Tritium release from breeding blanket materials in high magnetic field

The main problem in fusion reactor technology is fast and complete tritium removal from the tritium breeder and the neutron multiplier - ceramic and Be pebbles. Under the operating conditions, these materials will be at a high temperature (up to 1120 K), under action of intense radiation (up to 1019 n/(m2·s) and magnetic field (MF up to 7-10 T). Up to now, tritium release of these materials was studied only under action of temperature and the neutron radiation of a fission reactor. It is difficult to introduce action of MF in experiments of this kind. A special rig for irradiation of samples at a high temperature up to 1120 K with fast electrons of 5 MeV and dose rate 14 MGy/h in MF up to 1.7 T was used for this study. The activity of the tritium released into a gas phase (molecular tritium T2, HT, HTO) was measured with a gas flow detector. The activity of the tritium remained in the material (the forms of positively charged tritium T+, T2, atomic tritium To and negatively charged tritium T-) was determined by means of both a gas flow detector and a liquid scintillation method after dissolution of the material in acid with scavengers added. A delay of the tritium release in MF of 2.4 T at thermo annealing of the lithium orthosilicate Li4SiO4 pebbles (FZK) irradiated in the EXOTIC-8/8 experiment was observed. Chemical forms of the tritium localised in the pebbles and the tritium distribution were determined (up to 75% - in T+). The delaying effect of MF on the tritium release could be related to lengthening of the diffusion path of T+ in the volume of ceramic grains as a result of the Larmor effect. The beryllium pebbles irradiated in the BERYLLIUM experiment were annealed at 1120 K under the simultaneous action of the radiation and the MF of 1.7 T. The main form of the tritium localised in the Be pebbles is T2 (85%-95%). A stimulating role of MF on the tritium release at the annealing under the radiation was observed (up to 80%). This effect may be related to radiolysis of the localised T2 and the MF-induced spin transformation (singlet-triplet transformation) in the pair of radicals To · To, which increases the concentration of To, which is a better diffusing particle in the grain volume of Be metal. (author)