ML19209D277

Supplemental Info to LER 78-114/03L-2:on 781110,borated Water Storage Tank Low Level Trip Setpoint Out of Tolerance. Caused by Noisy Constant Current Test Potentiometer within Safety Features Actuation Sys Cabinet

ML19209D277
Person / Time
Site:	Davis Besse
Issue date:	12/07/1978
From:	Kovach S TOLEDO EDISON CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
Shared Package
ML19209D272	List: ML19209D271 ML19209D277
References
LER-78-114-03L, LER-78-114-3L, NUDOCS 7910220299
Download: ML19209D277 (3)

Text

U. S. NUCLEAR REGULATORY COMMISSloN NRC FORM 366 *

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- LICENSEE EVENT REPORT (PLEASE PRINT OR TYPE ALL REQUIRED INFORMATION)

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0 l 7D ATE 7 8 EQ 61 DOCKET NuveER EVENT DESCRIPTION AND PROB ABLE CONSEQUENCES h o 2 l At 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> on 11/10/78 during the performance of surveillance testing, it was dis- 1 o a I covered that the Borated Water Storage Tank (BWST) low level trip setpoint was out ofl o 4 l tolerance (at 59.25 inches H 0) 2 on Saf ety Features Actuation System (SFAS) Channel 2. I o s i Technical Specification 3.3.2.1 states that BWST level instrument strings shall be i l o is l [ operable in Modes 1, 2, and 3 with trip setpoint 249.5 and $55.0 inches H,0. The I o 7 l other three BWST low level instrument strings were operable during the period that l I the setpoint for Channel 2 was out of tolerance. (NP-33-78-133) 1 Lo 8 80 DE CODE SU8CO E COYPONENT CODE SUBC DE SU DE 1 o_1]8 l llBl@ b @ lEl@ lI 9 10 11 12 IJ N l S l T l R l U lh J @ (Z_J 18 19 20 REVISION SEQUENTI AL OCCURRENCE REPORT REPORT NO. CODE TYPE NO.

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44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS h i o l On May 2, 1979 during Mode 5 operation, investigation under IC-246_-79 began. A noisyi i i  ! constant current test potettiometer located within the SFAS cabinet was found to be 1 2

, 2 l the cause of the drifting setpoint. THe potentiometer was replaced, and the bistable 1 i 3 l successfully retested by the performance of Surveillance Test ST 5031.01 and ]

f7T41 I declared operable on May 4, 1979.

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TOLEDO EDISON COMPANY DAVIS-BESSE NUCLEAR POWER STATION UNIT ONE SUPPLEMENTAL INFORMATION FOR LER NP-33-78-133 s

DATE OF EVET: November 10, 1973 FACILITY: Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE: Borated Water Storage Tank (BWST) low level trip sutpoint in Safety Features Actuation System (SFAS) Channel 2 was out of tolerance Conditions Prior to Occurrence: The unit was in Mode 1, with Power (!Bir) = 1356, and Load (MWE) = 450.

Description of Occurrence: At 1130 hours0.0131 days <br />0.314 hours <br />0.00187 weeks <br />4.29965e-4 months <br /> on November 10, 1978 during the perfor-mance of Surveillance Test ST 5031.01, "SFAS Monthly Test" on SFAS Channel 2, it was noticed that the BWST low level trip setpoint was out of tolerance (at 59.25 inches H2 0).

This occurrence placed the unit in Action Statement 9 of Technical Specification 3.3.2.1. This technical specification states that BWST level instrument strings shall be operable in Modes 1, 2, and 3 with trip setpoint 2: 49.5 and ;6 55.0 inches H2 0. Action Statement 9 states that with one channel inoperable, operation may proceed provided (a) the inoperable unit is placed in the tripped condition within ,

an hour, and (b) three other channels are operable.

Designation of Apparent Cause of Occurrence: The cause of this occurrence was 2 initially attributed to instrument drif t of the bistable. However, on May 2, 1979, under Maintenance Work Order IC 246-79, investigation showed the cause to be a noisy constant current test potentiometer located within the SFAS cabinet.

Analysis of Occurrence: There was no danger to the health and safety of the public or to unit personnel. The other three EWST low level instrument strings were opera-ble during the period that the setpoint for Channel 2 was out of tolerance. If a Loss of Coolant Accident had occurred, the suction of the Decay Heat Pumps and Containment Spray Pumps would have been transferred to the Emergency Sump at the proper BWST level since at least two channels are required to trip for an initia-tion of incident level 5.

Corrective Action: On May 2, 1979, during Mode 5 operation, investigation under IC-246-79 began. A noisy constant current test potentiometer located within the 2 SFAS cabinet was found to be the cause of the drif ting setpoint. The potentio-meter was replaced, and the bistable successfully retested by the performance of Surveillance Test ST 5031.01 and declared operable May 4, 1979.

LER #78-114 1173 101

TOLEDO EDISON COMPA'iY DAVIS-BESSE NUCLEAR POWER STATION U'iIT ONE PAGE 2 SUPPLDIENTAL INFORMATION FOR LER NP-33-78-133 s Failure Data: There has been no previously reported occurrence of an out of tol-erance BWST level trip setpoint due to instrument drift. In Licensee Event Report NP-33-78-84, a BWST level indication channel was reported to have been out of tol-erance due to component failure of the level trip module.

LER #78-114 o

O

'1173 102