An ammonia leak that caused an emergency alert at the San Onofre nuclear plant in November was the result of employees failing to recognize degraded equipment and fix it, Nuclear Regulatory Commission (NRC) officials said.
The problem had “very low safety significance,” and faulted plant operator Southern California Edison for failing to follow its own procedures at the twin-reactor site, about 45 miles from San Diego, according to a NRC report on the matter.
The company conducted a parallel investigation and found the same contributing factors as the NRC, according to a company statement. The utility said it made changes to address the findings.
The report came as the company continues to investigate a separate leak in a relatively new steam generator tube that prompted the shut-down of one reactor as a precaution.
The other reactor is off line for maintenance, and inspectors there are continuing to study what the NRC described as unusual wear found in hundreds of similar tubes that carry radioactive water. Watchdog and environmental groups have criticized the utility for not alerting the public for more than an hour after the Nov. 1 ammonia leak started in a storage tank.
The NRC report found workers “failed to adequately identify, evaluate, and correct a problem” in a water purification system, which led to the leak.
No one suffered injury and there was no danger to the public, although some workers ended up evacuated as a precaution. The report said the leak made areas of a building that houses turbines inaccessible.
“The failure to take adequate corrective actions for degraded plant equipment was a performance deficiency. The performance deficiency is more than minor because” it resulted in an emergency alert, the report said.
The report also highlighted confusion among workers.
It found that guidance was not available to operations personnel to fix the tank once they detected a problem. Meanwhile, an equipment operator believed the problem was taken care of when, in fact, it degraded, eventually triggering an alert, the report said.
Exposure to high levels of ammonia can cause irritation, serious burns, lung damage and even death. They use ammonia at the plant to treat water converted into steam, which runs the turbines that produce electricity. The treated water also removes heat from the reactor’s cooling system.
Edison, San Diego Gas and Electric and the city of Riverside jointly own the plant.