RESEARCH AND EVALUATION OF LOW TEMPERATURE CRACK PROPAGATION OF Ni BASE ALLOYS IN ACTUAL PLANTS

摘要

Many published results have shown that fracture resistance of Ni base alloys is remarkably reduced by intergranular cracking in low temperature (<150°C) hydrogenated water. This phenomenon is called low temperature crack propagation (LTCP). In order to study maintenance assessment of actual components, J-R tests for Ni base alloys (Alloy 690, 600, Alloy 52, 82 and 152 weld metal) were carried out in simulated PWR primary water to investigate susceptibility to LTCP.J-R tests were performed under the conditions of various temperatures and dissolved hydrogen content. As a result, Alloy 690, 600, Alloy 52 and 82 weld metal showed no significant susceptibility under the conditions evaluated to LTCP. Alloy 152 weld metal showed susceptibility to LTCP in water with dissolved hydrogen content of over 15ccH_2/kgH_2O at 50 °C.On the other hand, as result of investigation on operating condition of actual Japanese PWRs, it was confirmed that there are no possibility of plant operation in 50°C water with dissolved hydrogen content of over 15ccH_2/kgH_2O. Thus, it is evaluated that there is very little possibility that LTCP becomes a threat in actual Japanese PWRs.