ML19256B418
| ML19256B418 | |
| Person / Time | |
|---|---|
| Site: | Humboldt Bay |
| Issue date: | 05/31/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Crane P PACIFIC GAS & ELECTRIC CO. |
| References | |
| NUDOCS 7906180373 | |
| Download: ML19256B418 (1) | |
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e,,,e W At f.U I Citi f. K, C AL If OHNI A 0%9G May 31,1979 Docket fio. 50-133 Pacific Gas and Electric Conpany 77 Beale Street San Francisco, California 94106 Attntion:
Mr. Philip A. Crane, Jr.
Assistant General Counsel Gentlemen:
The enclosed Bulletin fio. 79-12 is forwarded to you for action.
A written response is required.
If you desire additional information regarding this ratter, please contact this office.
Sincerely,
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I p / $'EC h li. En,gelken(f /,
irector
Enclosure:
IE Bulletin flo. 79-12 with Enclosures cc w/ enclosures:
W. Barr, PG&E W. A. Raymond, PG&E y.
E. Weeks, PG&E, Humboldt Bay 7906180 N 3
UtilTED STATES f;UCLEAR REGULATORY COMMISSION OFFICE OF IfiSPECTIO!! AND ENFORCEMEfiT WASHIf!GTON, D.C.
20555 flay 31, 1979 IE Bulletin fio. 79-12 SHORT PERIOD SCRAMS AT BWP, FACILITIES Sunmary:
Reactor scrans, resulting from periods of less than 5 seconds, have occurred recently at three BWR facilities.
In each case the scran was caused by high flux detected by the IRM neutron nonitors 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 recurrences 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 system high IRM flux scran.
Cescription 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Oyster Creek - On December 14, 1978, the reactor experienced a scram as control rods were being withdrawn for approach to critical, following a scram from full power which had occurred about 15 hours1.736111e-4 days 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 330 degrees F and the reactor pressure was 190 psig.
Because of the high xenon concentration the operators had not made an accurate estirate 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 naintain 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 SPfi 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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