The Diablo Canyon nuclear power plant in San Luis Obispo County was inspected three months before a leak caused an eight-day shutdown, a report found.
The Diablo Canyon nuclear power plant in San Luis Obispo County was inspected three months before a leak caused an eight-day shutdown, a report has found. (Joe Johnston / San Luis Obispo Tribune file photo)

The U.S. Nuclear Regulatory Commission didn’t properly inspect equipment at Diablo Canyon, just months before a leak in its once-through cooling system shut down the nuclear power plant, according to a new report.

On Monday, the U.S. Office of the Inspector General released an event inquiry report detailing findings on the NRC’s oversight of the Diablo Canyon nuclear power plant in San Luis Obispo County. The OIG regularly conducts audits and investigations of NRC programs and operations.

According to a news release on the report, the OIG received multiple allegations of improper oversight at Diablo Canyon in recent years, including problems with the NRC’s oversight of safety-related structures, systems and components.

One of those is the plant’s auxiliary feedwater system (AFW), which acts as a backup water supply to cool the reactor if normal feedwater is out of service.

In July 2020, a leak in the AFW system shut down the plant for eight days, prompting allegations that the NRC had inadequately inspected the system before the event.

In the report released Monday, the OIG said its investigation into the incident found that the NRC “failed to identify piping insulation on the AFW system that had long been in a degraded condition, and that led to a leak.”

According to the report, the NRC had not inspected the area where the leak occurred, even though its inspection report said inspectors had performed a complete physical inspection of the system in April of that year — just three months before the leak being discovered. The investigation also found that NRC staff spent fewer hours inspecting the plant’s AFW systems than is recommended.

The OIG says PG&E, which operates the plant, has since remedied the AFW system failure and made improvements. Diablo Canyon continues to operate safely, according to the report.

PG&E spokeswoman Suzanne Hosn said, “Safety is and always will be our most important responsibility at PG&E and Diablo Canyon, and the plant has an excellent safe operating record.”

“We identified this issue while Unit 2 was shut down for maintenance in 2020, made the repairs and conducted thorough inspections before the unit was returned to service,” she wrote in a statement to The Tribune on Monday. “Additionally, we performed similar inspections on Unit 1 and identified no further conditions requiring repair. We take issues about safety very seriously and take immediate actions to ensure we are always ready to meet our mission to protect public health and safety.”

Congressman Responds to Diablo Canyon Report

Congressman Salud Carbajal, whose district includes Diablo Canyon, called the findings “unsettling and unacceptable.”

“The safety and well-being of the entire San Luis Obispo community relies on federal inspectors adhering to those safety protocols, and the negligence detailed in this report will erode the public trust in those who are tasked with keeping us safe,” he said in a statement. “It is critically important that the NRC make a clear and convincing case to the Central Coast how it will hold their inspectors accountable for breaking protocol and how it intends to restore confidence in their operations at (Diablo Canyon).”

Carbajal said that in the coming days, he plans to formally ask NRC leaders for specific details on why required inspections were not completed, the corrective actions to be taken and how the regulatory commission will enforce it procedures in the future.

When reached for comment Monday evening, Victor Dricks, senior public affairs officer for the NRC, said that “the NRC continues to have full confidence in its staff and their commitment to our important nuclear safety mission.”

“We are reviewing the inspector general’s report and will take appropriate action if needed,” Dricks said. “At no time was public safety endangered because of this incident.”

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