Palo Verde nuclear plant still ran after backup equipment exploded

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.

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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.

"The NRC's action is inconsistent with the NRC mission, NRC vision, NRC safety objectives, NRC regulatory effectiveness strategies, NRC openness strategies and the principles of good regulation," said Roy Mathew, a longtime agency employee, in his Jan. 23 petition to his employer.

Mathew has held various engineering jobs at the NRC since joining in 1988, according to a bio with the NRC.

The two other dissents leaked to the scientists are known as Differing Professional Opinion documents and were written by NRC employees whose names were redacted. The NRC said it is still reviewing them and has not released them to the public.

"The NRC reached its technical decision regarding Palo Verde’s request separately from its consideration of the DPO," said Scott Burnell from NRC's office of public affairs. "The DPO process continues at this point."

Dissenter: Extensions were unusual

Nuclear plants operate with what officials call layers of safety.

Each of Palo Verde's three 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.

Mathew noted that the agency denied a similar request from the D.C. Cook Nuclear Plant in Michigan because the staff determined the plant couldn't mitigate accidents during that extended time.

He said in his petition that it is unclear why a different decision was made for APS.

"I am not sure whether the loss of revenue for the utility had any influence on the NRC decision to approve these license amendments," he wrote. "I did not find any safety reason for NRC to approve these license amendments."

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.

Safer to keep reactor running or shut it down?

Among Mathew's concerns were that if the nuclear plant lost power from the grid and had a similar failure in its other diesel generator, it would not have been able to cool nuclear fuel in a timely manner. If the fuel can't be cooled, it can lead to radiation releases.

APS officials said there was no increased threat or reduction in the safety margin because of the decision to keep the unit running.

They said their analysis showed it was safer to keep the unit running and minimize activity around it, such as other routine tests and maintenance, than to initiate a shutdown, which involves a variety of complicated procedures such as moving fuel rods.

"People that have studied risk and know how to use risk to make better decisions know this is the direction we need to be gong to make this industry safer," said Bob Bement, executive vice president and chief nuclear officer at Palo Verde. "The fact the NRC approved it, they knew they had people in the agency that don't support this."

Bement said that even in the worst-case scenario involving additional failures of equipment, APS was prepared to keep the plant's fuel cool. And even in an unthinkable situation where multiple pieces of backup equipment failed, any radiation would be contained within the concrete dome of the plant, not released where it could threaten public health.

In deciding to allow Palo Verde to keep running the unit, the NRC cited the fact that APS had connected three portable generators to the unit. These portable units, called FLEX equipment, were ordered industry-wide following the 2011 nuclear meltdown in Japan.

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?"

Decisions made on case-by-case basis

Lochbaum emphasized that his organization is not anti-nuclear power. The group does, however, advocate for the safest possible operation of the country's nuclear fleet.

Burnell, from the NRC, could not say whether it will be the agency's policy going forward to allow longer repair times for such failures.

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"The NRC always bases its decisions on the technical justifications supporting a given request," he said. "If a U.S. plant uses post-Fukushima procedures and resources in justifying a request to extend allowable repair times, the NRC will carefully review the justification and reach a regulatory decision that protects public health and safety."

A special NRC inspection team visited the power plant in February to better understand why the generator exploded.

"The team determined that operator response was appropriate and neither caused nor contributed to the failure," said the now-public inspection report. "The team did not identify any performance deficiencies or violations of NRC requirements as a result of this special inspection."

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