ML19253C406
| ML19253C406 | |
| Person / Time | |
|---|---|
| Site: | Clinton  |
| Issue date: | 11/20/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Gerstner W ILLINOIS POWER CO. |
| References | |
| NUDOCS 7912050384 | |
| Download: ML19253C406 (1) | |
Text
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UNITE D STATES
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NUCLEAR REGULATORY COMMISSION J'
REGION 111 3
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799 ROOSEVELT ROAD e
GLEN E L LYN, lLLINOIS 60137 It0 V % 0 U /3 Docket No. 50-461 Docket No. 50-462 Illinois Power Company ATTN:
Mr. W. C. Gerstrer Executive Vice President 500 South 27th Street Decatur, IL 62525 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, lu (b James G. Keppler Director
Enclosure:
IE Bulletin No. 79-26 cc w/ encl:
Central Files Director, NRR/DPM Director, NRR/ DOR PDR Local PDR NSIC TIC Mr. Dean Hansell, Office of Assistant Attorney General
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7912050
UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.-
0FFICE 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 Company (GE) has informed us of a failure mode for control blades which 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 cladding (i.e., the cracking has progressed through the cladding wall and the helium-lithium pressures are sufficient to open the crack), boron is leached out 10 of the tube at locations with more than 50 percent B local depletion (local depletion is considered to be twice the average depletion).
It was further found 10 with similar cracking but with less than 50 percer.t 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 leaching mechanism, GE has reduced the the top quarter of the control blade f DUPLICATE DOCUMENT The safety significance of boron loss i Entire document previously scram reactivity.
Although shutdown ca entered into system under:
7?/o6CM
'502 432
^"o No. of pages:
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