Palo Verde nuclear plant still ran after backup equipment exploded via AZ Central

For 57 days last year and early this year, one of the nuclear reactors at the Palo Verde Nuclear Generating Station west of Phoenix kept running after an explosion knocked a backup generator out of service.

Experts at the Nuclear Regulatory Commission disagreed strongly over whether the plant should have been allowed to keep running during the repairs, according to documents leaked to the Union of Concerned Scientists, a watchdog group.

The NRC usually allows a nuclear plant 10 days to make such repairs. In this case, the agency granted the plant’s operator, Arizona Public Service Co., two extensions. NRC officials said the decision came after a careful review of the risks.

But not everyone at the agency agreed with the decision. NRC employees filed three dissents that were given to The Arizona Republic by the scientist watchdog group. The NRC subsequently released one of the documents, a petition asking for the time extensions to be revoked.

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Each of Palo Verde’sthree reactors has two emergency generators and multiple layers of protection to keep water flowing over the radioactive fuel in the event any equipment fails.

The trouble began Dec. 15 when one of Unit 3’s generators exploded during a routine test. APS discussed repairs five days later with the NRC, and regulators extended to 23 days the time allowed before the plant would have to shut down. A second extension allowing for 62 days of repairs and tests was granted in January.

The backup generator was out of service from Dec. 15 to Feb. 9.

The dissenting documents said both extensions were unusual, especially the second one.

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Burnell said APS and its parent company, Pinnacle West Capital Corp., did not pressure the NRC to approve the extensions for financial reasons.

“The NRC’s decision regarding the Palo Verde extension request was based solely on an appropriate review of the plant’s technical justification,” Burnell said.

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David Lochbaum, director of the nuclear safety project at the Union of Concerned Scientists, questioned whether the FLEX equipment could have restored power soon enough to prevent the fuel from overheating.

He also said that the inconsistency between the D.C. Cook event and Palo Verde doesn’t make sense.

“Using the same process and procedures to reach totally different outcomes means one outcome was wrong,” Lochbaum said. “So was the NRC wrong at Cook  or wrong at Palo Verde?”