ML19296A393
| ML19296A393 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/16/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Johari Moore SOUTHERN CALIFORNIA EDISON CO. |
| References | |
| NUDOCS 7903190517 | |
| Download: ML19296A393 (1) | |
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>t NUCLEAR REGULATORY COM?,11sSION f
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WALNUT CREEK, C AllFOR NI A 94596 February 16, 1979 Docket tios. 50-206 50-361 50-362 Southern California Edison Company P. O. Box 800 2244 Walnut Grove Avenue Rosemead, California 91770 Attention: Mr. Jack B. 11oore Vice President Gentlemen:
This Information Notice is provided as an early notification of a possibly significant matter.
It is expected that recipients will review the information for possible applicability to their facilities.
fio specific action or response is requested at this time.
If further NRC evaluations so indicate, an IE Circular, Bulletin or NRR Generic Letter will be issued to recommend or request specific licensee actions.
If you have questions regarding the matter, please contact the Director of the appropriate llRC Regional Office.
Sincerely, b m cG[2.
R. H. Engelken Director
Enclosures:
l.
IE Information Notice No. 79-04 2.
List of IE Information Notices Issued in 1979 cc w/encls:
J. M. Curran, SCE J. T. Head, SCE J. H. Drake, SCE 79031905/7
UNITED STATES 9
NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND E50RCEMENT WASHINGTON, D.C.
20555 February 16, 1979 IE Information Notice No. 79-04 DEGRADATION OF ENGINEERED SAFETY FEATURES Summary On September 16, 1978, an unusual sequence of events occurred at Arkansas Nuclear One, Units 1 and 2.
The events involved the electrical power sources and culminated in the spurious activation and degraded operation of Unit 2 Engineered Safety Features (ESF). Analysis of the course of the incident has identified three safety concerns in the electrical distribution system operation and design.
(1) The offsite power supply for ANO Unit 1 Engineered Safety Feature loads was deficient in that degraded voltage could have resulted in the unavailab'lity of ESF equipment, if it were to be needed.
(2) The design of the ANO site electrical system that provides offsite power to Units 1 and 2 did not fully meet the Commission's Regula-tions, 10 CFR 50, Appendix A, General Cesign Criterion 17, because in certain circumstances a loss of one of the two offsite power circuits would also result in a loss of the other such circuit.
(3) Deficiencies existed in the operation cf the Unit 2 inverters that convert DC to AC power for the uninterruptable 120 volt vital AC buses.
Desc
' ion of Circumstances Initially Unit I was operating at 100 percent power; Unit 2 was in hot standby performing hot functional testing in preparation for initial criticality and power operation (l) Unit 1 auxiliary electrical loads were being supplied from the Unit 1 main generator via the unit auxiliary transformer. Unit 2 auxiliary electrical loads were being fed from the offsite grid through Startup Transformer No. 3.
The normal operating status was interrupted by the failure of the Unit 1 Loop "A" Main Steam Line Isolation Valve (MSIV) air operator solenoid causing the MSIV to close as designed. The Unit 1 Reactor Protection System sensed conditions requiring reactor shutdown and tr:gped the reactor.
The 1 The Unit 2 Operating License did not permit criticality of power operation at the time of the incident.
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