ML19257D782

Forwards Low Pressure Disc Ultrasonic Insp Rept, Prepared by Westinghouse

ML19257D782
Person / Time
Site:	Point Beach
Issue date:	01/30/1980
From:	Fay C WISCONSIN ELECTRIC POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
Shared Package
ML19257D783	List: ML19257D782 ML19257D784
References
NUDOCS 8002060434
Download: ML19257D782 (2)

Text

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0 Wisconsin Elecinc rowca cournur 231 W. MICHIGAN, P.O. BOX 2046. MILWAUKEE, WI $3201 January 30, 1980 Mr. Harold R.

Denton, Director Office of Nuclear Reactor Regulation U. S. NUCLEAR REGULATORY COMMISSION Washington, D.

C.

20555 Attention:

Mr. A.

Schwencer, Chief Operating Reactors Branch 1 Gentlemen:

DOCKET NO. 50-266 TURBINE ROTOR INSPECTION POINT BEACH NUCLEAR PLANT, UNIT 1 As promised in our letter to Mr. Schwencer dated January 7, 1980, we are submitting, as Attachment A to this letter, the report and analysis of the October 22 through November 2, 1979 low pressure turbine rotor inspection at Point Beach Nuclear Plant, Unit 1.

This inspection was performed by Westinghouse Electric Corporation personnel using the ultrasonic techniques and equipment described in the report.

As discussed in the report, two indications were identi-fied during this inspection.

One indication, approximately 0.250 inches deep, was found in the #2 disc on the governor end of the LP-1 turbine rotor.

This indication is located at the keyway apex.

The second indication was found on the #3 disc on the governor end of the same LP-1 turbine rotor.

This indication is located close to the keyway apex and is smaller than the normal detectable depth.

The normal detectable depth, as identified by Westinghouse, is 0.020 to 0.030 inch.

The remaining eighteen discs inspected showed no indications of any defects.

The defect identified in disc #2 is the limiting factor for determining the future in-service inspection interval for the Unit 1 rotor discs.

An analysis based upon conservative crack growth rate data has been performed.

The parameters associated with this analysis of the LP-1 disc #2 are shown on Attachment B.

The crack growth rate of 1.7 x 10-5 inch / hour is based on the total Westinghouse experience to date and the 3% Ni, Cr, Mo, V alloy discs from the British experience previously discussed with the NRC Staff by Westinghouse.

7 5

}929 80 02 06 0 +3 +

Mr. Harold R.

Denton January 30, 1980 The analysis performed by Westinghouse indicates that a conservative estimate of the time required for the disc #2 indicated defect to reach the critical crack size, if it propagates, is approximately 73 months operating at full load and based upon a maximum turbine overspeed of 132%.

This conservative estimate is further modified by an additional factor of safety of 3 to arrive at the Westinghouse opinion that the estimated remaining life of disc #2 is 24 months.

Further conservatism is added by the recommendation that disc #2 be re-examined within 12 months.

As requested in the attachment to your December 27 letter, Attachment C provides the critical crack size in the bore in a format similar to that presented in the Westinghouse letter dated December 20, 1979.

This attachment presents a ratio of calculated bore cracks to the d';c bore critical crack depth based on the observed Zion 1 crack growth rate and the estimated operating hours through December 1980.

The largest ratio is 0.58, indicating that the unit can be safely and conservatively operated through December 1980.

Your letter also requested that we provide our current assessment of turbine missile consequences both at 1800 RPM and 132% overspeed.

Topical Report WCAP-7525, June 1970, presents a discussion of the likelihood and consequences of turbine over-speed at the Point Beach Nuclear Plant.

As you know, Westinghouse is presently investigating turbine missile energies based on a revised analysis of the turbine missile impact with the turbine casing.

When the results of this investigation become available, we will examine the analysis and determine whether our current assessment, as presented in this WCAP, should be revised.

We will, of course, inform you of any changes which result from our review of the Westinghouse analysis which would affect our turbine missile assessment.

In conclusion, based on the results of the October 1979 inspection and the conservative minimum estimated operating life calculations presented in the attachments to this letter, we have determined that Point Beach Nuclear Plant Unit 1 can be safely operated during the present operating cycle.

We are planning to inspect the Unit 1 discs again during the Fall 1980 outage to determine whether there has been a change in the condition of the LP turbine rotors.

At that time, the discs will be inspected from both sides.

We firmly believe that an additional inspection prior to that time is not warranted and would not serve any useful purpose.

We look forward to discussing this subject further and answering any questions you may have during our scheduled meeting on 3979 325 February 6, 1980.

Very truly yours, C. W.

Fay, Director Nuclear Power Department Attachments