THE EFFECT OF PURGE GAS COMPOSITION ON THE RELEASE OF TRITIUM FROM CERAMIC BREEDER MATERIALS IRRADIATED IN EXOTIC-6

Abstract

In-situ tritium release experiments, codename EXOTIC (EXtraction Of Tritium In Ceramics), are performed in the High Flux Reactor (HFR) at Petten and aimed to determine tritium residence times for various ceramic breeder materials at different temperatures, purge gas compositions and irradiation times. EXOTIC-6 is the second medium term irradiation of this series and lasted about 200 FPD. In this experiment the main objective is to determine the effect of purge gas composition on the release of tritium from various materials supplied by the partners in the European Blanket Technology programme: KfK Karlsruhe (Li4SiO4 and Li2ZrO3 pebbles), ENEA Casaccia (LiAlO2 and Li2ZrO3 pellets), CEA Saclay (LiAlO2 and Li2ZrO3 pellets) and ECN Petten (Li6Zr2O7 and Li8ZrO6 pellets). The reference purge gas was He + 0.1 vol.% H2. The H2 content in the purge gas was varied from 0 to 1 % with and without addition of water vapour (25–400 Pa). Reduction of the amount of hydrogen in the purge gas resulted in a decrease of the tritium release rate. The release of tritium was enhanced by addition of water vapour; this was the case for all purge gas compositions, including pure helium. The results of EXOTIC-6 indicated that the tritium residence times, determined for the reference purge gas, were: lowest for the Li2ZrO3 pellets, much longer for the Li2ZrO3 pebbles and longest for the Li4SiO4 pebbles and the LiAlO2 pellets. The residence times of Li6Zr2O7 and Li8ZrO6 are between those of Li2ZrO3 pellets and pebbles. The achieved lithium-burnup was 3%.