Chemical interactions in the EXOTIC-7 experiment

Post-irradiation studies by X-ray microanalysis are reported on selected samples of the MANET steel lined capsule 28.2 of the EXOTIC-7 experiment within the fusion breeder blanket materials irradiation programme. A mixture of Be pebbles and SiO2 doped Li4SiO4 pebbles with 52% 6Li enrichment has been irradiated in the HFR up to 18% burn-up. A Li/Si decrease in the breeder material is observed due to Li transmutation which results in higher amounts of Li2SiO3 in the Li4SiO4 pebbles. Furthermore, oxygen is released which oxidises the surface of the Be pebbles to BeO. Direct BeO-Li2SiO3 contact leads to the formation of Li2BeSiO4. The predominant Li2O vapour species is transported to the colder, inner liner surface of the pebble bed and recondenses as stratified Li2O and Li8SiO6 layers. The chemical reactions between the MANET steel liner and the breeder materials play a minor role. (orig.)