IN-situ tritium release experiments from solid breeding materials (TTTEx) — tritium diffusion coefficients and surface reaction on lithium aluminate

In-situ tritium release experiments were performed for γ-LiAlO2 polycrystalline powder (5–9, 6–7, 9–16, 10–14 mesh) and pellets (8 mm diameter × 10 mm high) with three bulk densities of 55% T.D., 78% T.D. and 90% T.D. at 470–780 °C using sweep gas of He+10; 100; 1000; 10000; 30000 ppm H2. The particle size dependence of tritium residence time in the sample was measured using sweep gas of He+10000 ppm H2. The experimental results were analyzed using a two-step diffusion model. Tritium diffusivities in grain (Dg) and for intergrain (Dint) were separately evaluated. The value of Dg was Dg[cm2/s] = 1.82 × 10−7 exp(−84.5[kJ/mol]/RT), and Dint was found to have a strong correlation with the bulk density. The tritium residence time decreased with the increase of H2 concentration in the sweep gas. The major part of the released tritium was the water-forming component in the regime below 1000 ppm H2, while the non-water-forming component was dominant in the regime above 10000 ppm H2.