Fig. 9-3 The sintered Li2O pellet irradiated with neutrons, and optical micrograph of a radial cross section

Fig. 9-4 Cross sectional microstrucure in neutron irradiated Li2O ceramic specimen

Sintered lithium oxide (Li2O) pellets were irradiated with neutrons in the Fast Flux Test Facility, and a radial cross section of the irradiated specimen was examined with an optical microscope (Fig. 9-3); 4-5 % of Li in the ceramic specimen was transmuted to T and also He by the neutron irradiation. Although extensive microstructural change and resultant swelling occurred during the irradiation, no serious problem of the integrity of the specimen was observed. Thus, the Li2O ceramic is expected to meet the design specification for solid tritium breeding material in a fusion experimental reactor. Columnar grains formed along the temperature gradient are seen in Fig. 9-4, together with a center void at the high temperature end. Lenticular pores formed along the boundary of the columnar grain were not observed to be a precursor of cracking in the ceramic specimen. Furthermore, neither serious damage nor significant interaction with cladding materials have been observed in the Li2O ceramic after neutron irradiation. In addition, the recovery of tritium generated in the Li2O specimen has been demonstrated in in-situ tritium release experiments in the JRR-2 reactor.

Reference T.Takahashi, et al., Changes in the Microstructure and Density of Li2O during Irradiation in BEATRIX-II. Phase I, Fusion Eng. Des., 28, 271 (1995).

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