ML19344D450
| ML19344D450 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 02/21/1980 |
| From: | Trammell C Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8003120407 | |
| Download: ML19344D450 (5) | |
Text
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Meeting Sumar.y for Point Beach I &2 /
Docket-Rilas
- Mr. Bruce Churchill, Esquire NRC PDL; LocaFPDR Shaw, Pittman, Potts and Trowbridge DRBI Reading 1800 M Street, 'i.W.
Washington, D. C.
20036 NRR Reading H. Denton E. Case Document Department University of Wisconsin D. Eisenhut Stevens Point Library R. pdesco Stevens Point, Wisconsin 54481 G. Zech Mr. Glenn A. Reed, Manager a
11 fiuclear Operations L. Shao Wisconsin Electric Power Conpany J. Miller Point Beach Nuclear Plant R. Vollmer 6610 fluclear Road T. J. Carter Two Rivers, Wisconsin 54241 A. Schwencer D. Ziemann P. Cneck G. Lainas D. Crutchfield
- 8. Grimes T. Ippolito R. Reid V. Noonan G. Knighton D. Brinkman Project Manager DELD OI&E (3)
C. Parrish/P. Kreutzer ACRS (16) liRC Participants NSIC TERA Licensee Short Service List 80 0312 0YO7
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- p WASHINGTON, D. C. 20555 4,., g.,o February 21, 1980 Docket Nos. 50-266 and 50-301 FACILITY
Point Beach Nuclear Plant, Units 1 and 2 LICENSEE:
Wisconsin Electric Power Company (WEPC0)
SUBJECT:
SUMMARY
OF MEETING HELD ON FEBRUARY 6, 1980 TO DISCUSS TURBINE DISC INSPECTIONS On February 6, 1980, the NRC staff met with representatives of Wisconsin Electric Power Company (WEPC0) and Westinghouse Electric Corporation (W) to discuss turbine disc inspection results on Unit 1 and future inspection plans for both units.
A list of attendees is contained in Attachment 1.
Highlights of the meeting are summarized below.
Point Beach Unit 1 shut down for annual refueling on Octot,er 5,1979.
As a result of turbine disc keyway cracking found at Surry, WEPC0 had the rotor discs (on the keyway side) of both low pressure (LP) turbines inspected by W during the October outage.
The opposite side of these discs was not inspected.
The results were that two discs had UT indications.
One, disc #2 on the governor end, had an indication at a keyway with a depth estimated to be.227.252".
The other, disc #3 on the governor end, had a small indication at a keyway, with no depth discernible but taken to be about 30 mils since it was below the magnitude of indication which can be reliably estimated as to depth.
WEPC0 has estimated that the time to reach critical flaw size is 73 months (see Attachment 2).
This period, divided by a factor of safety of 3, would allow for operation of up to 24 months without concern for removal of the two indications found.
W recommends that another inspection be conducted after 12 operating months following the initial inspection.
WEPC0 will arrange to have this followup inspection done in November 1980.
The information and proposed operations pending further inspection presented above were first discussed with the NRC staff at a steam generator meeting held on November 5, 1979.
WEPC0's disc fracture analysis used a keyway temperature of 274 F and computed a crack growth rate of 1.7 x 10-5 in/hr.
The critical crack size for the Point Beach rotor discs is 1.213 inches at 132% overspeed.
Point Beach Unit 1 is currently operating at reduced reactor coolant temperature (T
= 510 F) so
-thekeywaytemperatureisabout25FlowerthanassumedinthPanalysis.
The unit is also~being operated at reduced power (390 MWe or 78% power) as a result of the -lowered reactor coolant temperature.
2 Turbine overspeed trip protection consists of:
1.
Normal governor - 103% overspeed setpoint.
2.
Independent overspeed protection (safety grade) - 104% overspeed setpoint.
3.
Mechanical - 104.5% overspeed setpoint.
These are all tested at various intervals.
In addition, a crossover piping steam dump (to atmosphere) was installed in October 1974 to help limit turbine overspeed following a load rejection.
The turbine has no intercept valves.
The highest overspeed actually reached was 2340 rpm (130%), which occurred in 1972.
Following installation of the crossover dump valve, overspeed has been limited to 2215 rmp (123%).
Two years ago, WEPC0 experienced a disc failure on Oak Creek Unit 2, a coal-fired plant.
The turbine manufacturer was llis-Chalmers.
The disc was made of less tough material than the discs at Point Beach.
The failure was caused by a rim crack 170 mils deep.
The disc, weighing 14,000 pounds, broke into two pieces of about equal weight.
They broke through the turbine casing.
One piece continued through the turbine building wall and knocked a transformer askew, causing a transformer fire, and hit a nearby embankment.
WEPCO showed several photographs of the damage.
WEPC0 stated that they did not believe that another turbine inspection during an upcoming steam generator outage, as initially proposed by the NRC staff, would serve a useful purpose since they believe that any crack growth over this short period of time would not be detectable, i.e., within the band of uncertainty of the UT technique, and would not lead to any new conclusions.
WEPCO proposed instead to do a full inspection (both sides of all discs on both rotors, except for the outlet side of disc #6, wh ch cannot be inspected without removing these discs from the rotcrs with present methods) of the Unit 1 LP turbines in November 1980 Unit 2 would be inspected fully during the scheduled refueling commencing March 28, 1980.
At the conclusion of the meeting, following a staff caucus, we stated that:
Unit 1:
We agreed, based on present knowledge, that it is acceptable to run the unit until November 1980, at which time a full disc inspection should be made as proposed.
If an extended outage should occur before then, we may request WEPC0 to do a limited inspection of the one cracked disc.
We also stated that further information being developed from ongoing inspections at other plants could alter this conclusion.
Unit 2:
Tentatively, we agreed that this unit can be operated until the end of March 1980 as proposed, although the ratio of the postulated calculated crack size to the critical crack size for these discs is close to 1.
A complete turbine disc inspection as proposed should
3 be conducted then..This conclusion is also subject to change based on information being developed from the ongoing inspections.
(This turbine has not been inspected.)
We informed WEPC0 and W that a-Commission briefing on the subject of turbine disc problems is scheduled for Tuesday, February 12, 1980.
'L h
&$}H C. M. Trammell Attachments:
1.
List of Attendees 2.
Disc Fracture Analysis (Summary).
i
4 h
LIST OF ATTENDEES POINT BEACH TURBINE MEETING FEBRUARY 6, 1980 Nuclear Regulatory Commission
'C. Trammell W. Hazelton
'W.
Ross R. Licciardo-1 H. Walker C. Kieffer D. Sellers R. Hermann P. Boehnert (ACRS staff)
R. Klecker W. Collings K. Hoag Wisconsin Electric G. Frieling D. Porter C."W.
Fay R. Menning S. Burstein (conclusion only)
Westinghouse J. Schmerling E.-Johnson Other J. O'Neill (Shaw, Pittman, Potts & Trowbridge)
G. Charnoff (Shaw, Pittman, Potts & Trowbrid e) 0 J.-Kenrick (Eckert,.Seamans)
- 5. Bush (Battelle-Northwest)
J. Weeks (Brookhaven) 1
~
RHacknt x POINT BEACH NUCLEAR PLANT, UNIT 1 TURBINE ROTOR DISC FRACTURE ANALYSIS 497 MWe 132% OVERSPEED LP.-l DISC #2 GOVERNOR END Klc-(FRACTURE TOUGHNESS) = 171 KSI/IN.
at (INDICATION DEPTH) = 0.250 IN.
u a t + 0.060 (UT UNCER JTY FACTOR) = 0.310 IN.
u acr (EFFECTIVE CRITICAL CRACK DEPTH) = 1.213 IN.
acr - a t = 0.903 IN.
u Tg (KEYWAY TEMPERATURE) = 274*F da/dt (CRACK GROWTH RATE) = 1.7 x 10-5 IN./HR.
ESTIMATED TIME TO REACH CRITICAL CRACK SIZE = 73 MONTHS ADDITIONAL S AFETY FACTOR = 3 WESTINGHOUSE ESTIMATED LIFE = 24.3 MONTHS WISCONSIN ELECTRIC INSPECTION INSERVAL = 12 MONTHS e
6 a W