Although the method of adsorption using synthetic zeolites has been applied to the systems of removal or/and recovery of tritiated water vapor from tritium handling atmospheres or process gases, the dynamic behavior of hydrogen-isotopic water molecules in zeolites is not yet sufficiently elucidated because the interaction between strongly polarized water molecules and zeolite crystalline surfaces is complicated. Considering the basic definition of mass transfer with the chemical potential gradient as driving force for diffusion, we obtained an expression of diffusivity depending on temperature and concentration, derived from the characteristics of adsorption equilibrium as a function of adsorption potential, where the diffusivity is described in relation to the mobility corrected here by deriving a term of activation energy.

Experimental diffusion coefficients for tracer HTO in H2O adsorbed in zeolite crystals, measured under various conditions of temperature and vapor pressure, indicate a variety of values. The variety, however, can be clearly interpreted in accordance with this expression.