Modeling Of Helium Bubble Formation During Welding Of Irradiated Stainless Steels

Helium atoms are generated in neutron-irradiated stainless steels. In order to predict the post-irradiation weldability, a model is presented to calculate helium bubble formation along grain boundaries during welding of helium containing stainless steels. It calculates helium diffusion toward the grain boundary, bubble nucleation, coalescence and growth at the grain boundary, using the temperature and stress changes during welding. Annealing experiments of helium implanted stainless steels at constant temperatures are analyzed first to examine the bubble formation without tensile stresses. Good agreement with measurements is obtained for the bubble density and the average radius. Then, bubble formations are calculated for a bead-on-tube welding test on a neutron-irradiated stainless steel. Good correlation is confirmed between bubble formation calculations and the crack formation observed in the welding test.