Heavy water is used as a neutron moderator and coolant in nuclear power and research reactors. During operation of heavy water reactors, heavy water becomes contaminated with tritium and protium. Protium comes from various sources, such as a result of isotope exchange from constructional materials and sorbents, from the atmosphere as water vapor, and from the faulty equipment in the form of water. Tritium is produced in heavy water owing to neutron capture by deuterium atoms. Thus, heavy water reactors require facilities to keep deuterium concentrations within operating margins and remove tritium. A schematic diagram of a detritiation plant has been developed to maintain the characteristics of heavy water in the reflector of reactor. The plant is designed to address the problems related to management of heavy water at the reactor site. Protium recovery capacity of the plant is not a fixed value. It can vary widely depending on the actual leakage of light water in a heavy water reactor loop. The initial data for modeling were obtained in the course of long-term operation of EVIO pilot plant. The evaluation of the basic parameters of the installation has been done using computer models.