The head of the Nuclear Regulatory Commission has said he will visit the San Onofre nuclear plant personally as Southern California Edison grapples with tube wear in relatively new steam generators at both SONGS units.The planned visit by Gregory B. Jaczko, reported Wednesday, follows a confirmatory action letter from the NRC last week that outlined conditions the utility must meet before the Combustion Engineering pressurized water reactors can be placed back in service. Unit 3 was shut down on Jan. 31 after indications of a steam generator tube leak, and subsequent inspections revealed worn tubes in both that plant and unit 2, which was refueling at the time.The NRC reported that Edison has determined the wear was created by tubes vibrating against each other and against support structures within the steam generators, although why that is happening is unclear. In ongoing testing, eight tubes in unit 3 failed under pressures feasible in some accident scenarios.The utility has promised the NRC it will plug tubes showing wear in excess of industry guidelines, as well as tubes vulnerable to wear because of their locations. Edison has been quoted as saying that effort will plug 321 total tubes in both units. It will also determine the root cause of the degradation and establish operational limits and inspections that include mid-cycle shutdowns.The Mitsubishi Heavy Industries-manufactured steam generators were replaced in 2009 and 2010.
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