ML19343B812

Advises of 801207-12 Reinsp of Low Pressure Turbine Rotor Discs for Indications of Keyway & Bore Cracks.Indications Noted on Two LP-1 Rotor Discs,As Found in Nov 1979 Insp. Rept Will Be Forwarded When Received from Westinghouse

ML19343B812
Person / Time
Site:	Point Beach
Issue date:	12/22/1980
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	Clark R, Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8012300593
Download: ML19343B812 (3)

Text

1 f1 Wisconsin Elecinc ecun courasr 231 W. MICHIGAN, P 0. BOX 2046. MitWAUMEE, WI $3201 December 22, 1980 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U. S. NUCLEAR REGULATORY COMMISSION Washington, D. C. 20555 Attention: Mr. R. A. Clark, Chief Operating Reactors Branch 3 Gentlemen:

DOCKET NO. 50-266 TURBINE ROTOR INSPECTION POINT BEACH NUCLEAR PLANT, UNIT 1 As discussed in response to item V of the enclosure to our letter dated March 19, 1980, the Point Beach Nuclear Plant Unit 1 low pressure turbine rotor discs were reinspected for indications of keyway and bore cracks during the refueling outage which began on November 26, 1980. This inspection was performed from December 7 to 12, 1980. The inspection utilized the ultrasonic tangential and radial aim technique described in the enclosure to our January 30, 1980 letter which reported on the first Point Beach Nuclear Plant Unit 1 turbine rotor disc inspection which was completed in November 1979. The Unit 1 turbine rotor discs were inspected from both the inlet and outlet sides of the discs, except for disc 6 which, because of the location of a balance ring on the outlet side, was only inspected on the inlet side.

As found during the first inspection, indications were noted on two of the twenty-four discs inspected. Both indications were in LP-1 rotor discs. Disc 42 on the governor end of LP-1 has an indication in one of the three keyways with a depth of 0.330 inches, an indicated growth of 0.080 in 7,174 on-line hours since the first inspection. Disc #3 on the governor end of LP-1 displayed a tangential aim indication in one of the three keyways. As during the first inspection, this indication CHD /

could not be confirmed with the use of the radial aim technique. 3 Since the radial aim technique has the capability of reliably /

detecting indications as shallow as 0.060 inches, we have ///

concluded that the indication in disc #3 at the governor end of LP-1 is below the normal detectable depth. The report for this inspection will be forwarded when received from Westinghouse Electric Corporation.

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1 Mr. Harold R. Denton December 22, 1930 Based on the present crack growth rate data from Westinghouse and the calculated critical crack size for this disc, we have conservatively estimated a minimum time to reach critical crack si=e for disc #2 governor end of 23 months. The details of this calculation are provided as Attachment 1 to this letter. The conservatively estimated time to reach critical size was calculated with the theoretical crack propagation time divided by three to account for uncertainties in the predictive process. As recommended by Westinghouse, we intend to reinspect the LP-1 92 and #3 governor end discs or replace the entire LP-1 rotor at our next refueling in approximately 11.5 months.

We have also conducted an inspection of the L-3 and L-4 blading and blade attachment in response to the manufacturer's recommendation. This inspection was unrelated to the turbine disc keyway inspection. Using magnetic particle techniques, i ten indications were found in the LP-1 #3 disc generator end between the L-4 blade row disc serrations. Eight blades were removed to permit grinding of the indications and six more blades were removed to permit insrallation of new style blades. As a result of blade removal, two additional indications were found

. between these disc serrations. All identified cracks were removed by grinding and blades reinstalled as recommended by the manufacturer. Six other indications were found by magnetic

] particle inspection and removed by grinding in the inlet seal area of the L-4 blade row on the #3 disc governor end on the LP-1 rotor. Six surface indications were also removed by grinding in the L-4 blade row disc serrations on the #3 disc generator end on LP-2 rotor. ,

f.

Point Beach Unit I will return to service on or.about December 29, 1980. Should you have any questions regarding these inspections, please contact us. -

Very truly yours,

~/

J

_ G ~

C. W. Fay, Director Nuclear Power Department Attachment Copies to: Mr. C. F. Riederer (PSCW)

NRC Resident Inspector

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N Attachment 1 POINT BEACH NUCLEAR PLANT UNIT 1 LP-1 Disc #2 Governor End Conditions: 497 MW load 132% overspeed 274*F keyway temperature Kie (Fracture Toughness) = 191.9 Ksi /In Bore Stress = 74.6 Ksi acr (Critical Crack = 1.98 in Depth from Keyway) at u (Indication Depth) = 0.330 UT Uncertainty Factor = 0.060 da/dt (Crack Growth = 3.14 x 10-5 hr in Rate)

Estimated Life (t)

.- .'-_ "cr (aut + 0.060) l 3 x da/dt

.' ,1.98 - (0.330 + 0.060) 3 x 3.14 x 10->

t = 16,879 x hrs or 23 months i

l Reinspection period [l/2 t) = 11.5 months i

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