ML19210E547
| ML19210E547 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W CONNECTICUT YANKEE ATOMIC POWER CO. |
| References | |
| NUDOCS 7912050226 | |
| Download: ML19210E547 (1) | |
Text
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o UNITED STATES E)).3,(f(gg NUCLEAR REGULATORY COMMISSION lT,
- /.E REGION 1 o
631 PARK AVENU2
%,' '.O.. f KING OF PRUSSIA, PENNSYLVANIA 19406
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Docket No. 50-213 f;Tl 2 0 IN9 Connecticut Yankee Atomic Power 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,
%Yo w
h oyce H. Grier irector
Enclosures:
1.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encis:
R. Graves, Plant Superintendent D. G. Diedrick, Manager of Quality Assurance J. R. Himmelwright, Licensing Safeguards Engineer 1500 l1i 226 7 912 0 5(j r
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 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 eacks near the upper end of stainless steel tubir.g and loss of boron from the tubes.
The cracks and boron loss have so far been gnfined to locations in tSe poison :ubes with more than 50 percent Boron-10 (B ) local depletion.
Observed crack sizes range from a quarter to a half inch in length and from cna to two mils in width.
GE has postulated that the cracking is due to stress corrosion induced by solidification of boron carbide (8 C) particles and swelling of the compacted 3
B 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),gronis leached out of the tube at locations with more than 50 percent C local depletion (local depletion is considered to be twice the average depletion).
It was further f und 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 w gth 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 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 capt.H lity 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 DUPLICATE DOCUMENT Power Ratio (CPR) reductions during the the consequences of control rod drop ac Entire document previous 1v entered into system under E /o M o V 7.C.
nuO 1500 112
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