LOS ANGELES (AP) -- A Japanese company that manufactured the troubled steam generators at a key nuclear power plant in southern California might be looking for fixes with the wrong test equipment, U.S. federal regulators have disclosed.
A Nuclear Regulatory Commission report found that Mitsubishi Heavy Industries failed to verify that more than 1,000 tubes being used in a generator mock-up to explore potential repairs matched the specifications for tubing installed in the sidelined generators at the San Onofre nuclear power plant, which is located between Los Angeles and San Diego.
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 was abruptly shut down after a tube break released a trace of radiation.
The findings come as the U.S. agency plans to question officials Tuesday from plant's operator, Southern California Edison, about the company's proposal to restart one of the hobbled twin reactors, then run it at reduced power in an attempt to stop the vibrations that have been damaging tubes.
The NRC said Monday that a decision on that plan could come as soon as March.
Southern California Edison referred questions on the Japan inspection to Mitsubishi, which had no immediate comment.
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 that a gauge used to measure strain on tubing was not properly certified, NRC spokesman Victor Dricks said Monday.
The agency wants the company to explain how the problems occurred and when the issues can be corrected.
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 incorporated 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. They say the Mitsubishi analysis vastly misjudged how water and steam would flow in the reactors.
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 generators were replaced 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.
The plant is owned by SCE, San Diego Gas & Electric and the city of Riverside.