OPERATING EXPERIENCE WITH THERMALLY TREATED ALLOY 600 TUBES IN MODEL F STEAM GENERATORS: CRACKING

摘要

Steam generator tube in nuclear power plant is a boundary between primary side and secondary side, whose integrity is one of the most critical factors to nuclear safety. Mill annealed Alloy 600(Alloy 600 MA) tubes which had been used for the first generation steam generators prior 1980 were weak in stress corrosion. To overcome this weakness, thermally treated Alloy 600(Alloy 600 TT) tubes have been introduced to the second generation steam generators after 1980. Alloy 600 TT tubes have performed well in service to date without causing serious problems except some special incidents in the U.S[1, 2]. But, Alloy 600 TT tube crackings have emerged at the hotleg top of tubesheet in some Westinghous F model steam generators in Korea recently, which needs study for the reason and continuous attention. This paper introduces those tube crackings with related data, observes each cracking's characteristics, and looks into their environmental differences, concluding possible causes for them.