Tritium release behavior from liquid tritium breeding materials for fusion reactor blanket under neutron irradiation

In-situ tritium release experiments on Li17-Pb83 molten alloy and LiF-BeF(2) molten salt were carried out using the fast neutron source reactor "YAYOI" of the University of Tokyo. Regarding Li17-Pb83, chemical form of released tritium was mainly HT or T(2). The diffusion coefficient in molten Li17-Pb83, the mass-transfer coefficient from Li17-Pb83 to purge gas, and the overall mass-transfer coefficient of tritium permeating through structural materials such as iron and SUS 304 were obtained. Stable oxide layer including Cr(2)O(3) and FeCr(2)O(4) formed on the surface reduced the mass-transfer coefficient. In particular, a kind of ceramic coating was quite effective as a tritium permeation barrier. Regarding LiF-BeF(2), on the other hand, chemical forms of released tritium from Flibe are HT and TF, depending on H(2) and F(-) activity in the system. In case of low H(2) activity and high F(-) activity, TF was dominant. Three tritium transfer processes were considered: direct release of T(+) to purge gas as TF (process (1)), conversion from T(+) to HT (process (2)), and release of HT to purge gas (process (3)). Among them process (3) is much faster than process (1). The reaction rate of process (2) is so much influenced by H(2) and F(-) activities in the system that each process could be the rate-determining process depending on H(2) and F(-) activities. When process (3) was the rate-determining process, the overall mass transfer coefficient was estimated. (C)1997 Elsevier Science Ltd.