EXPERIMENTAL-EVIDENCE FOR TRITIUM RELEASE-CONTROLLING PROCESSES IN LITHIUM SILICATES

Tritium release from lithium ortho- and metasilicate was investigated in in-pile tests and by out-of-pile annealing. Systematic parameter studies and model calculations indicate that for silicates with grain sizes of several ten mu-m and for blanket relevant temperatures (573-873 K) tritium release is mainly controlled by first order reactions at the grain surface. The reaction kinetics above 573 K is sensitive to the surface coverage with oxygen, which depends on the sample pretreatment and the ambient oxygen partial pressure. A strong time dependence in reaction rates was observed, indicating that the release-controlling reactions proceed at changing or energetically heterogeneous surfaces.