ML19253C407
| ML19253C407 | |
| Person / Time | |
|---|---|
| Site: | Bailly |
| Issue date: | 11/20/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Shorb E NORTHERN INDIANA PUBLIC SERVICE CO. |
| References | |
| NUDOCS 7912050388 | |
| Download: ML19253C407 (1) | |
Text
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NUCLEAR REGULATORY COMMISSION g
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799 ROOSEVELT ROAD e
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GLEN E LLYN, ILLINOIS 60137 Docket No. 50-367 "trf o f ' ';'4.
Northern Indiana Public Service Compa y ATTN:
Mr. Eugene M. Shorb Senior Vice President 5265 Hohman Avenue Hammond, IN 46325 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 th's matter, please contact this office.
Sincerely, h
ames G. Keppler Director Enc.' osu re :
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 1502 333
/
7912050
UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.
OFFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
20555 November 20, 1979 IE Bulletin Nc. 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 tr.,ron loss have so far been confined to locations in the poison tubes with more than 50 percent Boron-10 (B10) local depletion.
Observea 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 gr>w.
Once primary coolant penetrates 4
the cladding (i.e., the cracking has progressed througn 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 percent local depletion of B
, that leaching did not occur even though primary coolant had penatrated the cladding.
The cracking and boron loss shorten the m: sign 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 1 depletion averaged over the top quarter of the control blade.
Because of the 10 leaching mechanism, GE has reduced the allowance for B depletion aver d
r the top quarter of the control blade fr The safety significance of boron loss i DUPLICATE DOCUMENT scram reactivity.
Although shutdown cap Entire document previously 1502 434 e"te"d i"'
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