Thermal diffusion phenomena of tritium in Nb metal are studied for temperatures between 100°-300°C. Some special types of apparatus and samples are developed to determine the distribution of tritium in the transient state of the thermal diffusion. By least squares fitting of the experimental data to the theoretical curve based on irreversible thermodynamics, the heat of transport, Q*, and the diffusion coefficient, D, of tritium at an average temperature of 200°C are determined to be 18.0 kJ/mol and 1.6 x 10-5 cm2/sec, respectively. The importance of the thermal diffusion phenomena is discussed in connection with tritium permeation through the first wall of a nuclear fusion reactor.
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