The deuterium release behaviour in gamma ray-irradiated candidate breeder ceramics

The work summarizes the obtained results on deuterium absorption and thermal induced desorption experiments performed on ceramic breeder candidate compositions. To simulate tritium (T) residence time (or T diffusion) in a DEMO-like ionizing environment, gas sorption­ desorption experiments of deuterium (another H isotope) during ionizing radiation in breeder ceramics were proposed as an alternative method to validate the functional properties of tritium breeder materials in the Helium Cooled Pebble Bed (HCPB) breeder-blanket concept. Pellet- and pebble-shaped samples of lithium orthosilicate and lithium metatitanate compositions were exposed to 1 mbar D2 atmosphere while being irradiated up to 4 MGy gamma-ray ionizing radiation. Then, the D2 desorbed rate signal was followed by mass spectroscopy as a function of temperature up to 800 "C and a temperature rate of 10 K/min for pebbles and pellets samples. From the experimental desorption curves and the calculated activation energies, discussion on the involved D2 trapping centres were obtained. D2 seems to be trapped in defects common to lithium orthosilicate and metatitanate crystalline structures. ... mehrThe trapped D2 is observed to be released below 300 "C due to a low activation energy process, but also at temperatures above 600 •c. Ionizing radiation up to 4 MGy modifies the electronic structure of defects affecting the
sorption and desorption processes. Concerning fusion applications, the obtained results led to conclude that the tritium produced at least in lithium orthosilicate based breeder ceramics would be effective at operational temperature and radiation conditions.