The full scale experimental assembly for study of water distillation and experimental Deprotization Plant are described. The packed sections height of the assembly was 2000 mm. Their inner diameters were from 80 to 150 mm. Characteristics of water distillation columns were studied for three species of random packing. The overall height equivalent to a theoretical plate (HETP) values measured during total reflux mode showed no apparent dependence on vapor flow rate and pressure. The spiral prismatic packing has the HETP value of 26 mm and 43 mm for column of 80 and 150 mm respectively. The ring packing (type Dixon ring) from brass gauze has the smallest pressure drop and the larger operating flow rate of vapor. The Deprotization Plant was built and successfully operates. It allows to remove up to 20 kg H2O per year and upgrade the concentration in heavy water reflector of critical assembly on the level 99.8% D2O. In addition the plant has a possibility for reprocessing of heavy water wastes.