By Jim Shilander
Southern California Edison has submitted a response to a letter from the Nuclear Regulatory Commission and is proposing to restart Unit 2 at a lower capacity to verify that repairs made there will be effective.
The proposal, which was sent to the NRC Wednesday, stipulates that if approved, Edison would operate at 70-percent power, which the utility said would prevent the high-speed steam velocity that helped to cause the tube-to-tube wear responsible for the problems at Unit 3. Edison is proposing to operate at that level for five months. It would then shut down the unit for inspection to verify that the structural integrity of the tubes had not been compromised. At 70 percent power, the station would generate 800 megawatts of power.
As to the problems at Unit 3, Edison’s letter to the NRC also states that the investigation found that the cause was fluid elastic instability, caused by the high-steam velocity and low moisture conditions in several locations at the plant, as well as ineffective tube supports. Similar conditions were found in Unit 2, but investigations found that only two tubes were not effectively supported.
On a media conference call to discuss the restart, Edison Chief Nuclear Officer Pete Dietrich said that the investigation found that there had been changes in the manufacturing process at Mitsubishi between the creation of the materials for Unit 2 and Unit 3, which may have contributed to the problems. He emphasized that there had been over 120,000 tube inspections had taken place before submitting the proposal. The company had plugged six tubes in Unit 2, along with preventatively plugging 500 other tubes.
There is no specific date for the restart plan, as it has not yet been approved by the NRC. No specific restart plan has been developed yet for Unit 3, though Dietrich stated that it was possible a restart plan could be put together by next summer at the earliest.