ML19338D589
| ML19338D589 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/29/1980 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| NUDOCS 8009230519 | |
| Download: ML19338D589 (1) | |
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UNITED STATES '
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NUCLEAR REGULATORY COMMISSION g
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REGION I 4
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,o',g KING OF PRUSSIA, PENNSYLVANIA 19406 August 29, 1980 Docket No. 50-245 Northeast Nuclear Energy Company ATTN:
Mr. W. G. Counsil Senior Vice President - Nuclear Engineering and Operations P. O. Box 270 Hartford, Connecticut 06101 Gentlemen:
Enclosed is IE Bulletin No. 79-26, Revision 1, which requires action by you with respect to your nuclear power facility (ies).
The original IE Bulletin No. 79-26 has been revised to adjust the required completion date for reporting the results of examination of an exposed control blade and to correct a typographical error.
The revision is identified by use of "R1" in the right margin.
In order to assist the NRC in evaluating the value/ impact of each Bulletin on licensees, it would be helpful if your would provide an estimate of the manpower expended in conduct of the review and preparation of the report (s) required by the Bulletin.
Please estimate separately the manpower associated with corrective actions following identification of problems through the Bulletin.
Should you have any questions regarding the Bulletin or actions required by you, please contact this office.
Sincerely, reeJ/, $lde P yce H. Grier
- ector
Enclosures:
1.
IE Bulletin No. 79-26, Revision 1 2.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) 8009230519'
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Northeast Nuclear Energy Company 2
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cc w/encls:
E. J. Mroczka, Station Superintendent D. G. Diedrick, Manager of Quality Assurance l
J. R. Himelwright, Licensing Safeguards Engineer I, -
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SSINS No.: 6820 Accession No.:
UNITED STATES 8006190042 NUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 August C, 1930 IE Bulletin No. 79-26 Rev. 1 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 baron poison matarial.
Hot cell examinations of both foreign and domestic blades have revealed cracks nt:ar the upper end of stainless steel tubing and loss of boron from the tubes.
The cracks and boron loss have so far been gnfined to locations in the poison tubes with more than 50 percent Boron-10 (8 ) 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 3
B C as helium and lithium concentrations grow.
Once primary coolant penetrates gthe 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 B local depletion (local depletion is considered to be twice the average depletion).
Itwasfurtherfundwithsimilarcrackingbutwthlessthan50percentlocal i
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 wgth of the blade is reduced by 10 percent, which cnrresponds to 42 percent B depletionaveragedoverthetopquarterofthecontrolglade.
y Because of the leaching mechanism, GE has reduced the allowance for B deple-tion 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 calculated control blade worths used in the tests are based on the assumption that no boron loss has occurred.
Reduction in scram reactivity due to boron loss could increase the severity of Critical Power nt transients and could increase nts.
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