- SCE determined the tube-to-tube wear in the Unit 3 steam generators was caused by a phenomenon called fluid elastic instability, a combination of high-steam velocity and low-moisture conditions in specific locations of the tube bundles and ineffective tube supports in the same locations.
- The high-steam velocity and low-moisture conditions existed in Unit 2 and hence Unit 2 was susceptible to the same vibration-causing environment. However, of the almost 20,000 tubes in Unit 2, all except two are known to have been effectively supported throughout its 21-month operating period.
- SCE will operate Unit 2 at 70 percent power, which will prevent the vibration-causing environment by decreasing steam velocity and increasing moisture content. The 70 percent power level will result in steam velocities and moisture content consistent with those that the industry has successfully operated under for many years.
- SCE has chosen a conservative operating period of five months. SCE will shut down Unit 2 after five months for inspection of the steam generator tubes to ensure the continued structural integrity of the tubes, to measure tube wear and to confirm that the solutions are working. The five-month operating period affords an additional safety margin beyond the analysis provided by the independent experts.
- SCE has plugged six tubes in Unit 2 indicating wear with greater than 35 percent through wall depth and preventively plugged more than 500 other tubes. Steam generators are built with an allowance of extra tubes so that tubes may be taken out of service for a variety of reasons, including wear, and only 2.6 percent of the total tubes in Unit 2 have been plugged.
Southern California Edison Submits Response To Confirmatory Action Letter And Unit 2 Restart Plans To Nuclear Regulatory Commission
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