Fig. 9-9 Schematic of test apparatus and structure of blanket irradiation test element Irradiation test element was equipped in the core center of JMTR and tritium, which was produced by neutron irradiation, was taken out of reactor and its characteristics of formation and collection were investigated.

Fig. 9-10 Tritium release behavior to hydrogen flow rate in the sweep gas Tritium release rate decreased when hydrogen flow rate was below 0.2 cm3/min. It is concluded that hydrogen flow rate influences tritium inventory of the Li2TiO3 micro-sphere surface.

One of the roles of the blanket in fusion reactors is to produce tritium by using neutrons, which becomes the fuel of fusion reactors based on D-T reaction. Hitherto, evaluation of tritium breeding characteristics has been performed by in-situ irradiation tests. The tests were not designed to look at tritium release during post irradiation heating, or to be an environmental investigation of the use of a blanket with a small amount of tritium breeding material. We have fabricated irradiation test elements filled by spherical tritium breeding materials (Fig. 9-9) and conducted evaluation of tritium formation and collection characteristics and of nuclear heat characteristics by using the Japan Materials Test Reactor (JMTR). Fine sphere particles made of lithium titanate (Li2TiO3) as a tritium breeding material was chosen because of its good tritium release and chemical properties. Li2TiO3 micro-spheres of 1 mm in diameter and about 140 g in weight (packing density: 62%) were filled up to the irradiation test element. The concentration of tritium which was produced in Li2TiO3 and was sent to a tritium measurement and collection apparatus placed outside the reactor by helium gas containing hydrogen was measured. In the course of reactor operation tritium has been continuously collected and measured by controlling temperature and by flowing helium into micro-sphere packing region. As a result of measurement, we found that tritium release initiated at about 140 degrees cent. Then it was concluded that the collection of tritium would be possible even at lower temperatures (250 - 400 degrees cent.) for designing condition of the International Thermonuclear Experimental Reactor (ITER). As shown in Fig. 9-10, the main parameter which influences the tritium release properties was amount of hydrogen in the packed body. It is considered that the hydrogen flow rate affects the tritium inventory.

Reference H. Kawamura et al., Tritium Release Behavior from Lithium Titanate Pebbles at Low Irradiation Temperature, Proc. of the 20th Symp. on Fusion Technology, Sep. 7-11, 1998, Marseille, France, 1289 (1998).

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