A mathematical model is developed for the radiolysis of water vapor and water vapor to which molecular hydrogen and oxygen are added. The model is verified using existing experimental data on the radiolysis of water vapor in a wide range of temperatures and dose rates of ionizing radiation.In our country, we do not have certified software for calculating the consequences of normal and radiation-chemical processes in the first-loop coolant, which in the core is a two-phase system consisting of water vapor and liquid water and containing noncondensing gases, for reactor facilities with boiling water-moderated water-cooled reactors. The lack of such software is due to the complexity of the mathematical model of the thermal radiolysis of a two-phase system. Essentially, such a model is a superposition of three models which interact with one another -the radiolysis of liquid water, interphase mass transfer, and radiolysis of vapor with process additives. The first two models are now quite well developed, whereas there is no satisfactory model for the radiolysis of water vapor under the conditions of the core in a power reactor.The present work is devoted to developing a model of the radiolysis of water vapor and water vapor to which molecular hydrogen and oxygen are added and verifying this model on the basis of existing experimental data in a wide range of temperatures and dose rates of ionizing radiation.There are many works devoted to the radiolysis of water vapor under various conditions, but a mechanism suitable for describing its kinetics, specifically, the kinetics of the accumulation of stable products -hydrogen and oxygen -is described in detail only in [1,2]. It is this mechanism that was used as a basis for developing a model of the radiolysis of vapor and it was supplemented by reactions discussed in later works [3]. The set of elementary reactions, which is used for developing the model, and their parameters from [4] are presented in Table 1. The initial radiation-chemical yield of active particles of radiolysis of vapor and the yield from the decomposition of water, which were determined after the physicochemical stage of radiolysis has been completed, when purely chemical radical processes start to occur in the irradiated system, was assumed to be G H 2 = 0.5, G H = 7.4, G OH = 6.3, G O = 1.1, G H 2 O = 7.4 particles/100 eV. In accordance with the data in [3], it was assumed that the yield is independent of the irradiation conditions in a wide range of values of the external parameters -temperature up to 900 K, pressure from 10 4 to 10 6 Pa, absorbed dose rate up to 10 12 Gy/sec -and types of radiation -from γ rays to the fission products of uranium nuclei.Analysis showed that not all existing experimental results can be used to verify the mechanism describing the kinetics of the radiolysis of vapor. The documentation accompanying the experimental data used for verification must meet strin-

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Hydrazine is a strong reducing agent that has found wide use for removing oxygen dissolved in coolant water in both thermal and nuclear power production. Some power plants with water-cooled, water-moderated reactors [VVI~Rs] use hydrazine hydrate as a source of the hydrogen required to suppress radiolysis of the coolant water in the primary loop.As hydrazine passes through the primary loop and its makeup section of a VVI~R, it undergoes three reactions: oxidation, thermal decomposition, and radiolysis (primarily in the core).Hydrazine Oxidation. When hydrazine either is in pure water or contacts an unoxidized metal surface, it slowly oxidizes with the net reaction N2H 4 + O 2 = N 2 + 2H20.(1)If coolant water containing oxygen and iron oxide suspensions contacts oxidized metal surfaces in a thermal or nuclear power plant, the oxidation process is complex and occurs in multiple stages as follows [1][2][3][4][5]: in the first stage, where there are enough metal (e.g. iron) oxides, the predominant reaction is the reduction of oxides and hydroxides: N2H4+ 6Fe203= N2+ 2H20 + 4Fe304; N2H4+ 2Fe203= N2+ 2H20 + 4FeO; NzH4+ 2FeO= 2Fe + N2+ 2H20; N2H4+ 4Fe(OH)3= 4Fe(OH)2+ N2+ 4H20.Only afterwards is oxygen bound in the reactions: 02+ 4Fe(OH)2+ 2H20 = 4Fe(OH)3; O2+ 4Fe304= 6Fe203.In this mechanism, the metal oxides and hydroxides in essence catalyze hydrazine oxidation, which is described formally by the net reaction (1).The complexity of the process, which includes heterogenous stages with the participation of metal oxides and hydroxides, affects how the hydrazine-oxygen reaction rate depends on the reagent concentrations, the temperature, and pH of the coolant, as well as the presence and amount of catalysts. The maximum rate of this reaction occurs for pH 9-13 [3, 4, 6, 7]; for pH _< 7, hydrazine not only does not decrease the corrosion rate of steel, but increases it [3, p. 192; 6]. The oxidation rate is proportional to the product of the hydrazine and oxygen concentrations [2] and speeds up significantly as the temperature increases [3]. An insignificant concentration of copper ions ( -0.5" 10-6 M) has an extremely strong catalytic effect on the hydrazine-oxygen reaction [5], while iron ions do not have such an effect [2], Iron surfaces, which do not undergo reduction, significantly accelerate the reaction [3].

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