ML19253C414
| ML19253C414 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 11/20/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Wachter L NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 7912050404 | |
| Download: ML19253C414 (1) | |
Text
th fa ancoq'o UNITED STATES NUCLEAR REGULATORY COMMISSION n
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E REGION 111 o,
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799 ROOSEVELT ROAD
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'NO GLEN ELLYN, ILLINOIS 60137
- ....f Docket No. 50-282 Docket No. 50-306 Northern States Power Company ATTN:
Mr. Leo Wachter Vice President Power Production and System Operation 414 Nicollet Mall Minneapolis, MN 55401 Gentlemen:
The enclosed IE Bulletin No. 79-26 is forwarded to you for information.
No written response is required.
If you desire additional information regarding this matter, please contact this office.
Sincerely,
% Y.
V
,. James G. Keppler Director
Enclosure:
IE Bulletin No. 79-26 cc w/ encl:
Mr. F. P. Tierney, Jr.,
Plant Manager Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC John W. Fer'. nan, Ph.D.,
Nuclear Enginet,, MPCA 1502 337 7012050
UNITED STATES SSINS:
68?0 NUCLEAR REGULATORY COMMISSION Accession No.
OFFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
20555 November 20, 1979 IE Bulletin No. 79-26 BORON LOSS FROM BWR CONTROL BLADES Description of Circumstances:
The General Electric Companj (GE) has informed us of a failure mode for control blades whict can cause a loss of boron poison material.
Hot cell examinations of both foreign and domestic blades have revealed cracks near the upper end of stainless steel tubing and loss of boron from the tubes.
The cracks and boron loss have so far been confined to locations in the poison tubes with more than 50 percent Boron-10 (B10) local depletion.
Observed crack sizes range from a quarter to a half inch in length and from one to two mils in width.
GE has postulated that the cracking is due to stress corrosion induced by solidification of boron carbide (B C) particles and swelling of the compacted 4
B C as helium and lithium concentrations grow.
Once primary coolant penetrates 4
the claddi-(i.e., the cracking has progressed through the cladding wall and the helium-litn.um pressurcs are sufficient to open the crack), baron is leached out 10 of the tube at locations with more than 50 percent B local depletion (local depletiel is considered to be twice the average depletion).
It was further found 10 with similar cracking but with less than 50 percent local depletion of B
, that leaching did not occur even though primary coolant had penetrated the cladding.
The cracking and boron loss shorten the design life of the control blade.
According to the GE criteria the end of design life is reached when the reactivity 10 worth of the blade is reduced by 10 percent, which corresponds to 42 percent B depletion averaged over the top quarter of the control blade.
Because of the 10 or leaching mechanism, GE has reduced the the top quarter of the control blade f DUPLICATE DOCUMENT The safety significance of boron loss Entire document previously scram reactivity.
Although shutdown c entered f.nto system under:
7 k0 dfh ANO 1502
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No. of pages:
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