THE EFFECT OF TEMPERATURE ON THE CRACK GROWTH RATE OF STAINLESS STEEL AND NI-ALLOYS IN SIMULATED BWR ENVIRONMENT

摘要

The effect of temperature on the crack growth rate (CGR) in BWR normal water chemistry (NWC) has been investigated in various studies over the years. However, the effect has not been clarified unambiguously, since some studies report a maximum in CGR at a temperature of about 200 °C, while others have reported a monotonic increase of CGR with temperature. To clarify the effect of temperature, testing has been performed in oxygenated high-purity water (NWC with 500 ppb O_2 and conductivity ranging from 0.1 to 0.2 μS/cm). Crack growth rate measurements were conducted on six 25 mm compact tension (CT) specimens in simulated NWC environment at ~30 MPa√m. Two heats of sensitized stainless steel and one heat of alloy 182 were tested, and the temperature ranged from 288 to 100 °C. Intergranular or interdendritic cracking was observed in all specimens. The DCPD response clearly showed that the crack growth rate in stainless steel increased monotonically with increasing temperature. Alloy 182 showed no temperature dependence in this work. A possible reason for the different conclusions in the literature was identified. For short testing times on each temperature (about 50 h) a maximum in CGR at -200 °C was observed, while a monotonic increase was observed if longer durations were considered.