ML19209D164

LER 79-045/03L-1:on 790330,borated Water Storage Tank Low Level Trip Setpoint in Safety Feature Actuation Sys Channel 2 Was Out of Tolerance.Caused by Noisy Constant Current Test Potentiometer.Potentiometer Replaced

ML19209D164
Person / Time
Site:	Davis Besse
Issue date:	04/25/1979
From:	Nelson J TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19209D152	List: ML19209D151 ML19209D156 ML19209D160 ML19209D164 ML19209D171
References
LER-79-045-03L, LER-79-45-3L, NUDOCS 7910190480
Download: ML19209D164 (3)

Text

U. S. NUCLEAR REGULATORY COMMISSION NRC F ORM 365 (7 773 LICENSEE EVENT REPORT (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

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CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h gj l On May 2, 1979 during Mode 5 operation, investigation under MWO IC-246-79 showed that ;

i i a noisy constant current test potentiometer located within the SFAS cabiuct was the e 1

actual cause of the bistable drif t. The potentiometer was replaced, and the bistable

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i l3lg successfully retested on May 4, 1979, under ST 5031.01, and declared operabic. l li id l I 60 7 8 9 OTHER STATUS Di CO RY DiSCOVERv OESCRipTION ST S  % PO.'.ER NA l i s @@ l 0' l 7 l 3 ' ]@ " l B l@l Surveillance Test ST 5031.01 A TIVITY CONTENT REtEASEO OFRE< EASE tOCATION oF RETE ASE @

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.Iames M. Nelson PHONE: 419-259-5000. Ext. 213{

. TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-50 DATE OF EVENT: March 30, 1979 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Borated Water Storage Tank (BWST) low level trip setpoint in Safety Features Actuation System (SFAS) Channel 2 was out of tolerance Conditions Prior to Occurrence: The unit was in Mode 1, with Power (FRTT) = 2023, and Load (Gross MWE) = 665.

Description of Occurrence: At 1045 hours0.0121 days <br />0.29 hours <br />0.00173 weeks <br />3.976225e-4 months <br /> on March 30, 1979 during the performance of Surveillance Test ST 5031.01, "SFAS Monthly Test" on SFAS Channel 2, it was found that the BWST low level trip setpoint was out of tolerance by less than one inch of BWST level.

This occurrence placed the unit in Action Statement 9 of Technical Specification 3.3.2.1. This Technical Specification states that the BWST Icvel instrument strings shall be operable while the unit is in Modes 1, 2, and 3. Action Statement 9 states that with one channel inoperable, operation may proceed provided the in-

• operable unit is placed in the tripped condition within one hour, and three other .'

channels are operable. .

Designation of Apparent Cause of Occurrence: The cause of this occurrence was 1 initially attributed to drift of the analog amplifier. However, on May 2, 1979 under Maintenance Work Order FRA) IC-246-79, investigation showed the cause to be a noisy constant current test potentiometer located within the SEAS cabinet.

Analysis of Occurrence: There was no danger to the health and safety of the public or to station personnel. The other three BWST low level instrument strings were opera-ble during the period that the setpoint for Channel 2 was out of tolerance. The set-point did not f ail completely but drif ted less than one inch of BWST level.

Corrective Action: At 1140 hours0.0132 days <br />0.317 hours <br />0.00188 weeks <br />4.3377e-4 months <br /> on March 30, 1979, the SEAS Channel 2 BWST low level trip setpoint was reset to within tolerance limits as given in Technical Specification 3.3.2.1 by performing Surveillance Test ST 5031.01. The bistable was declared operable within one hour of the initial failure. Further investigation determined the analog amplifier as a possible source of drift. On April 9, 1979, it was calibrated. On May 2, 1979 during Mode 5 operation, investigation under MWo IC-246-79 showed that a noisy constant current test potentiometer located within The potentiometer was 1 the SEAS cabinet was the actual cause of the bistable drif t. 5031.01, replaced and the bistable successfully retested on May 4,1979 under ST and' declared operable.

1174 Ch62 LER #79-045

TOLEDO EDISON COMPAW DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-79-50 PAGE 2 -

Failure Data: Three previous incidents of Channel 2 BWST level bistables being out of tolerance were rr 'rted in Licensee Event Reports NP-33-78-84, NP-33-78-133, and hT-33-79-06.

LER #79-045 e

9 1174 063-