The Nuclear Regulatory Commission today issued a Confirmatory Action Letter ordering the San Onofre Nuclear Generating Station to remain closed until completion of repairs to the steam generator tubes in both units. According to the NRC’s press release:
“This Confirmatory Action Letter formalizes commitments that Southern California Edison (SCE) has made to ensure that the cause of the tube wear in both steam generators is understood and appropriately addressed in order to ensure safe operation,” NRC Region IV Administrator Elmo E. Collins said. “Until we are satisfied that has been done, the plant will not be permitted to restart.”
The Confirmatory Letter follows initial investigations of excessive steam generator tube wear. According to the NRC press release: “SCE has identified two causes of the unusual wear: tubes are vibrating and rubbing against adjacent tubes and against support structures inside the steam generators. They are still working to determine why this is occurring.”
Southern California will have to complete some specific repairs before the NRC will consider a restart for the reactors:
• SCE will plug all tubes in Units 2 and 3 for which testing indicated wear in excess of industry guidelines, as well as all tubes susceptible to this wear because of their location.
• SCE will determine the causes of the tube-to-tube degradation and establish a protocol of inspections and or operational limits for Unit 2 and 3, including plans for mid-cycle shut down for further inspections. The protocol is intended to minimize the progression of tube wear, and ensure that any tube wear does not progress to the point where it compromises tube integrity.
Here’s a link to the NRC press release and the Confirmatory Action Letter: http://www.nrc.gov/reading-rm/doc-collections/news/2012/12-011.iv.pdf