The NRC last week began investigating claims by Sen. Barbara Box, D-Calif., and Rep. Edward Markey, D-Mass., that Edison was aware of generator problems linked to the 2012 tube break. The company disputed the account.
The generators, which resemble massive steel fire hydrants, control heat in the reactors and operate something like a car radiator. At San Onofre, each one stands 65 feet high, weighs 1.3 million pounds and has 9,727 U-shaped tubes inside, each three-quarters of an inch in diameter.
Overall, NRC 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.