The HICU PIE results of EU ceramic breeder pebbles: Tritium release properties

Abstract

The former EU reference lithium orthosilicate based breeder pebbles were exposed to neutron irradiation in the HICU (High neutron fluence Irradiation of pebble staCks for fUsion) experiment to test their stability and tritium release properties under DEMO relevant conditions. The samples, varying by three different Li-6 contents, were exposed to irradiation at two different temperatures and the pebbles were either pre-compacted or not. This second part of the post-irradiation examination is focussing on the tritium release behaviour of the ceramic breeder pebbles.The irradiation temperature has the strongest influence on the tritium release behaviour. The tritium inventory is significantly higher for samples that were irradiated at low temperatures. A clear trend regarding higher release rates with increasing Li-6 content was not observed. Tritium is released in a multi-staged process as HTO, HT or corresponding fragments. Fits based on the Wigner-Polanyi equation suggest that recombination reactions of tritium with adsorbed species on the pebble’s surface play the dominant role in the release process. However, the probability for the recombination of two adsorbed T-species on the surface seems to be too low, as no reliable signal for T2 was detected.