By Associated Press, Published: July 19AP

LOS ANGELES — Federal regulators Thursday concluded that the operator of the San Onofre nuclear power plant in California did not mislead the government about modifications to its troubled steam generators, where unusual damage has been found on scores of tubes that carry radioactive water.

Environmental activists had accused Southern California Edison of duping the Nuclear Regulatory Commission about a series of changes to the massive machines before they began operating in 2010 and 2011, including boosting the number of tubes and redesigning internal supports that hold them in place.

The generators, which resemble massive steel fire hydrants, are one of the central pieces of equipment in a nuclear plant. At San Onofre, each one stands 65 feet high, weighs 1.3 million pounds, with 9,727 U-shaped tubes inside, each three-quarters of an inch in diameter.

The tubes are one of the barriers between the radioactive and non-radioactive sides of the plant. If a tube breaks, there is the potential that radioactivity could escape into the atmosphere. Serious leaks also can drain cooling water from a reactor.

The steam generators were manufactured by Japan-based Mitsubishi Heavy Industries, according to company officials.