Patent Number: 
Section: claims

1. A method for treating tritium water-containing raw water by which tritium water-containing raw water is treated by a first alkali water electrolysis step comprising the steps of:(1) supplying a part of raw water containing tritium water and alkali water to a circulation tank;(2) mixing the raw water with the alkali water in the circulation tank to obtain an electrolyte adjusted so as to have a desired alkali concentration, supplying the electrolyte to an alkali water electrolysis device, and performing electrolysis treatment;(3) supplying the raw water continuously to the circulation tank in an amount which corresponds to raw water lost by the above electrolysis treatment to maintain alkali concentration at an adjusted initial concentration, and continuing the electrolysis treatment while circulating the electrolyte in order to continuously perform the alkali water electrolysis treatment;(4) gasifying the raw water to tritium-containing hydrogen gas and oxygen gas so that tritium concentration is diluted to 1/1,244 relative to tritium concentration in the raw water; and(5) reducing the volume of the raw water. 2. The method for treating tritium water-containing raw water according to claim 1, wherein the tritium-containing hydrogen gas generated by the first alkali water electrolysis step is taken out to open air. 3. The method for treating tritium water-containing raw water according to claim 1, wherein the tritium-containing hydrogen gas generated by the first alkali water electrolysis step is sent to a catalyst tower, the tritium-containing hydrogen gas is reacted with water vapor on a catalyst filled in the catalyst tower, and the tritium is recovered as concentrated tritium water-containing water. 4. The method for treating tritium water-containing raw water according to claim 1, the method comprising:the first alkali water electrolysis step for performing continuously the alkali water electrolysis treatment;a second distillation step in which, after completion of the first alkali water electrolysis step, the entire amount of the electrolyte remained in the first alkali water electrolysis step is supplied to an evaporator, an alkali component in the electrolyte is recovered as alkali salt slurry, and simultaneously, tritium water-containing water distilled by the evaporator is taken out; anda second alkali water electrolysis step in which the tritium water-containing water taken out by the second distillation step and new alkali water are supplied to a circulation tank, the tritium water-containing water is mixed with the new alkali water in the circulation tank so as to have an electrolyte solution with a desired alkali concentration, electrolysis capacity of an alkali water electrolysis device is adjusted to the capacity suitable for a treatment amount of the electrolyte, an alkali water electrolysis treatment is performed followed by batch treatment, the tritium water-containing water is gasified and converted to tritium-containing hydrogen gas and oxygen gas so that tritium concentration is diluted to 1/1,244 relative to tritium concentration in the tritium water-containing water, and the volume of the raw water is reduced,if necessary, further comprising a step of repeating several times the second distillation step and the second alkali water electrolysis step until the completion of the batch treatment in which, at the time of repeating several times, the capacity of the alkali water electrolysis device used for the second alkali water electrolysis step is gradually reduced and the treatment is repeated. 5. The method for treating tritium water-containing raw water according to claim 1, wherein, when raw water which contains impurities including a large amount of chloride ions is used as the tritium water-containing raw water, a first distillation step for removing the impurities is further provided as a pre-step of the first alkali water electrolysis step, and in the first distillation step, the raw water which contains impurities including the chloride ions is supplied to the evaporator and the impurities are removed as salt slurry, and simultaneously, the tritium water-containing raw water after removing the impurities is taken out and then continuously supplied to be treated by the first alkali water electrolysis step. 6. The method for treating tritium water-containing raw water according to claim 4, wherein, when raw water which contains impurities including a large amount of chloride ions is used as the tritium water-containing raw water, a first distillation step for removing the impurities is provided as a pre-step of the first alkali water electrolysis step, and in the first distillation step, the raw water which contains impurities including the chloride ions is supplied to the evaporator and the impurities are removed as salt slurry, and simultaneously, the tritium water-containing raw water after removing the impurities is taken out and then continuously supplied to be treated by the first alkali water electrolysis step. 7. The method for treating tritium water-containing raw water according to claim 5, wherein, in the first distillation step, the salt slurry is concentrated and then separated and recovered as a solid matter. 8. The method for treating tritium water-containing raw water according to claim 4, wherein, in the second distillation step, the alkali salt slurry is concentrated and then separated and recovered as a solid matter. 9. The method for treating tritium water-containing raw water according to claim 4, wherein, in the first alkali water electrolysis step, alkali water with relatively high concentration is used as the alkali water and the electrolysis treatment is performed at relatively high current density, and in the second alkali water electrolysis step, alkali water with relatively low concentration is used as the alkali water and the electrolysis treatment is performed at relatively low current density. 10. The method for treating tritium water-containing raw water according to claim 1, wherein, in the first alkali water electrolysis step, 15% by mass or more of alkali water is used as the alkali water, and the electrolysis treatment is performed at current density of 15 A/dm2 or higher. 11. The method for treating tritium water-containing raw water according to claim 4, wherein, in the second alkali water electrolysis step, 2 to 10% by mass of alkali water is used as the alkali water, and the electrolysis treatment is performed at current density of 5 to 20 A/dm2.