Deuterium Desorption Behavior of Solid Tritium Breeding Material, Lithium Titanate

摘要

In a solid breeder blanket cooled by water, pellets of Li<,2>TiO<,3> will be employed as tritium breeding material. Structure material in this blanket is low activation ferritic steel, F82H. The operation temperature is limited below approximately 820K owing to swelling caused by neutron irradiation. Tritium produced by fusion neutrons in this breeding material has to be desorbed under a blanket operation for tritium inventory to be small. The blanket module, however, has a spatial distribution of temperature. Thus, the tritium desorption behavior has to be clarified in order to make a scheme for tritium recovery. In the present study, a solid breeding material, Li <,2>TiO<,3>, was irradiated by 1.7keV deuterium ions, and an amount of retained deuterium and deuterium desorption behavior were investigated using a thermal desorption spectroscopy. Dependence of deuterium fluence on amount of retained deuterium was also obtained. In order to examine trapping mechanisms of deuterium in Li<,2>TiO<,3>, similar experiments were conducted for Li and Ti films Deuterium implanted to Li<,2>TiO<,3> desorbed in forms of HD, D<,2>, HDO and D<,2>O. The desorption peak appeared at 500-600K, but significant desorption up to 900K was observed. The range of temperature in the lithium titanate of the blanket module is assumed from 600K to 1200K. These results suggest that the tritium produced in the blanket is partly not desorbed. Thus, the spatial distribution of temperature in the blanket has to be controlled for the tritium to be desorbed during the operation. The desorption spectra of deuterium in Li<,2>TiO<,3> were similar to those of Li. This suggests that most of implanted deuterium is trapped in forms of Li-D and Li-OD. Based upon the present results, a tritium inventory and a suitable design for the blanket module are discussed.