A Japanese company that manufactured the troubled steam generators at the San Onofre nuclear power plant might have been looking for fixes with the wrong test equipment, federal regulators said.
Mitsubishi Heavy Industries failed to verify more than 1,000 tubes used in a generator mock-up to explore potential repairs matched specifications for tubing installed in the sidelined California generators, according to a Nuclear Regulatory Commission (NRC) report.
Excessive wear to tubing that carries radioactive water has been at the heart of problems at San Onofre, which hasn’t produced electricity since January, after the plant abruptly shut down after a tube break released a trace of radiation.
Those finding came as the agency questioned officials Tuesday from operator Southern California Edison (SCE) about the company’s proposal to restart one of the hobbled twin reactors, then run it at reduced power in an attempt to stop vibration that has been damaging tubes.
The NRC said a decision on that plan could come as soon as March.
Government records show the NRC issued a “notice of nonconformance” on Nov. 30 after inspectors visited a Mitsubishi plant in Kobe, Japan.
In addition to questions about the tube specifications used in tests, inspectors also found a gauge used to measure strain on tubing did not have the proper certification, NRC spokesman Victor Dricks said Monday.
The agency wants the company to explain how the problems occurred and when they can correct the issues.
The federal inspection came as Mitsubishi was preparing to use results of the testing done on the mock-up generator in other research, the report said. That raises the possibility that potentially flawed work could have been involved in other testing.
Earlier this year, federal officials blamed a botched computer analysis for design flaws that are largely to blame for unprecedented wear in tubes at the plant, located between San Diego and Los Angeles. They say the Mitsubishi analysis vastly misjudged how water and steam would flow in the reactors.
SCE referred questions on the Japan inspection to Mitsubishi, which had no immediate comment.
Gradual wear is common in steam generator tubing, but the rate of erosion at San Onofre startled officials because the equipment is relatively new. The company replaced the generators in a $670 million overhaul and began operating in April 2010 in Unit 2 and February 2011 in Unit 3.
Overall, records show investigators found wear from friction and vibration in 15,000 places, in varying degrees, in 3,401 tubes inside the plant’s four generators, two in each reactor.
SCE, San Diego Gas & Electric and the city of Riverside own the plant.