Status of lithium oxide blanket material research

Preparation of Li²O pellets has been accomplished by the press-sintering method, using Li²O powder which was produced by thermal decomposition of Li²CO³ as a starting material. The reaction between Li²O and moisture-containing air was preliminarily studied on the view of handling pellets. Li²O has relatively high thermal conductivity compared with other solid blanket candidates. Its thermal expansion coefficient was also measured. Thermodynamical properties on solubility and diffusivity of hydrogen in Li²O pellet were measured by an equilibrium-quenching and hot-extraction method. Dissolved amount of hydrogen was 2 to 4 wppm at 10₅ Pa of hydrogen pressure in the temperature range 770 to 970 K. On the other hand, the amount of hydrogen existing in Li²O as an atomic state was extremely little according to an electron spin resonance measurement. For the compatibility of Li²O with container materials, the incipient reactions with Cr, Fe and Ni were studied by ₄He-backscattering method. In addition, the reactions of Li²O with commercial alloys were examined and a comparative evaluation was deduced. Tritium produced in Li²O by the ₆Li(n,α)T reaction was released mostly in the form of HTO(g) through heat treatment (473-870 K) under vacuum. The diffusion coefficients were determined for Li²O powders and pellets in different neutron fluences (10₁₅ to 10₁₇ n/cm₂). The rate-determining step of HTO(g) release from Li²O was found to be diffusion of tritium in the solid. In-pile tests of tritium release from Li²O pellets are planned in thermal neutron fluences (10₁₈ to 10₂₀ n/cm₂) at present. (author).