Trouble found during regular inspection of No.3 plant in Mihama Power Station, Kansai Electric Power Co., Inc

No.3 plant in Mihama Power Station, Kansai Electric Power Co., Inc. is a PWR type plant with the rated output of 826 MWe. Its regular inspection has been carried out since September 11, 1989, and eddy current flaw detection inspection was carried out on the total number of steam generator heating tubes (9997 tubes except already plugged tubes). As the result, significant indication was observed in 24 tubes in the expanded parts in tube plates, and in 36 tubes at the boundary of the expanded parts (all on high temperature side), in total in 60 tubes. Consequently, it was decided to plug these 60 defective heating tubes. The heating tubes are those made of Inconel 600, having 22.2 mm outside diameter and 1.27 mm wall thickness. The total number of heating tubes in 10164 (3388 tubes x 3 steam generators), the number of plugged tubes is 227, and the ratio of plugging is 2.2 %. (K.I.)