Simulation of helium bubble behavior in neutron-irradiated stainless steel during welding

A simulation model of helium bubble behavior and crack initiation at grain boundaries in the heat-affected zone (HAZ) during welding is proposed, and the effects of welding conditions and helium concentration on bubble evolution and cracking are evaluated. The model was based on the following assumptions; homogeneous bubble nucleation, bubble coalescence by random motion, bubble growth by vacancy absorption and ductile fracture. The result of calculations for different welding heat inputs reveal that the final bubble size increases with increasing the weld heat input and with decreasing bubble spacing at the grain boundary. The calculated critical heat input for cracking as a function of helium concentration is in good agreement with the results of welding experiments on neutron-irradiated stainless steels and helium-doped stainless steels. (orig.)