The Nuclear Regulatory Commission pointed a finger at the design of steam generators manufactured by Mitsubishi Heavy Industries as it summarized recent inspections of premature tube wear at Southern California Edison’s San Onofre nuclear plant.At a public meeting Monday (video below) and in statements by NRC personnel published over the weekend, the federal agency said inspections point to faulty testing and design as likely causes of steam generator problems that have kept SONGS units 2 and 3 offline for months. At the meeting, NRC officials said MHI miscalculated the velocity of water flowing through the steam generators by a factor of three or four, California media reported, leading to unexpected levels of vibration and wear.In an interview with the Associated Press Sunday, NRC Regional Administrator Elmo Collins said inspections have primarily pointed to the steam generators’ design. It was modified to add 400 tubes and V-shaped support structures engineered to minimize tube wear. Instead, eight tubes in unit 3 failed pressure tests, which Collins said was unprecedented in the industry.Both Combustion Engineering reactors have been under inspection since a tube rupture and small steam leak Jan. 31 in unit 3 and the subsequent discovery of premature tube wear in steam generators of both units. The equipment was replaced during outages in 2009 and 2011. While MHI delivered the parts in question, Southern California Edison is responsible for the plant’s license and may face NRC penalties resulting from the inspections. Few indications of a possible restart date emerged during the recent NRC announcements, although Edison executives indicated earlier they do not expect the plant to come back online this summer.
UPDATE: Southern California Edison now says it will file a restart plan with the NRC by the end of July: www.scpr.org/.../restart-plans-san-onofre-be-completed-end-july
Nuclear Street News Team