Nuclear Regulatory Commission prohibits San Onofre power plant restart
The U.S. Nuclear Regulatory Commission (NRC) has prohibited Southern California Edison from restarting the San Onofre nuclear power plant, citing serious concerns about equipment failures. You may recall that the plant has been shut down for two months, the longest shutdown in the plant’s history, after a small leak from a tube in the plant’s steam generators released a small amount of radioactive steam.
Neither the regulators nor Southern California Edison estimated when San Onofre, Southern California‘s only nuclear power plan, can be restarted. The plant is a major supplier of electricity for Southern California and produces 2,200 megawatts of electric power, enough electric power for about 1.4 million households.
According to the NRC, tubes in San Onofre Unit 2 were rubbing against the the support structure, but not against each other. In Unit 3, tubes were rubbing against the support structure AND against each other.
The move by the NRC signals that the plant is unsafe to operate. “In Unit 3, a total of eight tubes failed pressure tests in recent weeks. In Unit 2, 192 tubes — about 1% of the unit’s total — showed signs of wear and were taken out of service.”
“Typically, a steam generator can operate at full power with about 8% of its tubes out of service and some have operated with up to 30% out of service, Uselding said.”
The situation posed a threat to safety for two reasons: 1) the rupture of tubes can release radiation, and 2) if many tubes were to rupture at one time, it could compromise the cooling system of the reactor’s core. The situation is surprising because the steam generators are relatively NEW and were manufactured by Mitsubishi Heavy Industries. A spokesman for Mitsubishi, Patrick Boyle said that the tube wear is considered to be “a serious matter” and is supporting Edison in finding the root cause.
Yesterday, an advocacy group, Friends of the Earth, released a report prepared by consultant Arnie Gundersen of Fairewinds Associates, a former nuclear industry executive who is now a critic of the industry. “The report alleges that design changes — including a different alloy used to make the tubes, a change in the flow rate, addition of more tubes and changes in the support structures that hold the tubes in place — probably caused the unexpected wear.”
Under the terms of the NRC letter issued Tuesday, “…before the plant can return to service, Edison must determine what is causing the tubes in Unit 3 to rub against each other and ensure that the same thing does not happen in Unit 2. It also must complete pressure testing of tubes with possibly excessive wear and take those that show too much deterioration out of service, and it must develop a schedule of added inspections once the plant returns to service.
State officials in California are already working on contingency plans to avoid power outages this summer if the plant remains down. Among the options are transmission upgrades, bringing back retired generation units at a natural gas plant in Huntington Beach, and new flex-alerts to encourage customers to use less power, and other conservation efforts.
(Note added April 06, 2012: Today:
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-Bill at
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