The optimum plate aspect ratios for maximum separation of heavy water, maximum production rate and minimum plate surface area in flat-plate thermal-diffusion column with plate surface area fixed, have been determined. Essential improvement in performance is obtainable if the column is constructed with the best plate aspect ratio, so that the desirable cascading effect can be enhanced, while the undesirable remixing effect can be properly reduced. The maximum separation and maximum production rate are achieved without changing any total expense, while the design with minimum plate surface area results in minimizing the total expense.
