The owners of the San Onofre nuclear power plant have agreed to pay a $180,000 fine for violations of federal regulations that led to a serious accident in one of the plant's reactors last year.
David Barron, a spokesman for Southern California Edison Co., said the company has accepted responsibility for the Nov. 21 accident, which kept reactor Unit 1 shut down for more than eight months.
"Edison has chosen not to contest it since the event did happen, did involve a potential safety matter and has resulted in Edison and the Nuclear Regulatory Commission taking a number of steps to prevent this from happening again in the future," Barron said.
The fine is the highest ever paid by Edison for an accident at San Onofre.
The three violations involved the breakdown of a key feedwater system that helps cool the reactor, the failure of the utility's test program to ensure that the system's valves would work, and the failure of Edison workers to fully investigate a problem they discovered in one of the valves.
The NRC said the violations led to the accident, in which the failure of five valves combined with the effects of a 4-minute power outage to cause what is known as a "water hammer"--the over-pressurization of a 10-inch pipe and a resultant shock wave that cracked the pipe, damaged several pipe supports and released non-radioactive steam into the atmosphere.
The incident ended with no injuries, no release of radioactivity and no danger to the public.
An NRC report on the incident earlier this year concluded that maintenance records for the valves that failed were either missing or lacked specificity, that testing records were inconsistent and that the testing procedure used on the valves "was not rigorous."
The key failure by Edison was a decision to postpone visual inspection of a valve first detected making a "loud rapping or metal tapping noise" in June, 1985. After an investigation, plant workers decided to inspect the valve during the plant's next shutdown. But by the time of the next outage in August, the noises in the pipe had disappeared, and "no additional attention was paid to the valve," according to the report.
In fact, the noises stopped because the valve fell apart and stopped working.
Not knowing if the valve had broken or not, plant supervisors decided that, even if the valve had failed, the reactor could be operated safely because four other valves would have to fail before a serious problem developed.
But on Nov. 21, at the end of a 4-minute power outage, all five valves failed, emptying water from three 10-inch pipes and partially filling those pipes with steam. When cold water was then brought into those lines, the water condensed the steam and created an area of low pressure. This "water slug" then moved rapidly and with great force from areas of higher to lower pressure until it hit an elbow in the pipe. The force of that blow is known as a "water hammer."
"They never dreamed you'd have five of those valves fail at the same time," said Al Johnson, enforcement officer for the NRC's Western region office in Walnut Creek. "To be quite frank, most people wouldn't think you'd have something like that go wrong with all of your check valves."
Edison was fined $80,000 for the event, which was classified as a level two violation, the second most serious on the NRC's scale of one to five. The utility was fined $50,000 for failing to maintain an adequate testing program and $50,000 for failing to inspect the faulty valve after it was discovered. Those two violations were classified as level three.
Since the accident, Edison has redesigned the faulty valves and added three more to the system in an attempt to ensure that all do not fail simultaneously again.