ML19253C363
| ML19253C363 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Finfrock I JERSEY CENTRAL POWER & LIGHT CO. |
| References | |
| NUDOCS 7912050237 | |
| Download: ML19253C363 (1) | |
Text
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UNITED STATES NUCLEAR REGULATORY COMMISSION y }'
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.n E REGION I 0,
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631 PARK AVENUE
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,e KING OF PRUSSIA, PENNSYLVANIA 19406 9
Docket No. 50-219 NDV 2 0 Ing Jersey Central Power and Light Company ATTN:
Mr. Ivan R. Finfrock, Jr.
Vice President Madison Avenue at Punch Bowl Road Morristown, New Jersey 07960 Gentlemen:
The enclosed IE Bul'etin 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, wkVI. OHan oyce H. Grier ector
Enclosures:
1.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encis:
J. T. Carroll, Station Superintendent 1503 020 7 9120 5 p 2.3 7
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 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 gnfinad to locations in the poison tubes with more than 50 percent Baron-10 (B ) local depletion.
Observed crack sizes range from a quarter to a half inch in length and frcm ene to two mils in width.
GE hi postulated that the cracking is due to stress corrosion induced by solid.fication of boron carbide (B C) particles and swelling of the compacted 4
B C as helium and lithium concentrdtions grow.
Once primary coolant penetrates thecladding(i.e.,thecrackinghasprogressedthroughthecladdingwalland 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).
Itwasfurtherfoundwithsimilarcrackingbutwithlessthan50percentlocal y
depletion of B
, that leaching did not occur even though primuy cco!wt 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 reaccivity w gth of the blade is reduced by 10 percent, which corresponds to 42 percent B
depletionaveragedoverthetopquarterofthecontr31 glade.
Because of the leaching mechanism, GE has reduced the allowance for B depletion averaged over the top quarter of the control blade from the 42 percent salue to 34 percent.
The safety significance of boron loss is its irspact on shutdown capability and scram reactivity.
Although shutdown ca abilit is demonstrated b 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) reduct,1ons during the the consequences of control rod drop ac Entire document prev.tously entered into system imder:
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