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SAN ONOFRE: Reactor temporarily shut down after backup generators fail to start
By PAUL SISSON – firstname.lastname@example.org | Posted: Monday, December 14, 2009 6:40 pm
Plant operators had to temporarily shut down one of San Onofre Generating Station’s two reactors over the weekend after an emergency generator failed a routine test.
Gil Alexander, a spokesman for Southern California Edison, San Onofre’s majority owner, said Monday that the plant’s Unit 3 reactor was taken off-line at 2 a.m. Saturday when the back-up generators failed to start. A second generator could not be used because it was being repaired.
Generator repairs and testing were completed at around 8 a.m. Saturday and the unit returned to full output, Alexander said.
The incident “posed no risk to public safety,” he said.
Though San Onofre’s nuclear reactors make electricity by heating water and using steam to turn turbines, they still need standard diesel backup generators to provide juice to myriad pumps, valves and other gear that move water through the reactor’s core.
San Onofre usually pulls power off the electrical grid to run that machinery; however, if the plant’s grid connection died, it would need the diesel generators to keep water circulating through the reactor, a process that eventually cools it to a safe temperature.
It was unclear Monday exactly what had caused the back-up generator to fail, but once maintenance was complete on the second, the reactor could be put back into service. A single back-up generator can supply enough power to run the plant in an emergeny, but each reactor at San Onofre has two for redundancy.
It was the maintenance of San Onofre’s backup generators that put Edison under the microscope with Nuclear Regulatory Commission inspectors in August 2008.
An inspection of batteries used to start the generators found that several were connected improperly.
The battery finding led to a special inspection by the commission, which turned up other incidents, including one in which spent nuclear fuel was stored in the wrong location, and brought about several stern public warnings from regulators who said that the plant’s operators have problems spotting and diagnosing minor problems. […cont.]