ML19210E552
| ML19210E552 | |
| Person / Time | |
|---|---|
| Site: | 05000363 |
| 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 7912050235 | |
| Download: ML19210E552 (1) | |
Text
UNITED STATES o,,
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NUCLEAR REGULATORY COMMISSION g
s REG!ON I
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631 PARK AVENUF KING OF PRUSSIA, PENNSYLVANIA 19406 Docket No. 50-363 NOV 2 01373 Jersey Central Power & Light Company ATTN:
Mr. I.
P..
Finfrock, Jr.
Vice President 260 Cherry Hill Road Parsippany, New Jersey 07054 Gentlemen:
The enclosed IE Bulletin 79-26 is forwarded to you for information. No written response is required. If you desire aaditional information regarding this matter, please contact this office.
Sincerely, 3:2:P7/SN,
cyce H. Grier irector
Enclosures:
1.
List of Recently Issued IE Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encls:
M. K. Pastor, Project Manager 1500 128 26 O
voisose
ENCLOSURE 1 UNITED STATES SSINS:
6820 NUCLEAR REGULATORY COMMISSION Accession No.:
OFFICE OF INSPECTION AND ENFORCEMENT 7910250475 WASHINGTON, D.C.
205b5 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 gnfined 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 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 concentrHtions grow.
Once primary coolant penetrates g
tne cladding (i.e., tae cracking has progressed through the cladding wall and the helium-lithium pressures are sufficient to open the crack), b ron is J
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).
Itwasfurtheryoundwithsimilarcrackingbutwith'essthan50percentlocal depletion of B
, that leaching did not occur even though primary coolant had penetrated the cladding.
The crat ong 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 redund by 10 percent, which corresponds tc 42 percent B
depletionaveragedoverthetopquarterotthecontrolylade.
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 value to 34 percent.
The safety significance of boron loss is its impact on shutdown capability and scram reactivity.
Although shutdown ca bili is demonstrated shutdown margin tests after refueling, the calcu tests are based on the assumpt;on 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 previously entered into system under:
ANO 1500 129 Nr.
of pages:
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