ML19347E088
| ML19347E088 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/06/1981 |
| From: | Lipinski W ARGONNE NATIONAL LABORATORY |
| To: | Bender M Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1315, NUDOCS 8104150417 | |
| Download: ML19347E088 (2) | |
Text
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ARCONNE NATIONAL LABORATORY Tdtpkre 312/972 7880
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w ei /3/3 February 6, 1981 53330-WCL-020
W E l V E D Mr. M. Bender ADVIS191 C0!.W:TTEE CN E SAIEGUADS. U.S.N.R.C.
Advisory Com=ittee on Reactor Safeguards U. S. Nuclear Regulatory Coc=ission FEB 111W1 Washington, D. C.
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Dear Mr. Bender:
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San Onofre Unit 1, Licensee Event Report for
Subject:
September 2, 1980 The above subject LER reported failure of the Safety Injection Syste:
(SIS) sequencer to lead the diesels on Loss of Of f-Site Power (LOP) if the safety injection block switch is placed in the block position or SIS parameters return to normal. The letter from J. G. Haynes, California Edison Company, to R. H. Engleken, NRC, dated Septe=ber these 16, 1980, stated that the design would be modified to correct deficiencies but did not discuss the proposed changes.
It is to be noted that these design deficiencies represent a ce==on mode f ailure, because both trains of the SIS are affected si=ultaneously.
The first condition which requires correction involves the sequence encountered during nor=al shutdcun.
During a normal shutdown, to actuation of the safety injection system when the pressurizer prevent pressure reaches 1,685 psig, an alarm to alert the operator to block actuation of safety injection is initiated when pressuri:er pressure The operator manually blocks actuation of safety reaches 1,750 psig.
injection by placing the two safety injection block switches in the This action will prevent the automatic (but not manual) block postion.
actuation of the safety injection system and extinguish the alert In the event an LOP occurs following engaging of to block alar =.
the block, the safety injection system loads will trip and the diesels However, the sequencers will not place the diesels will continue to run.
on the 4 kv busses and begin automatic loading of the safety injection system since the saf ety injection actuation signal has been blocked.
The operator will have to either manually load the safety injection equipment or manually initiate automatic actuation at the sequencer The concern with this situation is that the flow of borated panels.
water to the reacor coolant system may be interrupted longer than necessary.due to the safety injection system not being immediately loade.d onto the diesel generators following an LOP.
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February 6, 1981 Mr. M. Sender the remedy for the above deficiency involves removal I assume that If the pressurizer of the block conditions if an LOP occurs.
pressure is 1,685 psig or less, safety injection will occur automatically, and will have to be ter=inated manually.
The second condition which requires correction involves another sequence When pressurizer pressure drops below 1,685 psig, or containment of events.
pressure goes above 2 psig, the sequencers will automatically start the diesel generators and actuate the safety injection system as designed.
Following successful operation of the safety injection system, it is postulated that pressurizer pressure and containment pressure return to Subsequent to return of the SIS actuation parameters their normal range.
to normal, if an LOP occurs the safety injection system loads will trip, However, the sequencers will not and the diesels will continue to run.
place the diesels on the 4 kv busses and begin automatic loading of the safety injection system since the SIS parameters are in the nor=al Actuation of the safety injection system will depend upon operator range.
manual action or reaching of an SIS setpoint.
Since the above sequence of events could occur for a small break LOCA or secendary line break, it would be desirable for the safety injection loads to automatically resequence.
clear as to what the proposed fix is for the second condition.
It is not entitled " Addition of Standby Power and ECCS Modifications The document for Onofre Nuclear (Preliminary Engineering and Safety Analysis Report)
Generating Station, Unit 1, February 1975" states on page 1-24, that "SIAS is continuous until reset by the operator". Has the system been designed without meeting the seal-in feature promised in the PSAR?
The above conditions may not be unique to San Onofre and may exist generically in other plants. It is recommended that existing plants be reviewed to see if they suffer from the same design deficiencies.
i Also a regulatory guide may be required, to provide better guidance j
in the design of ECCS systems.
Sincerely,
/, : i:.
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o s. : /G, Walter C. Lipinski, Ph.D.
Senior Electrical Engineer Reactor Analysis and Safety Division WCL: sir Dist: S. Duraiswamy, ACRS
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