Measurements were made of T diffusion in the stainless steels, at temperatures ranging from 25 to 222C, by directly monitoring T diffusion gradients. The Li6(n,α)3H reaction was used to inject T into the specimens and to produce initial T concentrations ranging from 0.0005 to 0.007ppm[wt] of 3H by weight. Three components were identified in the concentration profiles: these were a surface region that was approximately 5μ thick and where T-trapping occurred, a normal diffusion profile which was characteristic of bulk diffusion, and a rapid-diffusion tail which was tentatively attributed to grain-boundary diffusion. Surface release measurements of T verified the existence of a surface trapping-layer. The bulk diffusion component was consistent with classical diffusion solutions and furnished essentially the same data for both steels:

D (cm2/s) = 0.018 exp[-0.61(eV)/kT]

The surface trapping was tentatively attributed to the presence of He-stabilized voids in the surface layers.

Tritium Diffusion in 304- and 316-Stainless Steels in the Temperature Range 25 to 222°C. J.H.Austin, T.S.Elleman: Journal of Nuclear Materials, 1972, 43[2], 119-25

Table 62

Bulk Diffusion Parameters for AISI 304 Stainless Steel

Figure 9

Permeation of H in AISI 302

(open squares: H2 ambient, filled squares: H2/H2O ambient)