SCE Commits to Repairs of SONGS Steam Generators

The NRC has issued a Confirmatory Action Letter (attached below) documenting actions that Southern California Edison Co. (SCE) officials have agreed to take related to unusual wear on steam generator tubes prior to restarting both units of the San Onofre Nuclear Generating Station (SONGS).

“This Confirmatory Action Letter formalizes commitments that Southern California Edison 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.”

“We welcome the NRC’s letter, which is a formal step in the process of restarting Units 2 and 3,” said Ron Litzinger, president of SCE, which operates the plant as the majority owner. “Our number one priority is, and always has been, the health and safety of the public and our employees. The utility will only bring the units on line when we and the NRC are satisfied that it is safe to do so.”

On Jan. 31, operators performed a rapid shutdown of the Unit 3 reactor after indications of a steam generator tube leak. Unit 2 has been shut down since Jan. 9 for a planned refueling and maintenance outage. Subsequent inspections at both units have identified unusual wear in many tubes of the steam generators, which were replaced in January 2010 at Unit 2 and January 2011 in Unit 3.

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.

Only one tube required pressure testing on Unit 2. However, six other tubes required plugging, and 186 additional tubes were plugged as a precautionary measure. Eight tubes failed pressure testing at Unit 3, indicating that these tubes could have failed under some accident conditions. Evaluation for additional plugging or other corrective actions are continuing for Unit 2, based on ongoing evaluations of Unit 3 test results.

SCE has committed in writing to the NRC that it “will proceed deliberately and conservatively to implement these steps, always bearing in mind that safety is our first priority.”

SCE has committed to take the following actions prior to restart of each unit:

  • 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.
San Onfre Nuclear Generating Station - NRC SG Letter.pdf

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  • Anonymous

    From David R. Buttemer (retired Calif PE, San Diego,(858)-455-1938): I would be suspicious of an excessive reciculation flow rate (saturated water flow from the steam dryer) due to natural convection (secondary flow rate on outside of tubes is combined FW + recirc flows). This can be easily confirmed if you measure the mixed mean subcooled water temperature entering tube bundle during full power and compare with that for the original SGs.