PNNL

Abstract

As an experimental basis for helium induced weld cracking of neutron irradiated austenitic stainless steels, helium diffusivity has been evaluated by measuring helium release rates at high temperature. Isochronal and isothermal experiment were performed at temperatures between 700 and 1300 ? for Type 304 and 316L stainless steels. In 1 hour isochronal experiments, helium was released beginning at ~900? and reaching near 100% at 1300 ?. No apparent differences in helium release rate were observed between Type 304 and 316L stainless steels. At temperatures between 1100 and 1300 ?, the diffusion rate was calculated from the time dependence of the helium release rate to be: D0=3.42×104 cm2/s, E=173.2 kJ/mol. The observed activation energy suggests that the release of helium from the steels is associated with the removal of helium from helium bubbles.