Reuters: Financial Services and Real Estate: Workers find issue at San Onofre diesel generators

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Workers find issue at San Onofre diesel generators May 29th 2012, 21:53 HOUSTON | Tue May 29, 2012 5:53pm EDT HOUSTON May 29 (Reuters) - Southern California Edison told U.S. nuclear regulators that its workers identified a potential problem that would have incorrectly shut emergency diesel generators at the San Onofre nuclear station in California at the worst possible time -- when the plant lost off-site power during an earthquake, the company said on Tuesday. An unplanned outage at the 2,150-megawatt San Onofre nuclear plant is about to enter its fifth month as operators deal with the discovery of premature tube wear in the plant's giant steam generators. One or both of the units are expected to be shut this summer, straining the state's ability to meet summer electric demand. In a license event report filed with the Nuclear Regulatory Commission, SCE, a unit of Edison International, said workers discovered that a vibration sensor -- designed to prevent engine damage in the diesel generators from excessive vibration -- could have initiated a shutdown of the back-up power source during an earthquake when the plant lost off-site power. SCE said its engineers continue to analyze the issue and have not concluded whether the sensor would actually cause a shutdown during an earthquake, calling the problem a potential "unanalyzed condition." However, the sensors have been deactivated and "all contingency emergency response actions that ensure the diesel generators operate after an earthquake are still in place," SCE said in a statement. Diesel generators are just part of the back-up safety systems required at all U.S. nuclear plants to supply electricity to emergency equipment in the event of a loss of off-site power that shuts the reactors. Japan's Fukushima nuclear disaster and an East Coast earthquake that shut a Virginia nuclear plant for three months raised concerns from critics and lawmakers about whether the U.S. nuclear fleet could withstand a major earthquake. The NRC has been working with the industry for several years to update the way plants analyze earthquake risk. Also on Tuesday, California Senator Barbara Boxer and Massachusetts Congressman Edward Markey said a Government Accountability Office (GAO) report found that the NRC does not require operating plants to use the most updated method of risk analysis to determine vulnerability to natural disasters, such as earthquakes or flooding. "There is simply no excuse for the NRC's failure to require the most up-to-date methods to assess the threat posed by natural disasters, such as earthquakes, to our nuclear power plants," said Boxer, chairman of the Senate Environment and Public Works Committee, in a statement. The lawmakers said the GAO found that while the NRC has repeatedly recommended the use of a more comprehensive tool called "Probabilistic Risk Assessment," it has not required any operating reactor to actually use the technique to evaluate vulnerabilities to natural hazards. "While the NRC has agreed to study the issue, action is needed now to ensure that standards are in place that best protect the health and safety of the American public," Boxer said. Link this Share this Digg this Email Reprints

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