Equilibrium concentration and diffusion controlled leaching model for cement-based waste forms

A predictive model for nuclide leaching from cementitious waste form is developed based on diffusion, the sorption equilibrium concept in the waste form, and continuity boundary conditions of concentration and concentration gradient on the waste form surface. A concept to determine the equilibrium concentrations of radionuclides in pore water of the waste form is presented. Nuclide release unrelated to diffusive transport mechanism is reflected on the model as a wash-off fraction which depends on the surface conditions of the waste form. The double region model proposed in this paper gives much lower nuclide release rates than the single region model. This leaching model is calibrated by comparison with the results of a leaching experiment performed at JAERI.