require-ment necessitates recalibration of the NI's even when the NI calibrations are conservative). Subsequent to issuance of this technical specification change, the station operating procedures (for all three units) will be revised to require NI calibration checks and recalibrations, if necessary, following significant changes in core conditions which affect the NI flux.

It is expected that the proposed Technical Specification change supple-mented by the aforementioned procedural change would minimize the possi-

' bility of any undesirable NI calibration conditions.

Very truly yours, N L v- 0.

William O. Parker, Jr.

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