ML20083Q818

AO 73-11-10:on 731110,reactor low-low Water Level Switch Setting Found to Actuate Above Normal Setpoint.Caused by Setpoint Drift.Switch Recalibr

ML20083Q818
Person / Time
Site:	Nine Mile Point
Issue date:	11/19/1973
From:	Schneider R NIAGARA MOHAWK POWER CORP.
To:	Skovholt D US ATOMIC ENERGY COMMISSION (AEC)
Shared Package
ML20083Q821	List: ML20083Q818 ML20083Q822
References
8423, AO-73-11-10, NUDOCS 8303140647
Download: ML20083Q818 (2)

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NIAGARA MOHAWK POWER CORPORATION NIAGARA MOHAWK 300 ERIC DOULEVARO wCST SYAACUSE,N Y 432C2 November 19, 1973 2 3 Mr. Donald J. Skovholt 9 Assistant Director for Reactor Operations $UOp O[gT8' Division of Reactor Lice.nsing g OO United States Atomic F.nergy Commission , ; s b bed Washington, D. C. 20543 g k 4+

Dear Mr. Skovholt:

Ol S RE: Provisional Operating License: DPR-17 Docket No.: 50-220 This is to report a condition relating to the operation of the Nine Mile Point Nuclear Station Unit 1 in which on November 10, 1973 at 1509 hours0.0175 days <br />0.419 hours <br />0.0025 weeks <br />5.741745e-4 months <br /> a reactor low-low water 1cvel switch setting was found to actuate above the normal set point, which is allowable by Technical Specifications, but beyond the deviations as established in the basis for that specification. This condition was related to Region I Compliance by telephone and cn November 12, 1973 byphotocopyat1508 pours. .

During routine surveillance testing of the reactor low-low water 1cvel sensors (at 90*4 rated power) tae set point of one of the Yarway sensors (RE02D) was found 'to have drifted to 4' 9" below minimum normal water level. A change of three (3) inches from the last inspection on October 13, 1973 at which time the sensor tripped as required at five (5) feet below minimum normal water level.

The basis of Technical Specification 3.6.2 call for a deviation of no more than 2.6".

The purpose of the sensor is to detect decreasing reactor water level and upon reaching a level of five (5) feet below minimum normal water level or higher, a Pri-mary Coolant Isolation, Containment Isolation, Emergency Cooling Initiation and Start Core Spray Pumps permissive signal is initiated. Also, if high drywell pressure permissive signal is present, containment spray initiates. The electrical arrangement for the permissive logic is a one out of two in each trip system. It would require two sensors, one in each trip system, actuating higher than prescribed' deviations to give a permissive start of those systems above the five (5) foot level.

Ilad plant conditions required the use of any of these mentioned safeguard systems they would have actuated at the five (5) foot icvel below minimum normal. Ilowever, since the set point of RE02D was three (3) inches high it would have initiated a per-uissive signal for trip system 12 at 4' 9" below minimum normal water level instead of five (5) foot below minimum normal water level. When water level reached the five (5) foot level, the other trip system would actuate causing the safeguard systems mentioned to function.' ,

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Nty:mbcr 19, 1973 My'.' Dbnald J. .Skovholt Page 2

'U..S. Atomic Energy Commission l

The safety of the plant and general public was not jeopardized as the required systems would have functioned at the design set point.

f The imnediate corrective action was to recalibrate the sensor to read five (5)~

L foot below minimum normal water level.- The other three sensors all actuated at five

l. (5) foot below minimum normal water level.

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This is the first known malfunction of this type on this instrument. However, I it will be closely watched for any further deviation and if a trend is established further corrective action will be taken.

l Very truly yours, l

Original signed by l

' R. R. Schneider l

R. R. Schneider Vice President - Electrical Operations i

RRS:pw REGISTERED MAIL RETURN RECEIPT REQUEST I

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