Southern California Edison said Friday that refueling operations at San Onofre Nuclear Generating Station’s Unit 2 reactor are complete after nearly half of the reactor fuel was replaced with new fuel. The nuclear plant is still forced to delay restarting a reactor that showed accelerated wear on its generator tubes in order to perform more intensive analysis.
The utility shut its Unit 3 reactor down on Jan. 31 after detecting a leak in one of two large heat exchangers that are critical in generating steam that allows the plant to generate enough electricity. ”Until the inspections and tests are completed and the data analyzed, it would be premature to comment on the return of Unit 3 to service,” Utility spokeswoman Jennifer Manfre said.
Subsequent inspections forced workers to plug and decommission over a thousand tubes inside of the San Onofre heat exchangers. When the tube problems in Unit 2 were discovered, a spokesman for the U.S. Nuclear Regulatory Commission said hundreds of tubes appeared to show wear and thinning. A first round of tests by the plant operator confirmed concerns about accelerated wear on over 1 in 20 of the nearly 20,000 tubes within two generators at reactor 2, over 850 of them thinning by 10% in a little over 2 years, and no definitive numbers have been released for the other two generators at reactor 3.
According to the Nuclear Regulatory Commission’s finding that a minimum 871 of 19,400 tubes have thinned by 10 percent or more, a total of 4.5 percent of the tubes have been compromised to some extent, almost one in twenty. Up to 7 percent of generator tubes can be taken out of service before performance is affected appreciably.
Edison spokesman Alexander said the plant’s steam generators were built with an allowance of extra tubes.