A federal commission has submitted its report of San Onofre Nuclear Generators, saying the plants operators acted in accordance with safety procedures during a leak six months ago.
The National Regulatory Commission report was requested after coolant leaked from one of the three units in January of this year. The plant was shut down immediately and hasn’t gone back online since.
Later, inspectors determined that tubes within the Unit 3 steam generator had worn down from excessive friction caused by vibrations.
The report released to the public Thursday details the design flaws that led to the wear. It also inspected operators’ response to the leak in January.
Detection monitors sensed the radiation emitted in the small leak from Unit 3. Although the amount leaked didn’t pose a threat to workers or the public, the operators shut down Unit 3 as a precaution.
“The leak was unexpected,” the report stated, “and the licensee responded in accordance with its procedures by performing a rapid shutdown, since the leak, although small, had increased enough in a short period of time to warrant the precautionary shutdown.”
Testing of the hundreds of tubes showed that some had failed a pressure test, which uses water to simulate the pressure.
Further inspection by the NRC concluded that the curved region of the steam generator was the root of the vibrations – the straw that broke the camel’s back.
The steam created a phenomenon called “fluid elastic instability.” It occurs when steam passes along the tubes at such a high velocity, they vibrate uncontrollably.
This wore several of the tubes down so much, they leaked.
The power plant will remain closed until Southern California Edison workers can figure out how to fix the plant's tubing flaws.
"We are committed to continuing to work with the NRC on the steam generator issues and will continue to use conservative decision making as we work on repairs and planning for the future," said Senior Vice President and Chief Nuclear Officer Pete Dietrich in a statement.
“The number one priority is the safety of the public and our employees.”