Based on the operating and fixed charge kept unchanged, considerable improvement in the performance for enrichment of heavy water in a batch-type flat-plate thermal diffusion column is obtainable if operation is carried out by increasing the inclined angle and/or by decreasing the plate spacing. However, decreasing the plate spacing will lead to decreasing the amount of solution to be treated in the column, while increasing the inclined angle will enlarge the operating time for reaching the steady state.