Seeking to avoid costly increased scrutiny from the Nuclear Regulatory Commission, Arizona Public Service officials said Tuesday they are improving the performance of the Palo Verde Nuclear Generating Station west of Phoenix.
They admitted violations of NRC regulations when a backup emergency diesel generator failed at Unit 3 in September, the latest in a series of problems at the plant.
But they said the violations were not serious enough to warrant increased oversight.
At a conference between NRC and APS officials Tuesday, several NRC officials disagreed, saying said they believe the backup diesel generator problem at Palo Verde raises serious safety issues.
“Diesel generators are critical features of defense in depth,” said Art Howell, director of the division of reactor projects in the NRC’s region 4, which includes Arizona.
“There have been untimely failures in the past at Palo Verde. Unfortunately, this is another example, suggesting that the efforts to date (to correct the operating problems) have not been effective.”
In other recent problems, Unit 1 had an unscheduled outage in October, and a scheduled refueling outage at Unit 2 lasted longer than expected last fall. In December, the NRC complained of “egregious” errors for more than a decade in mixing chemicals at Palo Verde spray ponds, which were intended to control corrosion of safety components but led to deposits on tubes that caused insulation and heat-transfer problems.
Last week, the company announced the appointment of a new chief nuclear officer to try to turn the plant around.
In the latest issue, the NRC said the Unit 3 emergency generator operated in an unreliable condition for 40 days last summer and was inoperable for 18 days in September.
The backup generator provides electricity to keep critical equipment running if the unit loses its connection to the outside power grid. Each of the units has two backup diesel generators and banks of batteries to provide power in an emergency, according to APS.
An investigation found the cause of the problem was the failure of an electrical relay. An initial fix in July failed to correct the root cause of the problem, leading to the failure during a test in September.
APS officials said they are strengthening troubleshooting procedures to improve the plant’s reliability.
“We continue to implement, reinforce, monitor and adjust our performance improvement plan to provide greater confidence that similar events will not recur,” said David Mauldin, APS vice president of nuclear engineering and support.
If the regulators determine the latest violations were a significant safety issue, APS faces increased inspections, more public meetings on the plant’s operating condition and more meetings with the board of directors of Pinnacle West Capital Corp., the utility’s parent company, NRC spokesman Victor Dricks said.
Only one other nuclear plant in the U.S. is operating under those conditions, he said,
“It would probably take several years to deal with the requirements that would be imposed,” Dricks said, adding that the costs to APS would be substantial.
But he added that APS would not be required to shut down the plant, which supplies to electricity to utilities in Arizona, New Mexico, California and Texas.
The NRC technical staff probably will make its decision in about 30 days, Dricks said.
Heather Murphy, spokeswoman for the Arizona Corporation Commission, which regulates APS rates, said the commissioners probably would not allow APS to pass on additional regulatory costs to customers if the NRC determines the problems were the fault of APS.
APS has a 20 percent, $434 million rate increase pending before the commission to recover past cost increases, primarily the higher price of natural gas fuel.