Localization of Radioactive Steam after the Safety Valves in a Water-Moderated and -Cooled Reactor

Abstract

The radiation and explosion safety of water-moderated and -cooled reactors in regimes with steam discharged through safety valves is described. It shown for the VK-50 boiling-water reactor that diverting the steam after the safety valves to outside the protective shell minimizes the consequences of emergencies during planned hydrogen discharges into the atmosphere and guarantees localization of the radionuclides.The concept of radiation safety for water-moderated and -cooled reactors in NPPs of different types consists of maintaining reliable barriers in the propagation path of radioactive substances. If the safety valves are actuated, the coolant flows into the protective shell, where the radioactive isotopes continue to decay. Discharging the coolant through the safety valves of a water-moderated and -cooled reactor during a steam-zirconium reaction can lead to the formation of an explosive concentration of hydrogen inside the protective shell. Passive catalytic hydrogen recombiners do not utilize explosive gas in a moist steam-gas mixture. If an explosive mixture forms, the protective shell could be destroyed.A system for localizing steam after the safety valves and for diverting the medium being discharged to outside the protective shell has been built and tested in a VK-50 boiling-water, research, vessel reactor. This system was developed on the basis of studies of the combustion of radiolytic hydrogen. It utilizes radioactive gases even if leaky fuel elements are present in the core. Experience in operating this system in VK-50 showed the technical and technological solutions forming the basis for its development are correct.System for Localizing Steam after the Safety Valves. The VK-50 reactor facility is the prototype for a power-generating unit developed to study the serviceability, reliability, safety and cost-effectiveness of vessel-type boiling-water reactors with all-regime natural circulation of the coolant and steam output from the reactor to a turbine [1]. Safety systems based on passive gravitational principles and radiation and explosion safety during coolant boiling in the core [2], including a system for discharging steam through safety valves into the atmosphere, were developed, tested and improved on the VK-50 reactor. Discharging the steam-gas mixture to outside the facility should eliminate the formation of an explosive hydrogen concentration in the reactor and pipelines after the safety valves.The activity of the emissions into the environment is reduced by using an interphase (water-steam) barrier that is weakly permeable to radioactive products of corrosion propagating to the outside of the reactor [3]. Gamma-emitting products of corrosion 59 Fe, 60 Co, 65 Zn, 51 Cr, and 54 Mn are carried off together with moisture. The low level of radioactivity in steam is due to the fact that the products of corrosion are predominately found in the form of suspended particles, which are removed only with drops. The specific activity of radioactive products of corrosion in steam is almost 100 times lo...