ML19254A668
| ML19254A668 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/31/1979 |
| From: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Van Brunt R ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR |
| References | |
| NUDOCS 7907200367 | |
| Download: ML19254A668 (1) | |
Text
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NUCLE AR REGULATORY COMMISSION
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HEGION V 0, ',A /s,j)3 1930 f t CAltFORtJI A UOtJLE VARD Q
s SulTE 202 WALfJUT CHE EK PL AZA e,,.e WALfJU T CR E E V, CAllF ORlJI A DU/)G May 31, 1979 Docket flos. 50-528 50-529 50-530 Arizona Public Service Company P. O. Box 21666 Phoenix, Arizona 83036 Attention: f4r. E. E. Van Brunt, Jr.
Vice President, Construction Projects Gentlemen:
The enclosed Bulletin flo. 79-12 is forwarded to you for information.
llo written response is required.
If you desire additional information regard-ing this matter, please contact this office.
Sincerely, i
< l s jfftitc
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I.if.Engelkenc.
firector
Enclosure:
IE Bulletin fio. 79-12 with Enclosures cc w/ enclosures:
F. W. Hartley, APS k.
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1907200S67.1,
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UtlITED STATES f;UCLEAR REGULATORY COMMISS10fl 0FFICE OF If4SPECT10fl AliD Ef;FCRCEMElli WASHlfiGT0tl, D.C.
20555 May 31, 1979 IE Bulletin flo. 79-12 SHORT PERIOD SCRAMS AT BWR FACILITIES Surrary:
Reactor scrans, resulting from periods of less than 5 seconds, have occurred recently at three C',lR 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 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 IRf1 flux scram.
Description of Circumstances:
The following is a brief account of each event.
1.
Oyster Creek - On Decerter 14, 1978, the reactor experienced a scram as control rods were being withdrawn for approach to critical, following a scram from full power which had occurred about 15 hours1.736111e-4 days 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 estir' ate 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 became 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 critical following refueling. The operator was continuously withdrawing in " notch override" the first control rod in Group 3 (a high worth rod) because the SPM 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 cccurred.
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