ML19339A513
| ML19339A513 | |
| Person / Time | |
|---|---|
| Site: | Zimmer |
| Issue date: | 10/31/1980 |
| From: | Flynn J CINCINNATI GAS & ELECTRIC CO. |
| To: | Schwencer A Office of Nuclear Reactor Regulation |
| References | |
| IEB-80-07, IEB-80-7, NUDOCS 8011040168 | |
| Download: ML19339A513 (2) | |
Text
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,[ eh M, TIIE CINCINNATI GAS & ELECTitIC CONII*ANY CINCINN ATI.OHBO 452O5 Docket 7;o. 50-358 October 31, 1980 Mr. A. Schwencer, Chief Licensing Branch No. 2 Division of Licensing U.S.
Nuclear Regulatory Commission Washington, D.C.
20555 RE:
WM. H.
ZIMMER NUCLEAR POWER STATION -
UNIT 1 - BWR JET PUMP HOLDDOWN BEAMS
Dear Mr. Schwencer:
In your letter of June 6, 1980 to Mr. E. A.
- Borgmann, you requested that CG&E respond with respect to the item identified by I&E Bulletin 80-07 concerning observations at the Dresden Nuclear Power Plant.
The attachment to this letter constitutes our response to your request for information.
Very truly yours, THE CINCINNATI GAS & ELECTRIC COMPANY By J
S D. FLYNN, Manager Licensing and Environmental Affairs JDF: dew Enclosure cc:
Charles Bechhoefer Glenn O. Bright Frank F.
Hooper Troy B. Conner, Jr.
James P..Fenstermaker Steven G. Smith William J. Moran J.
Robert Newlin William G. Porter, Jr.
Earl A.
Borgmann F. T.
Daniels W.
Peter Heile Leah S. Kos.k John D.
WGLiver Mary Reder David K. Martin Robert A. Jones Andrew B. Dennison 8011040/6Y g
' RESPONSE NRC POSITION' ON BhR JET Pus 1P HOLDD0hN BEMtS Response to Question 1 Evaluations performed by General Electric (GE) has detemined that beam failures have resulted from intergranalar stress corrosion cracking. A com-parison of the failed -BhR 3 heum,dth :che BhR 4-6 beam, as used on Zimmer, indicates that the Zimmer beam operates at a peak stress 14% lower than the BhR 3 beam at the present preload. - Since time to' failure is dependent en applied. stress, the BhR 4-6 beams, as presently designed and installed, are predicted to have a longer life.
Response to Question 2 A reduction-of the 30 -kip preload currently specified for BhR 4-6 beams to 25 kip will yield a significant factor of improvement in predicted time to crack initiation. Using relationships developed from field experience and-laboratory stress corrosion tests, minimum time to crack initiation of the Zimmer jet pump beam is estimated to increase by at least a: factor of four with respect to the BhR 3 jet pump beam. Additional testing to be conducted through 1981 should make it possible to more accurately predict the expected life of beams with preload reduction. The operational acceptability of this reduced preload has been demonstrated by tests in the GE high flow test facility.
Based on current test data, the preload reduction is expected to increase the beam operating time to crack initiation, at a 2.5% probability level, to a-range of-19 to 40 years.
Based on information available to date, the preload reduction as described above is expected to be a long-term solution for BhR's 4-6 and w uld be adopted 4
by Zimmer.
i Response to Question 3 If a long-tem solution is not agreed upon, periodic inspections of the' l
Zimmer holddown beams would be conducted as a part of the ISI Program. The inspection frequency will be determined on the basis of results obtained from operating plants of _ the same design with surveillance programs currently in place. Crack propagation rates are slow enough to be readily detected during scheduled outages without fear of undetected cracks developing into breaks between outages. Surveillance via ultrasonic inspection can detect cracks in jet pump beams and would likely be employed on Zimer.
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