Measurement of the growth kinetics of cracks in bainitic NPP pressure vessel steel under stress corrosion cracking conditions

To evaluate the possibility of stable crack growth in the reactor pressure vessel wall due to the stress corrosion cracking (SCC) mechanism and as well as to calculate the life time of the pressure vessel, the kinetics of the crack growth should be evaluated. The paper deals with the comparison between the behaviour of small and large cracks from the point of view of SCC. The material 15Kh2NMFAA used for the WWER-type RPVs, as the base material, was chosen for the experiments. Slow strain rate tests are carried out on tensile specimens to evaluate the kinetics of small environmentally -initiated cracks. The slow displacement rate are applied to CT specimens is used to evaluate the kinetics of large pre-existing cracks. To compare the response to different water chemistry conditions, tests have been carried out in WWER primary circuit environment with low (below 20 ppb) and high (higher that 1 ppm) dissolved oxygen (DO) content. All the tests have been done in through-flow autoclave system with controlled water chemistry. (author)