ML19210E565
| ML19210E565 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Daltroff S PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| References | |
| NUDOCS 7912050277 | |
| Download: ML19210E565 (1) | |
Text
er no ug 7 p-E(g
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((i NUCLEAR REGULATORY COMMISSION REGION I 3 J 't.'
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631 PARK AVENUE
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Docket Nos. 50-277 50-278 NOV 201373 Philadelphia Electric Company ATTN:
Mr. S. L. Daltroff Vice President Electric Production 2301 Market Street Philadelphia, Pennsylvania 19101 Gentlemen:
The enclosed IE Bulletin 79-26 is forwarded to you for action. A written response is required. If you desire additional information regarding this matter, please contact this office.
Sincerely,
$2:WAN,
[da oyce H. Grier rector
Enclosures:
1.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encis:
W. T. Ullrich, Station Superintendent Troy B. Conner, Jr., Esquire Eugene J. Bradley, Esquire Raymond L. Hovis, Esquire Michael J. Scibinico, II, Assistant Attorney General 1500 160 29uop D /
ENCLOSURE 1 UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.:
0FFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
20555 IE Bulletin No. 79-26 Date: November 20, 1979 Page 1 of 4 BORON LOSE 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 b ron 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 losshavesofarbeenggnfinedtolocationsinthepoisontubeswithmorethan 50 percent Boron-10 (B
) 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 g
8 C as helium and lithium concentrdtions grow.
Once primary coolant penetrates 4tne cladding (i.e., the cracking has progressed through the cladding wall and thehelium-lithiumpressuresaresufficienttoopenthecrack),ggronis leached out 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 with similar cracking but with less than 50 percent local 1
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 wggth of the blade is reduced by 10 percent, which corresponds to 42 percent B
depletionaveragedoverthetopquarterofthecontrolglade.
Because of y
the leaching mechanism, GE has reduced the allowance for 8 depletion averaged over the top quarter of the control blade from the 42 percent value to 34 percent.
The safety significance of boron loss is its impact on shutdown capability and scram reactivity.
Although shutdown capability __is d_emonstna margin tests after refueling, the calcu tests are based on the assumption that in scram reactivity due to borcn loss c Power Ratio (CPR) reductions during the DUPLICATE DOCUMENT the consequences of control rod drop ac Entire document previously entered into systen under:
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