Electrolytic reactor that converts methane and water simultaneously to liberate hydrogen isotopes at very high conversion ratio was developed and tested. Addition of the second zirconia cell provides the capability of processing broad mixing ratio between water and methane by supplying or extracting oxygen. Combination of palladium permeation and electrolytic reactions was tested under reactor relevant tritium concentration in an integrated loop. Satisfactory processing of simulated plasma exhaust processing and tritium recovery was verified. Based on the result, a concept of the fuel processing system for fusion reactor is proposed and discussed.