ML19210E560
| ML19210E560 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 7912050255 | |
| Download: ML19210E560 (1) | |
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UNITED STATES
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E NUCLEAR REGULATORY COMMISSION g
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,cf KING OF PRUSSIA, PENNSYLVANIA 19406 Docket Nos. 50-336 NOV 2 01373 50-423 Northeast Nuclear Energy Company ATTN:
Mr. W. G. Counsil Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Gentlemen:
The enclosed IE Bulletin 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, W N.
k r t
Enclosures:
1.
List of Recently Issued Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encls:
J. F. Opeka, Station Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himmelwright, Licensing Safeguards Engineer K. W. Gray, Construction Quality Assurance Lead H. R. Nims, Director of Nuclear Projects 1500 143 2 <6 6
p 791203 0
ENCLOSURE 1 UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.:
OFFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
20555 IE Bulletin No. 79-26 s
Date: November 20, 1979 Page 1 of 4 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 ' ave 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 4 5e cracking is due to stress corrosion induced by solidification of baron. carbide (B C) particles and swelling of the compacted 3
8 C as helium and iithium concentr3tions 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).
Itwasfurtherfoundwithsimilarcrackingbutwithlessthan50percentlocal y
depletion of B
, that leaching did not occur even though primary coolant had penetrated the cladding.
The cracking and baron loss shorten the design life of the control blade.
According to the GE criteria the end of design life is reached when the reactivity wgth of the blade is reduced by 10 percent, which corresponds to 42 percent B
depletionaveragedoverthetopquarterofthecontrolglade.
Because of l
the leaching mechanism, GE has reduced the allowance for B 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 demonstrated by shutdown margin tests after refueling, the calcu tests are based on the assumption that in scram reactivity due to boron loss c Power Ratio (CPR) reductions during the DUPLICATE DOCUMENT the consequences of control rod drop acc Entire document previously entered into system under:
}500 144 7r
)9/OM ANO No. of pages: