ML19210E556
| ML19210E556 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 11/20/1979 |
| From: | Grier B NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I) |
| To: | Arnold R METROPOLITAN EDISON CO. |
| References | |
| NUDOCS 7912050248 | |
| Download: ML19210E556 (1) | |
Text
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....ps arow gf UNITED STATES y Y)e g
NUCLEAR REGULATORY COMMISSION i
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.: E REGION I o SD f#
631 PARK AVENUE
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- O.....f KING OF PRUSSIA, PENNSYLVANIA 19406 Docket Nos. 50-289 NOV 2 0 m3 50-320 Metropolitan Edison Company ATTN:
Mr. R. C. Arnold, Sr.
Senior Vice President 100 Interpace Parkway 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 additional information regarding this matter, please contact this office.
Sincerely, hk h
oyce H. Grier
'-0Trector
Enclosures:
1.
List of Recently Issued Bulletins CONTACT:
D. L. Caphton (215-337-5266) cc w/encls:
J. G. Herbein, Vice President Nuclear Operations E. G. Wallace, Licensing Manager G. P. Miller, Manager Support Services and Logistics G. P. Miller, Acting, Superintendent Unit 1 W. E. Potts, Unit 1 Superintendent - Technical Support J. J. Colitz, Manager Plant Engineering R. F. Wilson, Director TMI-2 Recovery, Acting J. B. Logan, Superintendent Unit 2 G. A. Kunder, Unit 2 Superintendent - Technical Support I. R. Finfrock, Jr.
R. W. Conrad G. '. Trowbridge, Esquire J. 8. Lieberman, Esquire Ms. Mary V. Southard, Chairperson, Citizens for a Safe Environment John T. Collins, Deputy Director, NRC, TMI Support 1500 136 79120504
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 B0RON 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 ggnfined to locations in the poison tubes 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 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 g
tne cladding (i.e., the cracking has progressed through the cladding wall and thehelium-lithiumpressuresaresufficien;toopenthecrack),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).
It was furtherfound with similar cracking but with less than 50 percent local depletion of 8
, 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 wggth of the blade is reduced by 10 percent, which corresponds to 42 percent B
depletionaveragedoverthetopquarterofthecontro1 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 value to 34 percent.
The safety significance of boron loss is its impact on shutdown capability and scram reactivity.
Although shutdown c
~'
~
margin tests after refueling, the calc tests are based on the assumption that in scram reactivity due to boron loss Power Ratio (CPR) reductions during th DUPLICATE DOCUMENT the consequences of control rod drop a Entire document previously entered into system under:
1500 137
^"o 77/o86W75' No. of pages: