High- temperature radiolysis of blanket ceramics

Full text: One of the technological problems of a fusion reactor is changes in the composition and structure of ceramic breeder (Li4SiO4 and Li2TiO3 pebbles) during long-term operation (eg., the operation time of DEMO blanket will be 20000 h). Heavy operating conditions (temperature up to 9000C, the neutron flux up to 1019 n·m-2·s-1, the magnetic field (MF) up to 10 T, etc.) can cause radiolysis of ceramics, grain growth, destruction of ceramic pebbles, etc. The grain growth can cause tritium retention in the grain volume as a result of the Larmor effect. Changes in the composition and structure of the Li4SiO4 (FZK) and Li2TiO3 (CEA) ceramic pebbles at fast electron irradiation (5 MeV, P=100 MGy·h-1, absorbed dose up to 1200 MGy) at 600-10000C were investigated in this study: the changes in composition - by XRD and ESR, in structure - by SEM. The samples were marked with tritium in a photoneutron source (up to 2·1017 n·m-2). Thermoannealing of tritium was performed both at a constant temperature and at a linear temperature increase. No localisation of radiation defects was observed above 6000C in the Li4SiO4 and Li2TiO3 pebbles. The Li4SiO4 grain size increased from 10-15 to 20-25 μm at 9300C and D=1100 MGy. The Li2TiO3 grain size increased from 1-3 to 3-7μm at 9700C and D=1200 MGy. Non-stoichiometric SiO2 increased from 2% to 7%, and Li2SiO3 appeared in Li4SiO4, the melting point decreased. MF effect on the tritium release was not appreciable in all the radiolised samples