ML19246C059
| ML19246C059 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 05/31/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 7907200114 | |
| Download: ML19246C059 (1) | |
Text
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NUCLEAR REGULATORY COMi'(SSION 3-
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May 31,1979 Docket Nos. 50-336 50-423 Northeast Nuclear Energy Company ATTN: Mr. W. G. Counsil Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Gentlemen:
The enclosed Bulletin 79-12 is fuwarded to you for information.
No written response is required.
If you desire additional information reoarding this matter, please contact this office.
Sincerely, 7
Boyce H. Grier
' Director
Enclosures:
1.
List of IE Bulletins Issued in Last Twelve Months cc w/encls:
K. W. Gray, Construction Quality Assurance Lead H. R. Nims, Director of Nuclear Projects J. F. Opeka, Station Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himelwright, Licensing Saftiguards Engineer 7 9 07 2 0'J 1 ( '(
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UNITED STATES NUCLEAR REGULATORY COMMISSION OFF. 'E OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Bulletin No. 79-12 Date: May 31, 1979 Page 1 of 3 SHORT PERIOD SCRAMS AT BWR FACILITIES Summary:
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 indic te 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Oyster Creek - On December 14, 1978, the reactor experiencej a scram as control rods were being withdrawn for approach to critical, following a scram from full power which haa occurred about 15 hours1.736111e-4 days 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.
Jecause of the high xenon concentration the operators had not made 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 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 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 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 subcritical.
A short reactor period, estimated at 5 seconds, was experienced.
The operator was attempting to reinsert control rods when the scram occurred.
DUPLICATE DOCUMENT l.a,s Ub, b Entire document previously entered into system under:
ANO 11 No. of pages:
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