ML18086B730
| ML18086B730 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 09/22/1981 |
| From: | Fay C WISCONSIN ELECTRIC POWER CO. |
| To: | Brooke Clark, Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8109290301 | |
| Download: ML18086B730 (2) | |
Text
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Wlscons1n Electflc POWER coMPANY 231 W. MICHIGAN, P.O. BOX 2046, MILWAUKEE, WI 53201 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. NUCLEAR REGULATORY COMMISSION Washington, D. c.
20555 Attention:
Mr. Robert A. Clark, Chief Operating Reactors Branch 3
- Gentlemen:
September 22, 1981 DOCKET NOS. 50-266 AND 50-301 INSPECTION CRITERIA FOR TURBINE DISC CRACKING POINT BEACH NUCLEAR PLANT, UNITS 1 AND 2 By letter dated August 21, 1981, the NRC requested that Wisconsin Electric Power Company, Licensee for the Point Beach Nuclear Plant Units 1 and 2, provide a commitment to use the four criteria presented in the safety evaluation attached to that letter for future turbine rotor disc inspections.
These inspection criteria were developed in conjunction with the Westinghouse Electric Corporation.
The NRC has concluded that inspection schedules based on the Westinghouse recommendations will provide an acceptably high degree of assurance that turbine rotor discs will not be operated with cracks which could grow to a size that could cause disc failures.
We understand that the NRC Staff has discussed with Westinghouse the following clarification of the first criterion for turbine disc inspection contained in the safety evaluation report attached to your August 21 letter:
11 The initial inspection of a new rotor* or disc should be performed before any postulated (calculated) crack would grow to more than 1/2 the critical crack depth.
On the basis of our present knowledge of Westinghouse discs, we do not expect this interval will be much less than one fuel cycle or longer than two cycles unless and until these discs are fabricated and installed under conditions more favorable than in the past.
If the calculated interval is less than the scheduled first fuel cycle, the Licensee should seek Westinghouse's guidance on delaying the inspection until the refueling outage~ If the Aoo1
.s J/o 8109290301 810922 PDR ADOCK 05000266 G
PDR Mr. Harold September 22, 1981 calculated period is longei than the first fuel cycle, the Licensee should also seek Westinghouse's guidance for scheduling the first inspection at a later refueling outage.
Criterion #4 allows the inspection to be sooner or later (within the limits acceptable to Westinghouse) than the calculated date so as to coincide with a scheduled outage."
Since Wisconsin Electric is presentiy preparing to replace the presently installed Point Beach Unit 1 low pressure turbine rotors during the fall 1981 refueling outage with new replacement rotors which are fitted with new design discs which are much less susceptible to disc cracking than the old Westinghouse design, we believe our commitment to this clarified first criterion is more appropriate than a commitment to the first criterion as presented in the safety evaluation.
The remaining three criteria, Nos. 2 through 4, are acceptable as presented in the safety evaluation.
We therefore commit to the following inspection schedule criteria for low pressure turbine rotor inspection at Point Beach Nuclear Plant:
- 1.
New discs should be inspected in accordance with Westinghouse recommendations, or before any postulated crack would grow to more than 1/2 the critical depth.
- 2.
Discs previously inspected and found to be free of cracks or that have been repaired to eliminate all indications should be reinspected using the same criterion as for new discs, calculating crack growth from the time of the last inspection.
- 3.
Discs operating with known and measured cracks should be reinspected before 1/2 the time calculated for any crack to grow to 1/2 the critical crack depth.
- 4.
These inspection schedules may be varied to coincide with scheduled outages.
Westinghouse recommendations in this regard should be followed.
We trust these commitments. will satisfy your August 21 request.
We understand that these commitments will eliminate the need to report future turbine rotor disc inspection results to the NRC and will eliminate the need to transmit the computerized disc data sheets prepared by Westinghouse.
Copy to NRC Resident Inspector Very truly_ yours,
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Fay,~Director Nuclear Power Department