TTS crack study in system 80 steam generator

This presentation is to characterize specific degradation that steam generator in Korean standard nuclear power plants has experienced through eddy current testing. Lots of degradation including SCC (Stress Corrosion Cracking) have been reported in CE System 80 steam generator in Korea. Crack occurrence at top of tubesheet (TTS) of steam generator other than wear in square bend area has been paid big attention to SG eddy current industry because it has greatly influenced on tube integrity. It has been reported that the similar steam generators, such as Palo Verde NPP, made previously in the State have experienced not only wear and ODSCC at the upper bundle area but also circumferential ODSCC and PWSCC at TTS. These circumferential SCCs at TTS have initiated in tubing with wide range of microstructure (grain size, carbide distribution), Carbon level, yield strength and annealed temperature. Comparing with the example in the State, it occurred a little earlier. Especially some of steam generators had a problem with fast growth rate