Calculation of the Impact of Poisoning Effect on the Performance of a Passive Catalytic Hydrogen Recombiner of a Localizing Safety System at a Nuclear Power Plant Equipped with Water-Cooled Water Reactors

A modern Nuclear Power Plant (NPP) is equipped with localizing safety systems to contain radioactive substances and ionizing radiation within the boundaries specified by the design in the event of an accident. To protect the border, a hydrogen removal system is used, including passive autocatalytic hydrogen recombiners. The system prevents the formation of flammable and explosive concentrations of hydrogen by converting hydrogen into water during a reaction with atmospheric oxygen on a catalyst. The main catalyst material is usually platinum with a proportion of palladium. Along with hydrogen, the emergency environment contains specific substances known as catalyst poisons. Poisons reduce catalyst activity and decrease the performance of recombiners. Electron pair donor substances, such as tellurium, are dangerous for the platinum catalyst. The amount of released catalytic poisons at the stage of active zone melting is sufficient to reduce the activity of the catalyst. The level of reduction is estimated by calculations. Aerosol poisons are dangerous in the zone of separated flows near the surface of the catalytic element. Poisons in atomic (molecular) form are dangerous to the catalyst along the entire length of the element. The poison causes a gradual decrease in the productivity of recombiners as the amount of reacted hydrogen increases. The rate of poisoning depends on the type and concentration of the poison, and the mass of active platinum per unit surface area of the catalyst. The calculation shows the possibility of a decrease in the productivity of a passive catalytic hydrogen recombiner due to catalyst poisoning under accident conditions at a Nuclear Power Plant with Water-Moderated Water-Cooled Reactors. Quantitative data on the poisoning of recombiners of the FRand RVK-types are presented. The poisoning effect should be taken into account when selecting the performance of the hydrogen removal equipment of the localizing safety system for a power unit at a Nuclear Power Plant with Water-Moderated Water-Cooled Reactors.

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