ML16342A242

Provides Comments on Interim Rept on Potential for Inadequate Electrical Isolation in Certain 120-V AC Power Circuits for Plant,Submitted by Util Ltr

ML16342A242
Person / Time
Site:	Diablo Canyon
Issue date:	09/08/1993
From:	Peterson S Office of Nuclear Reactor Regulation
To:	Rueger G PACIFIC GAS & ELECTRIC CO.
References
TAC-M86227, TAC-M86228, NUDOCS 9309150330
Download: ML16342A242 (8)

Text

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UNITEDSTATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 September 8,

1993 Docket Nos.

50-275 and 50-323 Mr. Gregory M. Rueger Nuclear Power Generation, B14A Pacific Gas and Electric Company 77 Beale Street, Room 1451 P.O.

Box 770000 San Francisco, California 94177

SUBJECT:

POTENTIAL FOR INADEQUATE ELECTRICAL ISOLATION IN CERTAIN 120-V AC POWER CIRCUITS FOR DIABLO CANYON POWER PLANT, UNIT NO.

1 (TAC NO. M86227)

AND 2 (TAC NO. M86228)

By letter dated April 6, 1993, Pacific Gas and Electric Company (PG&E) submitted an interim report on the potential for inadequate electrical isolation in certain 120-V ac power circuits for PG&E Class IA and IBI instrumentation.

PG&E established a Review Project for Diablo Canyon Power Plant (DCPP) to review the design of the post accident monitoring instrumentation to determine if the instrumentation attributes met those specified in Regulatory Guide (RG) 1.97.

,During these

reviews, the licensee found that parts of the safety-related instrumentation had the potential to deviate from the single-failure criterion because of potentially inadequate electrical isolation in certain 120-V ac power circuits.

We understand your review effort is continuing and the interim report you submitted was to ensure that the format and text of the report are acceptable.

We have reviewed your interim report and have the following comments:

Of the credible events (i.e., seismic activity, fire, harsh post accident environments, flooding, tornadoes and tsunamis) that could cause the postulated common-mode failure (electrical shorting) in the unisolated

devices, PG&E considered only seismic events and fire protection.

The interim report did not adequately explain why other credible events were not considered.

~

-The analyses of evaluations of seismic events and fire protection in the interim report did not provide adequate detail to enable the reviewer to reach the same conclusion as that of PG&E.

In particular, the final report should have more data of the seismic evaluations that confirmed single-failure tolerance of the identified circuit pairs and why, in the event of a postulated fire, absence of electrical isolation would not impact the availability of Appendix R 120-V ac circuits.

The interim report indicated the 120-V ac'power circuits analyzed so far did not deviate from the single-failure criterion.

We understand that you will PDR ADOCK"05000275 1

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<<E, Hr. Gregory H. Rueger September 8,

1993 complete your review and submit, to the staff, the final report for the electrical isolation issue by the end of 1994.

The final report should provide sufficient detail for the, staff to complete an in-depth review.

This action closes TAC Nos.

H86227 and H86228.

Sincerely, cc:

See next page DISTRIBUTION:

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TQuay 93 OFFICIAL RECORD COPY DOCUMENT NAME:

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Hr. Gregory H. Rueger complete your review and submit, to the staff, the final report for the electrical isolation issue by the end of 1994.

The final report should provide sufficient detail for the staff to complete an in-depth review.

This action closes TAG Nos.

H86227 and H86228.

Sincerely, cc:

See next page Sheri R. Peterson, Project Hanager Project Directorate V

Division of Reactor Projects III/IV/V Office of Nuclear Reactor Regulation

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Mr. Gregory M. Rueger Pacific Gas and Electric Company Diablo Canyon CC:

NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission P. 0.

Box 369 Avila Beach, California 93424 Dr. Richard Ferguson, Energy Chair Sierra Club California 6715 Rocky Canyon Creston, California 93432 Ms. Nancy Culver San Luis Obispo Mothers for Peace P. 0.

Box 164 Pismo Beach, California 93448 Ms. Jacquelyn C. Wheeler 3303 Barranca Court San Luis Obispo, California 93401 Managing Editor The County Telegram Tribune 1321 Johnson Avenue P. 0.

Box 112 San Luis Obispo, California 93406 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo, California 93408 Mr. Truman Burns Mr. Robert Kinosian California Public Utilities Commission 505 Van Ness, Rm.

4102 San Francisco, California 94102 Diablo Canyon Independent Safety Committee ATTN:

Robert R. Wellington, Esq.

Legal Counsel 857 Cass Street, Suite D

Monterey, California 93940 Mr. Steve Hsu Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento, California 94234 Regional Administrator, Region V

U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Mr. Peter H. Kaufman Deputy Attorney General State of California 110 West A Street, Suite 700 San Diego, California 92101 Christopher J.

Warner, Esq.

Pacific Gas 5 Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. John Townsend Vice President and Plant Manager Diablo Canyon Power Plant P. 0.

Box 56 Avila Beach, California 93424

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