ML19329B621
| ML19329B621 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 06/14/1977 |
| From: | Batch S, Lingenfelter J TOLEDO EDISON CO. |
| To: | |
| Shared Package | |
| ML19329B545 | List: |
| References | |
| NUDOCS 8002050738 | |
| Download: ML19329B621 (3) | |
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2 CAUSF DESCRIP11oM l Personnel error caused the SFAS actuation.
Loss of Y2 has been deter-I gjl'minedtobeadesignproblemwhichisbeinginvestigatedbythe' vendor.
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- TOLEDO EDISON COMPMW A
DAVIS-BESSE UNIT ONE NUCLEAR POWER STATION SUPPLEw. ENTAL I'* FORMATION FOR LER NP-33-77-6 DATE OF EVENT: May 14, 1977 FACILITY:
Davis-Besse Unit 1 IDENTIFICATION OF OCCURRENCE:
At 0452 hours0.00523 days <br />0.126 hours <br />7.473545e-4 weeks <br />1.71986e-4 months <br /> on May 14, 1977, Safety Features Actuation System (SFAS) Channel 2 and Reactor Protection System (RPS) Channel 2 tripped because of blown fuses.
At 0504 hours0.00583 days <br />0.14 hours <br />8.333333e-4 weeks <br />1.91772e-4 months <br /> while trying to replace the fuses, SFAS Channel 1 and RPS Channel 1 were accidentally tripped causing an SFAS actua-tion-i l
Conditions Prior to Occurrence:
The plant was in Mode 5.
Description of Occurrence:
An Instrument and Contr61 (I&C) Mechanic shorted out a fuse in the Auxiliary Shutdown (ASD) Panel while re=oving a bracket. This caused Inverter YV2 to trip and subsequer.t loss of Y2 Bus.
The fuse on Y2 Bus that feeds the ASD Panel did not blow; the 6 amp fuse in the ASD Panel did blow.
The 225 amp fuse at Inverter YV2 also blew, RPS Channel 2 and SFAS Channel 2 then tripped.
(,jDuring the effort to de-energize SFAS Channel 2 and RPS Channel 2, so that the blown fuses.could be replaced, SIAS Channel 1 was accidentally tripped, thus s'atisfying a two out of four logic which actuated incident levels 1.through 5.
At this time, Source Range Nuclear Instrument (NI) I was out for servicing.
Be-cause of the loss of Y2, NI 2 was also lost' in violation of Technical Specifica-tion (TS) 3.9.2.
SFAS actuated properly isolating the Decay Hear System from the Reactor Coolant System, stopping RCS recirculation in violation of Technical Speci-fication 3.4.1.
Designation of Aeoarent Cause:
While removing a bracket from SFAS Channel 2, an I&C Mechanic dropped it causing a short which tripped the channel.
In order to-replace the blown fuses and restore SFAS Channel 2 to service, an operator was instructed to de-energize SFAS Channel 2 and RPS Channel 2; but he inadvertently removed power from SFAS Channel 1 which cau* sed the SFAS to actuate.
Bus Y2 trip has been determined to be due to a design problem by the inverter vendor, Cyberex.
Analysis of Occurrence:
Since the SFAS actuated correctly and three out of the four essential power supplies were operable, the event did not result in a threat to the health and safety of the public or to stati,on personnel.
Cyberex is currently investigating the problem in YV2 to make design changes to prevent 1
recurrence.
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TOLEDO EDISON COMPANY DAVIS-BESSE UNIT ONE NUCLEAR PO*.T.R STATION SUPPLEMEhTAL INFORMATION FOR LER NP-33-77-6 PAGE 2 l
Corrective Action:
Operator blocked the SFAS actuated components, and returned plant to normal status.
Operator placed Y2 on alternate source and returned Decay Heat Pump to recirculation of the RCS.
i Failure Data: No previous similar events have occurred.
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