ML19253A149

Notification That,Due to Unscheduled Cold Shutdown Required to Repair Cracked Weld in Nonisolable Steam Line, Change in Scheduled Replacement of safety-related Transformers Is Required

ML19253A149
Person / Time
Site:	Millstone
Issue date:	08/09/1979
From:	Counsil W NORTHEAST UTILITIES
To:	Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
NUDOCS 7908160428
Download: ML19253A149 (2)

Text

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HARTFORD. CONNECTICUT 06101 e

(203) 666-6911 k L 2 August 9, 1979 Docket No. 50-336 Mr. V. Etello, Jr.

Director Office of Inspection and Enforcement U. S. Nuclear Regulatory Commission Washington, D. C. 20555

References:

(1) W. G . Counsil letter to R. H. Crier dated June 15, 1979.

(2) W. G. Counsil letter to V. Stello, Jr., dated July 13, 1979.

Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Load Center Transf ormers In References (1) and (2), Northecst Nuclear Energy Compt y (NNECO) advised the NRC Staff of recent experiences involving dry-type 4160/4J0 V load center trans-formers. The details of the specific problems involving three dif ferent trans-formers, along with the schedule for affecting replacement of the safety-related transformers of Millstone Unit No. 2, were provided.

Since the date of Reference (2), events affecting plant availability have occurred.

Specifically, an unscheduled cold shutdown is required to affect repair of a cracked weld in a non-isolable steam line. The purpose of this letter is to document the resulting change in the scheduled replacement of the safety-related transformers, as discussed verbally earlier today with the NRC Staff.

One c; the two safety-related transformers will be replaced with a fully qualified transformer from a different vendor prior to resuming plant operation from the current shutdown. Replacement of the second transformer, which is a refurbished unit from the original vendor, is scheduled for a planned outage beginning no later than October 6, 1979. Effectively, the outage activities originally planned for the September 1 outage are being completed in two phases, either during the current shutdown or the one tentatively scheduled for October 6, 1979. This is acceptable from a safety perspective in that the subject transformers are operated continuously and operability requirements are detailed in current Technical Spec if icat ions. NNECO has concluded that with the replacement of the first trans-former, additional assurance regarding operability of AC power sources is provided to justify continued, safe plant operation until the second replacement can be affected. The qualification documentation for the second transformer is currently being assembled, and will be available before the replacement is completed.

801 217 79081609ELI /

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. Post removal inspection of tt'e transformers being replaced is e::pected to further the level of understanding regarding failure mechanism.

We trust the above information is sufficient to clarify our revised replacement program.

Very truly yours, NORTIIEAST NUCLEAR ENERGY COMPANY

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W. G. Coun'sil Vice President 801 218