Mechanical properties of weldments using irradiated stainless steel welded by the laser method for ITER blanket replacement

In the case of a blanket module replacement in the ITER, cooling water pipe will be joined to irradiated pipe by the laser welding method. On the cooling water piping of the ITER blanket, various loads (the vibration of coolant flow, plasma disruption or deadweight of blanket) will be applied to the joint. Therefore, an evaluation of the mechanical properties of weldments using irradiated material is necessary for replacement of the cooling water piping of the ITER blanket. In this study, the bending strength of weldments on irradiated material using the laser welding method was evaluated. This study made clear that the bending strength of weldments using irradiated material with 3.3 appm He by the laser welding method was similar to that of weldments of un-irradiated material to un-irradiated material. On the weldments using irradiated material, small bubbles were observed at the grain boundaries in heat-affected zone because the coagulation of helium generated in irradiated material was accelerated by heat input from laser welding. However, small bubbles did not have a bad influence on the bending strength up to at least 300 °C.