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Office of Public Affairs, Region IV
611 Ryan Plaza Drive, Suite 400, Arlington TX 76011

No. IV-04-024   June 15, 2004
CONTACT: Victor Dricks
Phone: 817-860-8128

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The Nuclear Regulatory Commission has dispatched a team from its Region IV office in Arlington, Texas, to the Palo Verde Nuclear Generating Station to look into the causes of, and the plant response to, the shutdown of its three reactors at the site on June 14. An electrical grid disturbance has been identified as the initiating cause of the shutdowns.

Known as an Augmented Inspection Team (AIT), it will be charged with learning the facts surrounding the event at Palo Verde, which is located near Wintersburg, Arizona and operated by Arizona Public Service Co.

“Like all nuclear plants, Palo Verde uses off-site power. If that power source is interrupted, the plant is designed to shut down safely, which is exactly what occurred without any danger to public health or safety,” said Region IV Deputy Regional Administrator Thomas P. Gwynn. “However, because of some complications associated with the event, we want to take a detailed look at what occurred.”

Team members will arrive at the facility today. The team’s findings will be made public in an inspection report to be issued within 30 days of completion of on-site reviews.

At about 7:45 a.m. MST on June 14, all three Palo Verde reactors shut down automatically following a loss of off-site power. As they are designed to, four emergency diesel generators started up at Units 1 and 3 upon the interruption of off-site power. Those generators are designed to provide power to key safety systems and assist with the safe shutdown of the reactors. The loss of off-site power prompted the declaration of an Unusual Event at Units 1 and 3, the lowest level of emergency classification used by the NRC.

However, one of two emergency diesel generators at Unit 2 failed to start. Operators were able to safely shut down the reactor and cool it using power provided by the diesel generator that did start. However because only a single power source was available, the licensee declared an Alert at Unit 2. This is the second lowest of four levels of emergency classification used by the NRC. Shortly before 10 a.m. MST, off-site power was restored and the Alert was downgraded to an Unusual Event. The Unusual Event for all three units was terminated shortly after noon.

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Wednesday, October 20, 2010