ML19256A697

LER 78-129/03L-0 on 781219: During Performance of Routine Periodic Test of Reactor Rate Trip Time Constant for Nis Channel N-42, Allowable Time Limits Were Not Observed.Caused by Electronic Drift in Instrumentation

ML19256A697
Person / Time
Site:	North Anna
Issue date:	01/03/1979
From:	Cartwright W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML19256A683	List: ML19256A682 ML19256A685 ML19256A692 ML19256A697 ML19256A701 ML19256A704
References
LER-78-129-03L, LER-78-129-3L, NUDOCS 7901090215
Download: ML19256A697 (2)

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f4 09 14 7S DAT E 1 8 8,0 ta l DOCK E T NUY H E H EVEN T UESCRSTION AND PROBABLE CONSEGUENCES h rT]T] l During pe-formance of a routine periodic test to measure the reactor " rate" trip time I o .,

constant for flIS channel fi-42, the allowable limits were not observed. The measured I g ; value of 5.57 of Rated Thermal Power with a time constant of 1.98 seconds was less _j o s [ than the Tech. Spec. requirement of >p 2 seconds, as specified in Table 2.2-1, I g lThis event is reportable under T.S. 6.9.1.9.b. Because redundant instrumentation I in ,j was available, this event did not jeopardize the health and safety of the ceneral l public. 1

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Attachment:

Page 1 of 1 Docket No. 50-338 Report No. LER 78-129/03L Description of Event:

On 12/8/78, a period test was performed to measure the rate trip time constant for NIS channel N-42. The allowable limit presented in table 2.2-1 of the North Anna Technical Specification is a >/= 2 second time constant for a </=

5.5" change in rated thermal power. The measured value for this transient was 1.98 seconds as obtained from extrapolation of the test data. This is reportable as per T.S. 6.9.1.9.b.

Probable Consequences of Occurrence:

The power range positive rate trip provides protection against rapid flux increases which are characteristic of rod ejection events from any power level, The power range negative rate trip provides protection to ensure that the minimum DNBR is maintained above 1.30 for multiple control rod drop accidents. The rate trips are obtained from outputs of the four power range detectors. These out-puts traverse 4 separate protection channels which make up a 2 of 4 "high aeutron flux rate reactor trip." Since the design basis for this protection assumes a single failure, this event would not have prevented the reactor trip or subsoquent equipment operation if orotection was required. Therefore, the health and safety of the general public was not jeopardized.

Cause of Occurrence:

This event was caused by some electronic drift in the circuitry since the previous calibration. It is not believed that this drift was excessive or required more than recalibration to correct.

Immediate Corrective Action:

The inmediate corrective action was to perform the appropriate instrument calibration procedure. The periodic test was then successfully completed.

Scheduled Corrective Action:

No further action is required.

Action Taken to Prevent Recurrence:

No further action is required.