Hydrogen permeation of Hastelloy XR for high-temperature gas-cooled reactors

Hydrogen permeation of Hastelloy XR, which was developed for high-temperature gas-cooled reactors, has been investigated with a simulated gas to the reactor environment, 80% H₂ + 15% CO + 5% CO₂. In this gas environment, Hastelloy XR formed chromium oxide and manganese-spinel oxide on the surface and showed a good quality to prevent hydrogen permeation. The prevention behavior can be interpreted in terms of a hydrogen diffusion model in a uniform oxide layer, and dependences of permeation rate on time and temperature are explained by variation of oxide thickness. The pressure dependence of the permeation rate for the oxidized alloy as well as bare metals obeyed Sieverts' law. The environmental effects on hydrogen permeation are also discussed on the basis of correlation between the characteristics of the surface layer and the permeation behaviors.