ML19256B421
| ML19256B421 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 05/31/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| References | |
| NUDOCS 7906180375 | |
| Download: ML19256B421 (1) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION
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SUIT E' 2"l2, WA Lf;U T CH E E K PL AZA e,,,o WAlfaUT Cilf f K, CAllF ORNI A 9W)G May 31, 1979 Docket tio. 50-312 Sacramento Municipal Utility District P. O. Box 15830 Sacramento, California 95813 Attention:
Mr. John J. Mattimoe Assistant General Manager Gentlemen:
The enclosed Bulletin tio. 79-12 is forwarded to you for information.
No written response is required.
If you desire additional information regard-ing this matter, please contact this office.
Sincerely,
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,M,.H.Engelken7 UDirector
Enclosure:
IE Bulletin flo. 79-12 with Enclosures cc w/ enclosures:
R. J. Rodriguez, SMUD L. G. Schwieger, SMUD 790618 0 3 76~
UtilTED STATES fiUCLEAR REGULATORY COMMISS10ft 0FFICE OF IflSPECTIO!l Af1D Ef;FORCEf4EtlT WASHIfiGT0!1, D.C.
20555 flay 31, 1979 IE Bulletin fio. 79-12 SHORT PERIOD SCRAMS AT BWR FACILITIES Sunnary:
Reactor scrans, resulting from periods of less than 5 seconds, have occurred recently at three BWR facilities.
In each case the scram was caused by high flux detected by the IRM neutron monitors during an approach to critical.
These events are similar in nost respects to events which were previously described by IE Circular 77-07 (copy enclosed).
The recent recurrence, of this event indicate an apparent loss of effectiveness of the earlier Circular.
Issuance of this Bulletin is considered appropriate to further reduce the number of challenges to the reactor protective systea high IRM flux scram.
Description of Circumstances:
The following is a brief account of each event.
1.
Oyster Creek - On December 14, 1978, the reactor experienced a scram as control rods were being withdrawn for approach to critical, following a scram from full power which had occurred about 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> earlier. The moderator temperature was 380 degrees F and the reactor pressure was 190 psig.
Because of the high xenon concentration the operators had not made an accurate estinate of the critical rod pattern.
The operator at the controls was using the SRf1 count rate, which had changed only slightly, (425 to 450 cps) to guide the approach.
Control rod 10-43 (first rod in Group 9) was being withdrawn in " notch override" to notch position 10, when the reactor becane critical on an estimated 2.8 second period.
The operator was attempting to reinsert the rod when the scram occurred.
Failure of the " emergency rod in" switch to maintain contact, due to a bent switch stop, apparently contributed to the problem.
2.
Browns Ferry Unit 1 - On January 18, 1979, the reactor experienced a scram during the initial approach to gritical following refueling. The operator was continuously withdrawing in " notch override" the first control rod in Group 3 (a high worth rod) because the SPJ4 count rate had led him to believe that the reactor was very subcritical.
A short reactor period, estimated at 5 seconds, was experienced. The operator was attempting to reinsert control rods when the scram occurred.
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