Development of measurement technology of chlorine attached on canister using laser. Effect of pulsed-laser irradiation on initiation of stress corrosion cracking

In order to evaluate the effect of pulsed-laser irradiation on initiation of stress corrosion cracking (SCC), atmospheric stress corrosion cracking was examined for candidate canister material used for concrete cask. Residual stress was also measured to clarify the initiation of SCC induced by laser irradiation. A stainless-steel (UNS S30403) irradiated by second harmonic of Nd:YAG laser pulses (pulse width:10ns, wavelength:532nm) was used as a specimen for the corrosion test and the stress measurement. When the laser energy was 30mJ, the SCC was observed after exposure to the test environment at the point of laser irradiation. Most of the cracks have a length of less than 40 μm; and its averaged value was not changed between the test duration of 1500h and 3000h. The tensile residual stress was about 300 MPa at the surface of the specimen and decreased with the depth from the surface. The residual stress at the irradiated and unirradiated points were same at the depth of 45 μm which corresponds to the crack length observed at the specimen. The results show that the effect of pulsed-laser irradiation on the initiation of SCC can be explained by the tensile residual stress induced by laser pulses. (author)