Tritium Diffusion in A12O3 and BeO

Tritium diffusion in aluminum and beryllium oxides was studied by recoiling tritium into specimens and measuring the time rate of tritium release during postirradiation heating. Results were consistent with classical diffusion solutions and gave single values for the diffusion activation energy over the temperature range of measurement for single-crystal, sintered, and powdered specimens. Varying amounts of tritium were released as tritiated water even after attempts to remove most of the water absorbed by the specimens. Condensable amounts of tritium ranged from <20% for single-crystal specimens to as high as 90% for some powders. Alumina containing 0.2% MgO gave tritium diffusion coefficients 4 to 5 orders of magnitude higher than those for undoped A1₂O₃, implying a significant impurity effect on tritium diffusion. Measured diffusion coefficients were many orders of magnitude lower than hydrogen diffusion coefficients in metals. When a simple equilibrium permeation model was used which neglected tritium partition effects at interfaces and enhanced diffusion along grain boundaries, it was shown that thin coatings of beryllium or aluminum oxides on metal substrates could markedly reduce tritium permeation rates through metals. The present results may be applied in the future to fusion reactors where tritium inventories will be high and tritium diffusion within the blanket region undesirable.