ML19256F692
| ML19256F692 | |
| Person / Time | |
|---|---|
| Site: | Zimmer |
| Issue date: | 12/04/1979 |
| From: | Denise R Office of Nuclear Reactor Regulation |
| To: | Varga S Office of Nuclear Reactor Regulation |
| References | |
| IEB-79-26, NUDOCS 7912200121 | |
| Download: ML19256F692 (2) | |
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UNITED STATES
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WASHINGTON O. C. 20555 nFC 41979 S.,...../
MEMORANCUM FOR: Steven A. Varga, Acting Assistant Director for Light Water Reactors, DPM FROM:
Ric d P. Denise, Acting Assistant Director for Reause Safety, DSS
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION FOR ZIMMER 1 Plant Name:
Zimer 1 Cocket No.:
50-358 Milestone No.:
12-27 Licensing Stage:
CL Responsible Branch:
LWR #1 and Project Manager:
I. Peltier Svstems Safety Branch Involved:
Core Performance Branch Description of Review:
Request for Additional Info mation Review Status:
Comolete The Reactor Fuels Section of the Core Performance Branch has crecared the enclosed recuest for additional infomation for the Zimer 1 9
application.
h' M
Richard D. Denise, Acting Assistant Director for Reactor Safety Division of Systems Safety
Enclosure:
As stated cc:
R. Mattson/F. Schroeder D. Vassallo K. Kniel R. Meyer D. Houston J. Stol::
I. Peltier
Contact:
D. Houston, x27603 1851 088
/Al 7912200 4
O
Request For Zimmer i Reactor. Fuels Section 231.12 A copy of IE Bulletin No. 79-26 concerning a recentl3 analyzed failure mode for SWR control rod blades is attached. As a result of observed cracks 'in the control rod cladding, some B C 4
is leached out of the tubes which results in decreased reactivitv worth. The bulletin lists actions to be taken by licensees of all operating BWR plants.
To proceed toward an operating license for your plant, we need to have your comitment to perform the same actions as reouired in the Bulletin.
1851 089
L'NITED STATES
- .t.2 00 0 NUCLEAR REGULATORY COMMISSION Accession No.:
OFFICE OF INSPECTICN AND ENFOP.CE".ENT 7910250t75 WASHINGTON, D.C.
20555 Novemoer 20, 1979 IE Eulletin No. 79-26 BCRCN LOSS FROM EWR C0t. TROL BLADES Description of Circumstances:
The General Electric Company (GE) has informed us of a failure mode for control blades wnich can cause a loss of boren poison =aterial.
Hot cell examinations of both foreign and ccmestic blades have revealed cracks near the upper end of stainless steel tubing and loss of boron from the tubes.
The cracks and baron loss have so far been confined to locations in the poison tubes with more than 50 percent Soron-10 (310) local depletion. Cbserved 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 boren carbide (8 C) particles and swelling of the compacted 4
8 C as helium and lithium concentrations grow. Once primary coolant penetrates 4
the cladding (i.e., the cracking has progressed through the cladding wall and the helium-lithium pressures are sufficient to open the crack), boren is leached out 10 of the tube at locations with more than 50 percent B local depletion (local cepletion is considered to be twice the average depletion).
It was further found IO with similar cracking but witt, less than 50 percent local depletion of B
, that leaching did not occur even though primary coolant had penetrated the cladding.
The cr ' king 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 IO worth of the blade is reduced by 10 percent, which corresponds to 42 percent B depletion averaged over the top quarter of the control blade.
Because of the 10 leaching mechanism, GE has reduced the allowance for 8 depletion averaged over the top quarter of the control blade from the 42 parcent value ree The safety significance of boron i DUPLICATE DOCUMENT scram reactivity. Al though.shutd Entire document previously entered into system under:
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