Diffusion and trapping of tritium in grainboundaries of 304L stainless steel

Abstract

Permeation rates of tritium through 304L stainless steel are calculated using a grainboundary diffusion model and measured values of bulk and grainboundary diffusion coefficients. Computed results show that the tritium release rate through grainboundaries should be significantly greater than through the lattice. These predictions, however, are not borne out by permeation experiments. In order to explain this discrepancy, autoradiographic examinations were carried out. The results show that although grainboundaries are indeed fast diffusion paths, their contribution to the overall permeation rate may be minimized by trapping in surface oxide films and possibly by low solubility of tritium within the grainboundaries.