By using the two-dimensional rigorous numerical solution of flow and convection-diffusion equations, the H2-HT separative performances of 77 K “cryogenic-wall” thermal diffusion columns with 1,500 mm-fixed height and various radii of 1277 K hot and cold walls with feed rate being parametrically changed. Analyses revealed that the smaller radii columns are useful when feed flow rate is small while larger radii columns are useful when feed rate is large.