Unit 2 Steam Generators
Unit 2 commenced a normally scheduled refueling outage on January 10, 2012. This was the first refueling outage after replacement of both steam generators in January 2010. In accordance with the plant's Technical Specifications, a 100-percent inspection of all steam generator tubes was conducted. Mechanical wear was observed at various locations along the tube lengths, similar to what has been observed in comparable steam generators at other plants. The wear observed at the retainer bars was not expected. One tube at the retainer bar had severe wear (90 percent thru-wall). In-situ pressure testing confirmed the structural integrity of this tube.
Based on the severity of tube-to-tube wear found on Unit 3 steam generators, the licensee completed additional rotating coil eddy current testing in an area of interest consisting of 1,375 tubes in each Unit 2 steam generator. Tube-to-tube wear of 14 percent was identified in two adjacent tubes in Unit 2 steam generator 2E089.
Based on the initial 100-percent tube inspections, the licensee completed tube plugging and staking (internal cable support of select plugged tubes) of 192 tubes total: 98 in steam generator 2E088 and 94 in steam generator 2E089. Of the 192 tubes, a total of six tubes, four due to retainer bar wear and two due to anti-vibration bar wear, required plugging because they exceeded the plugging criterion of 35-percent tube wear. Of the remaining 186 tubes, two tubes were preventatively plugged due to anti-vibration bar wear (<35%) and all tubes adjacent to the "retainer bars" were plugged as a precautionary measure due to unusual wear at that location. A total of 323 additional tubes, located in similar areas of tube-to-tube wear in Unit 3 steam generators, were plugged in the Unit 2 steam generators, including two tubes with indications of tube-to-tube wear of 14%. The total plugging for Unit 2 was 207 tubes in steam generator 2E088, and 308 in steam generator 2E089.