05000206/LER-1981-028, Forwards LER 81-028/01T-0.Detailed Event Analysis Submitted

Forwards LER 81-028/01T-0.Detailed Event Analysis Submitted

ML20033A303
Person / Time
Site:	San Onofre
Issue date:	11/13/1981
From:	Ray H SOUTHERN CALIFORNIA EDISON CO.
To:	Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20033A304	List: 05000206/LER-1981-028, Forwards LER 81-028/01T-0.Detailed Event Analysis Submitted 05000206/LER-1981-028-01, /01T-0:on 811030,during Safety Injection Sys Testing,Safeguards Load Sequencer 2 Failed Due to Internal Lockup Condition in Logic Card.Caused by Design Weakness in Card.Procedure Changes Implemented
References
NUDOCS 8111250141
Download: ML20033A303 (2)

LER-1981-028, Forwards LER 81-028/01T-0.Detailed Event Analysis Submitted

Event date:
Report date:
2061981028R00 - NRC Website

text

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RECEIVED mig Southern California Edison Cdmpany WE S AN ONOPRE NUCLE AR GENER ATING STA TION t

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E Walnut Creek, California 94596-5368 Attention: Mr. R. H. Engelken, Director DOCKET No. 50-206 SAN ON0FRE-UNIT 1

Dear Sir:

This letter provides the follow up report describing a reportable occurrence involving the Safeguard Loads Sequencing System. Submittal is in accordance with Section 6.9.2a of Appendix A to the Provisional Operating License DPR-13. This occurrence was initially reported by our letter of October 30, 1981.

During the shutdown for the safety injection repair it was noted that No. 2 sequencer failed to operate during testing.

It was determined that this was a result of the sequencer logic card being locked up due to an abnormal resetting operation. The abnormal operation consisted of resetting the sequencer in the presence of a safety injection trip signal and absence of a block signal.

If the trip signal subsequently is removed, the sequencer logic card lights will indicate that the sequencer is fully reset.

In fact, in this condition, the logic card will not generate a Safety Injection Actuation Signal upon receipt of a safety injection trip signal. Manual initiation is not affected. The locked up condition can be positively removed by a subsequent resetting operation in the absence of a trip signal.

Procedural changes have been implemented to prevent the above described abnormal resetting operation. Preliminary results of a design review indicate that this situation results from an undesirable feature of the logic cards design. Although procedural changes are adequate to protect against this locked up condition, it is considered prudent to pursue a design improvement to the sequencer hardware which would eliminate the concern altogether. Such a design change is presently under investigation in conjunction with the manufacturer. It is anticipated that this change 8111250141 8111 7 N

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1 will be implemented promptly following an extensive review and. testing program.

If you should require additional information, please contact me.

Sincerely, Enclosure: Licensee Event Report'81- 028-cc:

U.' S. Nuclear Regulatory Commission _

Office of Inspection and Enforcement U. S. Nuclear Regulatory' Commission-Office of Management Information & Program Control (MIPC)

Institute of Nuclear Power Operations L. F. Miller (USNRC San Onofre Unit 1_ Resident Inspector) 6