Radiation-enhanced exhalation of hydrogen out of stainless steel

Abstract

The state and diffusion of hydrogen in solids have been studied extensively1,2, and the transport of hydrogen and its isotopes in metals has been found to involve classical diffusion and quantum effects such as tunnelling migration and small polaron hopping3,4. The permeability and diffusion of hydrogen isotopes, particularly tritium (T), have been studied in a D–T fusion device5. Diffusion of tritium in the first wall of fusion reactor is expected to occur under high radiation fields due to plasma radiation, self β rays from the held-up tritium and neutron-induced radioactivity6. Heinrich et al. observed α-ray enhanced hydrogen permeation in an iron foil due to activated adsorption of the ionized hydrogen gas on the metal surface7. The γ-ray irradiation from a 1 mCi source, however, caused no appreciable change in permeation in 316 stainless steel5. No detectable loss of tritium was observed from a niobium sample containing 1% tritium8: the effect of the self β rays on tritium diffusion in niobium seems to be negative. We report here an experimental study of radiation-enhanced diffusion of hydrogen in hydrogen-charged stainless steel using direct observation of hydrogen exhalation and lattice dilatation.