The application of H2/HTO isotopic exchange method to the tritium recovery at reprocessing plants was investigated. The size of multiunit exchange column was evaluated numerically for the recovery of tritium from the waste water containing a main impurity, HNO3. The Pt-catalyst packed in the exchange column undergoes weak poisoning by HN03. However, the exchange efficiency of catalyst bed η c is maintained at 0.75 even in the presence of 0.1 mol/l HNO3. As the HNO3 concentration in the waste water is estimated as the order of 10−2 mol/l, the column size is little affected by the HNO3 poisoning. The height and diameter of exchange column required for recovering 99% of tritium generated in a 4 t/d reprocessing plant (recovery efficiency ɛ=0.99) are evaluated as about 6m and 0.63m, respectively. When the tritium concentration in the waste gas is depleted below the environmental protection standard (ɛ=0.9999996), they are evaluated as about 19m and 0.57m, respectively.