Electrolytic method for concentrating heavy water

PROBLEM TO BE SOLVED: To provide a method for the electrolytic concentration of heavy water that enables raw water containing a large amount of heavy water to be electrolytically concentrated by a method for alkali water electrolysis, fractionated, and high-purity gas or/or oxygen gas to be produced.SOLUTION: An electrolytic solution 16 obtained by adding high-concentration alkali water 7 to raw water 10 composed of heavy water containing tritium is circularly supplied into both electrolysis chambers of an anode chamber 2 and a cathode chamber 3 from a circulation tank 5 that stores the electrolytic solution. An anode side gas liquid separation device 14a and an anode side water sealing device 15a and a cathode side liquid separation device 14b and a cathode side water sealing device 15b are connected to the anode chamber and the cathode chamber, respectively. The electrolytic solution from which a generated gas is separated by the anode side gas liquid separation device and the cathode side liquid separation device is circularly supplied into the circulation tank, thereby continuing the electrolysis while the alkali concentration of an electrolytic solution to be supplied into both the electrolysis chambers is always maintained at a constant concentration to concentrate the heavy water in the electrolytic solution, and to recover or discard the hydrogen gas or the oxygen gas.