ML19225A817
| ML19225A817 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 05/31/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Howell S CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| NUDOCS 7907200307 | |
| Download: ML19225A817 (1) | |
Text
E p" "8 Go UNif f D STxTES g
,g NUCLEAR REGULATORY COMMISSION E
iE REGION 111 o
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CLEN ELLYN. ILLINOl$ 60137 MAY 311979 Docket No. 50-329 Docket No. 50-330 Consumers Power Company ATTN:
Mr. Stephen H. Howell Vice President 1945 West Parnall Road Jackson, MI 49201 Gentlemen:
The enclosed IE Pulletin No. 7;-12 is forwarded to you for in fo rma tion.
No written response is required.
If you desire additional information regarding this inatter, please contact this office.
Sincerely, James G. Kepp er Director
Enclosure:
IE Bulletin No. 79-12 cc w/ encl:
Central Files Director, NRR/DPM Director, hRR/ DOR PDR Local PD3 NSIC TIC Ronald Callen, Michigan Public Service Ccmmission Dr. Wayne E. North Lycon M. Cherry, Chicago 415 338 q so7 200 3G7
U.S. NUCLEAR REGULATORY COFS!ISSION OFFICE OF INSPECTION AND ENFORCEMEST REGION III Ly 31, 1979 IE Eulletin No. 79-12 SHORT PERIOD SCRAMS AT BWR FACILITIES Su==ary'.
Reactor scraes, resulting from periods of less than 5 seconds, have occtirred rece.ntly at turce BWR facilities. In each case the scra= vas causr_d by high flux detected by the IRM neutron mcnitors during an approach to critical.
These events are similar in cost 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 appropr! ate to further reduce the number of challenges to the reactor protective syste= high IRM flux scrac.
Description of Circumstances:
The fellowing is a brief account of each event.
1.
Oyster Creek - On December 14, 1978, the reactor experienced a scra: as control rods were being withcrawn for approach to critical, following a scra= 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 tecperature was 380 dagrees F and tne reactor pressure was 190 psig.
Because 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 S2M count ate, 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 pcsition 10, when the reactor became critical on an esticated 2.8 second period. The operator was attempting to reinsert the rod when the scra=
occurred. Failure of the " emergency rod in" switch to nainhin contact, due to a bent owitch stop, apparently contributed to the pro,le=.
2.
Browns Ferry Unit 1 - On January 18, 1979, the rea cor experienced a scram during the initial approach to critkal fol.'
sing refueling. The operator was continuously withdrawing in " notch override" the first centrol rod in Group 3 (a high worth rod) because the SRM count rate had led him to believe the the reactor was very suberitical. A short reactor pericd, estimated at 5 seconds, was erperienced. The operator was attempting to reinsert control rods when the scra= occurred.
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