The agency said Monday that the utility changed a method it used to evaluate the design of several Diablo Canyon plant components without adequate justification to the agency. The components were reactor vessel heads and steam generators.
The utility recognized the mistake in 2013 and made revisions.
Utility spokesman Blair Jones said PG&E used a method approved by the NRC, but it was not sufficiently documented. The violation did not challenge the seismic safety of the plant, Jones said.
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“While PG&E has subsequently demonstrated that prior NRC approval was not required, the NRC has determined that a violation should be issued to PG&E for not adequately documenting this in 2013,” he said. “This violation is of very low safety significance and does not challenge the seismic safety of the facility.”
The last violation issued by the NRC against Diablo Canyon was last year and involved the plant’s emergency evacuation planning. From 2005 to 2013, the emergency plan lacked a requirement to evacuate boats at sea within 10 miles of the plant in the event of a radioactive release.