The Asahi chemical enrichment pilot plant with four large-scale 1-mm-diam enrichment columns has been operated using the “super” process since June 1987. Uranium with 3.3% enrichment was recovered in April 1988, and higher efficiencies have been observed in the pilot plant than in the bench-scale plant, which has 0.1-mm-diam enrichment columns. A possible reason is that the isotopic backmixing in the pilot plant is much smaller than in the bench-scale plant. Quantitative and statistical studies imply that both the extracolumn volume ratio and wall effect contribute to the smaller backmixing.