(FT/P2-14) Chemical Forms of Tritium in Be Pebbles after Different Treatments

G. Kizane1), J. Tiliks1), A. Vitins1), E. Kolodinska1), V. Tilika1), S. Kaleja1)
 
1) Institute of Chemical Physics of the University of Latvia, Riga, Latvia

Abstract.  Beryllium in a form of pebbles is foreseen as neutron multiplier in the Test Blanket Module for ITER and also in DEMO fusion devices. In order to understand the features of tritium release from the pebbles under operational conditions, it is very important to know chemical forms of localized tritium as they have different mechanisms of diffusion. The paper focuses on the latest results achieved on analysis of chemical forms of tritium in neutron-irradiated beryllium pebbles (EXOTIC 8-3/13 and BERYLLIUM) before and after different conditions of treatment. The pebbles differ by method of production, by irradiation conditions and content of impurities, but they have the same grain size. An annealing of pebbles was performed in the special radiation thermo magnetic rig based on a linear electron accelerator. The chemical forms of tritium were analyzed using a lyomethod. The dissolution of samples was performed in a special system in the presence of only 2 M sulfuric acid and in the presence of 2 M sulfuric acid together with a scavenger of atomic tritium - 0.5 M sodium dichromate. The chemical forms of tritium in pebbles were investigated after they annealing at temperature (490-1023 K) in the presence of ionizing radiation (5 MeV fast electrons, the dose rate 14 MGy/h) and magnetic field (1.7-2.35 T) separately or simultaneously. In both the types of pebbles, the three forms of tritium (ionic, atomic and molecular) were determined. In the untreated EXOTIC 8-3/13 Be pebbles, tritium was in an ionic 10 - 15%, in an atomic 20 - 25% and in a molecular form 60 - 70%. After the treatments at 553K, their abundances had the following values in an ionic form 11 - 25%, atomic 50 - 60% and molecular 30 - 35%. After the treatments at 770K, they had the following values ionic form 10 - 14%, atomic 40 - 45% and molecular 30 - 55%, but after annealing at 1023K only ionic form of tritium was detected. In untreated and treated pebbles of BERYLLIUM, the same chemical forms were determined, but their abundance ratios were different.

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