Federal regulators have released a report blaming the November ammonia leak at San Onofre Nuclear Generating Station on employees who failed to recognize or fix degraded equipment.
The Nuclear Regulator Commission took a shot at Southern California Edison because they didn't follow their own procedures at the twin-reactor site about 45 miles north of San Diego and "failed to provide adequate procedural guidance to operations personnel."
The federal evaluation found workers "failed to adequately identify, evaluate and correct a problem" in the water purification system, which in turn led to the leak at the San Clemente plant.
The problem had "very low safety significance," according to the report. Two of the inspection's three "self-revealing" findings were determined to "involve violations of [U.S. Nuclear Regulatory Commission] requirements."
While there was no public health risk and no one was hurt, some workers were evacuated at the time of the leak.
"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, according to the report.
But watchdog groups have criticized SoCal Edison for not alerting the public for more than an hour after the Nov. 1 leak started in a storage tank.
Some workers were evacuated, but there was no public danger.
Meanwhile, the company is investigating a leak in a steam generator tube, as well as unusual wear in hundreds of tubes in the second plant.
SoCal Edison says it has made changes to address the findings.
The report came as the company investigates a separate leak in a relatively new steam generator tube that prompted the precautionary shut-down of one reactor.