ML19241B676
| ML19241B676 | |
| Person / Time | |
|---|---|
| Site: | Catawba, Perkins, Cherokee  |
| Issue date: | 05/31/1979 |
| From: | James O'Reilly NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| To: | Dail L DUKE POWER CO. |
| References | |
| NUDOCS 7907200170 | |
| Download: ML19241B676 (2) | |
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UNITED ST ATES
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3 f 1979 In Reply Refer To:
RII:JPO 50-413, 50-414 50-488, 50-489 50-490, 50-491 50-492, 50-493 Duke Power Conpany Atta:
L. C. Dail, Vice President Design Engineering P. O. Box 33139 Charlotte, North Carolina 28242 Gentlemen:
No written The enclosed Bulletin 79-12 is forwarded to you for information.
response is required. If you desire additional information regarding this matter, please contact this office.
Sincerely, W
James P. O'Reilly k irector D
Enclosure:
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1 3 7 G79 Duke Power Company cc w/enel:
D. G. Beam, Project Manager Post Office Box 223 Clover, South Carolina 29710 J. T. Moore, Project Manager Post Office Box 422 Gaffney, South Carolina 29340 4
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UNITED STATES NUCLEAR REGULATORY COMMISSION g
OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 May 31, 1979 IE Bulletin No. 79-12 SHORT PERIOD SCRAMS AT BWR FACILITIES Sununa ry:
Reactor scrams, 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 most 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 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Oyster Creek - On December 14, 1978, the reactor experienced a scram as control rods were being withdrawn for approach to critical, following a scram from full power which had occurred about 15 hours1.736111e-4 days 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 renon concentration the operators had not nade an accurate estimate of the critical rod pattern. The operator at the controls was using the SRM count rate, which had changed only slightly, (425 to 450 cps) to guide the approa-h. Control rod 10-43 (first rod in Group 9) was being withdrawn in 'Sotch 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 vben the scram occurred. Failure of the "emargency rod in" switch to maintain contact, due to a bent switch stop, apparently contribuud to the problem.
2.
Browns Ferry Unit 1 - On January 18, 1979, the reactor experienced a scram during the initial cpproach 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 SRM count rate had led him to believe that the reactor was very suberitical. A short reactor period, estisu.ed at 5 secondt, was experienced. The operator was attempting to reinsert control rods when the scram occurred.
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