United States Nuclear Regulatory Commission - Protecting People and the Environment

Degraded Switchyard Voltage Issues at Palo Verde Nuclear Generating Station Units 1, 2, and 3

March 22, 1999

MEMORANDUM TO: William D. Travers
Executive Director for Operations
FROM: John T. Larkins, Executive Director Advisory Committee on Reactor Safeguards


During the 460th meeting of the Advisory Committee on Reactor Safeguards, March 10-13, 1999, the Committee considered the February 16, 1999, letter from Arizona Public Service (APS) Company to you commenting on the statement made by the Committee in its letter dated November 23, 1998, regarding the Reprioritization and Proposed Resolution of GSI-171, "Engineered Safety Features Failure From Loss-of-Offsite-Power Subsequent to a Loss-of-Coolant Accident." In its letter, the Committee stated "NRR has raised concerns that degraded switchyard voltage events at Salem and Palo Verde nuclear plants indicate it is possible that plants have either not implemented under-voltage protection properly or conditions have changed that invalidate original design basis capability." This statement was quoted from the background information (Ref. 3) provided by the staff during the Committee's review of the proposed resolution of GSI-171.

The ACRS letter points out the NRR concerns stemming from the degraded switchyard voltage events and does not imply that Palo Verde has not implemented the under-voltage protection properly. Since ACRS does not plan to pursue this issue, additional information from, or a meeting with, APS is not necessary. The Committee suggests that the staff respond to the APS letter by clarifying the intent of the statement quoted in the ACRS letter.

The Committee would like to be kept informed of the staff's response to APS.


  1. Letter dated February 16, 1999, from James M. Levine, Arizona Public Service, to Nuclear Regulatory Commission, Subject: Palo Verde Nuclear Generating Station (PVNGS), Units 1, 2, and 3, Degraded Switchyard Voltage Issues at PVNGS.
  2. Letter dated November 23, 1998, from R. L. Seale, Chairman, ACRS, to William D. Travers, Executive Director for Operations, NRC, Subject: Reprioritization and Proposed Resolution of Generic Safety Issue-171, "Engineered Safety Features Failure From Loss-Of-Offsite-Power Subsequent To A Loss-Of-Coolant Accident."
  3. Memorandum dated August 18, 1998, from Charles E. Rossi, Office for Analysis and Evaluation of Operational Data, NRC, to John W. Craig, Office of Nuclear Regulatory Research, NRC, Subject: Request For Review of the Re- prioritization of GSI-171, "Engineering Safety Features Failure From A Loss-Of- Offsite Power Subsequent to a Loss-Of-Coolant Accident."

cc: A. Vietti-Cook, SECY
J. Blaha, OEDO
J. Mitchell, OEDO
S. Collins, NRR
A. Thadani, RES

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