ML19253C417
| ML19253C417 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/20/1979 |
| From: | James Keppler NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | Crouse R TOLEDO EDISON CO. |
| References | |
| NUDOCS 7912050410 | |
| Download: ML19253C417 (1) | |
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UNITED ST ATES
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-t NUCLEAR REGULATORY COMMISSION k,i' 3
REGION lil
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- f GL E N E L LY N. lL LINOIS 6013 7
- y-hl~ S0 bh Docket No. 50-346 Toledo Ediron Company ATTN
Mr. Richard P. Crouse Vice President Energy Supply Edison Plaza 300 Madison Avenue Toledo, OH 43652 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, h b).
e p James G. Keppler U Director
Enclosure:
IE Bulletin No. 79-26 cc w/ encl:
Mr. T. Murray, Statica Superintendent Central Files Director, NRR/DPM Director. NRR/ DOR PDR Local PDR NSIC TIC Harold W. Kohn, Power Siting Commission 1502 343 Helen W. Evans, State of Ohio 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 poi nn 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 (loca',
depletion is considered to be twice the average depletion).
It was further found 10 with similar crecking 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 leaching machanism, GE has reduced the the top quarter of the control blade fr DUPLICATE DOCUMENT The safety significance of boron loss i scram reactivity.
Although shutdown ca Entire document previously entered into system under:
77/OB#0TM 1502 344
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