Tritium release and retention in beryllium pebbles irradiated up to 640 appm tritium and 6000 appm helium

Abstract This article covers the investigation of tritium release and retention properties of beryllium pebbles with diameters of 0.5 and 1 mm after neutron irradiation at temperatures of 643-923 K and damage doses of 21-37 dpa corresponding to 3632-5925 appm helium and 367-644 appm tritium productions, respectively. The thermos-desorption spectra have a single main peak for both tritium and helium release. The peak temperatures at both used heating rates of 0.017 K/s and 0.117 K/s are in the range of 1052-1364 K for tritium and 1104-1336 K for helium release. The peak temperatures at a heating rate of 0.017 K/s are always lower than at 0.117 K/s. The tritium retention in both 0.5 and 1 mm beryllium pebbles considerably decreases by increasing irradiation temperature reaching of 1-18 % at the highest temperature of 923 K regardless of the pebble diameter. Open channels are formed in the beryllium pebble microstructure at high irradiation temperatures. These microstructural features contribute to the enhanced release and low retention in beryllium pebbles under neutron irradiation.