Simpler, but still precise, equations of separation that apply to the whole range of concentration for the enrichment of heavy water in a batch-type thermal-diffusion column have been derived by considering the concentration to be of constant pseudoquadratic form. The theoretical predictions compare qualitatively well with the experimental results of previous studies. The present modified equations of separation are easier to use than those obtained in previous studies for optimum design and operation of a batch-type thermal diffusion column for enrichment of heavy water, while the degrees of precision of the present and previous theoretical predictions from the experimental data are almost the same.