Behaviour of tritium in breeding materials

摘要

The tritium release from ceramic materials of the HCPB under real DEMO operating conditions will depend not only on temperature and neutron flux but also on an intense magnetic field (MF) of 7-9 T. The delay in the tritium release induced by the MF is proportional to the grain size of the ceramics, the squared MF intensity and the abundance ratio of charged tritium forms (T~+, T~-) in the grain volume of the ceramics. The effect of MFs of different intensity on the tritium release from the Li_4SiO_4 pebbles irradiated in the EXOTIC-8 experiment (neutron fluence 2.4 x 10~(25) n m~(-2), irradiation temperature up to 700 K) was investigated in this study. As a result of the irradiation, the grain size of the ceramics increased from 10-15 to 20-40 μm, and the T~+ abundance was up to 86%. The effect of a MF of 2.35 T in these pebbles becomes apparent as a delay in the tritium release by 40% at thermoannealing to 1000 K. The results obtained confirm a hypothesis that MFs lengthen the T~+ diffusion path in the grain volume of the ceramics.