The effect of purge gas composition on the release of tritium from ceramic breeder materials irradiated in EXOTIC-6

In-situ release experiments: EXtraction Of Tritium In Ceramics (EXOTIC), are performed in the High Flux Reactor, HFR-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. The main objective of this experiment is to determine effect of purge gas composition on release of tritium from various materials supplied by partners in 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 purge gas was varied from 0 to 1% with and without addition of water vapour (25-400Pa). Reduction of the amount of hydrogen in purge gas resulted in a decrease of tritium release rate. Release of tritium was enhanced by addition of water vapour; this was the case for all purge gas compositions, including pure helium. Result of EXOTIC-6 indicated that tritium residence times, determined for reference purge gas, were: lowest for Li2ZrO3 pellets, much longer for Li2ZrO3 pebbles and longest for Li4SiO4 pebbles and LiAlO2 pellets. The residence times of Li6Zr2O7 and Li8ZrO6 are between those of Li2ZrO3 pellets and pebbles. Achieved lithium-burnup was 3%. (author). 3 refs., 5 figs., 2 tabs