ML20031D315
| ML20031D315 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 10/05/1981 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8110130238 | |
| Download: ML20031D315 (2) | |
Text
t W
Northem States Power Company 414 Nicollet Mall Minneapoks. Minnesota 55401 Tetephone <612) 330-5500 9
Octcber 5, 1981 g aGb *c.
Director of Nuclear Reactor Regulation p
g g jggg -jj i.
U S Nuclear Regulatory Commission Washington, JC 20555
"'Wdida ge 9
PRAIRIE ISLAND NUCLEAR GENERATING PLANT Docket No. 50-282 License No. DPR-42 Cu ]
Docket No. 50-306 License No. DPR-60 Resolution of Turbine Disc Cracking Issue Reference 1: Letter from D G Eisenhut (NRC) to L 0 Mayer (NSP) dated February 25, 1980 Reference 2:
Letter from L 0 Mayer (NSP) to Director of NRR (NRC) dated ticrch 19, 1980 Reference 3.-
Letter from R A Clark (NRC) to L 0 Mayer (NSP) dated September 1, 1981
'With respect to the r.urbine disc cracking issue, Reference 1 requested that the licensee submit 'information ou turbine disc materials, the results of inspecticas of LP turbine rotors, further inspection plans, water chemistry conditians, rbine missile analyses.
Reference 2 provided information in respons<
tRC request and stated "Upon receipt from Westinghouse of reanalysts t'o t Prairie Island Units 1 and 2 of missile energies, velocities, and degree of containmont within the turbine shell, NSP will have the Architect / Engineer re-run the licensing basis missile analysis, utilizing the new parameters".
Following receipt of missile energy information from Westinghouse, an analysis of the probability of damage to safeguard equipment from turbine missiles was conducted following the guidelines contained in the NRC Standard Review Plan.
Calculations were performed for inspection intervals o f 1,2,3,4,5 and 10 years. The analysis concluded that an inservice inspecttonintervaloffgeyears for the turbine discs meets the probability of damage criteria of 10 contained in Standard Review Plan 2.2.3.
A plot of inspection interval versus probability of damage indicates that the
~#
10 probability figure corresponds to an inspection interval of 7.1 yeara. An inspection schedule of five years is consistent with Westinghouse recommendations and NRC's past prac t ice s.
m 8110130238 811005 PDR ADOCK 05000282 G
~
1 NORTHERN CTATE'3 POWER COMPANY Director of Nuclear Reactor Regulation october 5, 1981 Page 2 Reference 3 requested that NSP commit to the use of four criteria, contained in the safer; evaluation accompanying the September 1, 1981 NRC letter, for fvture disc inspections.
NSP is agreeable to following the inspection e hadule criteria as follows:
- 1. New discs will be inspected at the first refueling outage following installation, or before any postulated crack would grow to more than one-half the critical depth.
- 2. Discs previously inspected and found to be free of cracks or that have been repaired to eliminate all indications will be re-inspected using the same criteria as for new dir *. calculating crack growth from the time of last inspect ion.
- 3. Discs operating with known and measurec cracks will be re-inspected before one-half the time calculated for any crack to grow to one-half the critical crack depth.
- 4. These inspection schedules will be varied as necessary to coincide with scheduled outages. A normal inspection frequency of five years will be utilized.
Based on the results of the turbine missile analysis and NSP'S commitment to the criteria for inspection intervals, we believe that the turbine disc cracking issue has been satisfactorily resolved with respect to the Prairie Island Westinghouse turbines.
L ^* r' e s-L 0 Mayer, PE Manager of Nuclear Support Se rvices LOM/bd cc: J G Keppler G Charnoff NRC Resident Inspector
~gn
,n,
-.-,u
- p.,, -,
,- n -+--
-m--,..e,-
a a--a w
-a,.
. - - -