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.
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’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.
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.