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-

An approach to simulating the water-chemistry regime for transient and stationary operating states of a nuclear power system is proposed. The approach is based on the designer's philosophy. The first loop of the nuclear power system is divided into standard units. The special features of the reactor design and the crux of the problem being solved determine the number of units and the interaction between them. The units can be structural components of the loop as well as coolant components. The thermochemical and radiation-chemical transformations of the components of the water coolant are simulated at each unit. The interaction between the physicochemical processes at the units is expressed in the flow of the coolant components between them. The approach developed is illustrated on the analysis of the water-chemistry regime in implementing a passive safety system -a promising solution geared toward increasing the operational safety of the first loop of a nuclear power system.The development of innovative nuclear power systems with two-phase coolants entails the development of models, methods, and programs for validating the water chemistry with prescribed parameters. This requires describing the following:• the influence of the topology and noncondensing gases on interphase mass transfer and transport of coolant components along the first loop of the nuclear power system; • the radiation-chemical transformations of the cooling water in the first loop, taking account of the composition of the reactor radiation and the thermophysical characteristics of the liquid and vapor phases; • the boundary processes in the system water coolant-structural material of the first loop with prescribed radiation, thermophysical, and hydrodynamic conditions in the loop, composition of the coolant, and properties of the materials. The simulation of the chemical transformations occurring with the substances dissolved in the water under the action of fast neutrons, γ rays, and charged particles is based on the currently generally accepted theory of indirect action of radiation [1]. A system of differential equations, whose coefficients are the rate constants and activation energies of the elementary reactions, the primary yield of the products of radiolysis of water, the transfer of energy per unit length, the absorbed

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A model of an interphase transfer of stable products of the radiolysis of water in boiling coolant is developed taking account of the intensity of their delivery to the interphase boundary in the liquid phase and removal into the vapor phase with vapor generation on the interphase surface. A computational study is made of the radiolysis of the coolant and interphase transfer of the products of the radiolysis of water in the core and on the pulling section of BWR of the Oskarshamn-2 nuclear power plant in Sweden. A comparison of the computational data with the results of the technical measurements of the coolant composition of the BWR at the Oskarshamn-2 nuclear power plant showed that the accumulation of stable products of the radiolysis of water in the vapor-gas phase of the coolant is determined by the kinetics of radiolysis in the liquid phase, the concentration of the oxygen-containing components in the liquid phase is due to the present of hydrogen peroxide in it.The present trend in the development of modern water modern and cooled reactors is to increase their operating efficiency by increasing the energy density of the core, which eliminates the possibility of short-time boiling of the coolant in individual streams at the core top. This raises questions concerning the particulars of the water-chemistry regime in the first loop under these conditions. Even though numerous experiments have been performed on operating reactors, it is difficult and sometimes impossible to use the data obtained to verify models of radiolysis and mass transfer in the core. This is because the conditions under which these data were obtained are not adequately described in the publications. As a rule, the precise thermohydraulic conditions in the core, a detailed composition and spectrum of the radiation, the composition of the water coolant, and other particulars are not presented in them. The best experimental data were obtained in 1979-1981 at the BWR in the Oskarshamn-2 (Sweden) during a study of the influence of the metering of hydrogen into the feed water on the content of oxygen in the circulation loop [1]. A detailed description of the data is presented in [2].We have attempted to use the data of [1] for verifying the model of the physicochemical processes in the two-phase water coolant of light-water reactors and determine the particulars of radiolysis and mass transfer in the presence of steam generation on the interphase surface.Radiolysis of a liquid and steam, interphase mass transfer, and transfer of the products of radiolysis in the phases were modeled using the approach described in [3], making provisions for the interaction of the integral systems code with the partial models of the physicochemical, transport and hydrodynamic processes. The RELAP5/mod3.3 improved evaluation codes was used as the systems code [4]; the H2O-rad Version 2.7.0 module of the MORAVA N2 code was used to

Room-temperature γ radiolysis of water solutions of ammonia in the presence of hydrogen peroxide is studied. It is found that in de-aerated solutions the yield of hydrogen peroxide decomposition is 3. 8-5.5 mol/100 eV depending on its initial concentration. In the absence of hydrogen peroxide, the yield of the decomposition of ammonia is 0.34-0.39 particles/100 eV; adding hydrogen peroxide to the solution increases the rate of decomposition of ammonia and saturation of the solution with hydrogen decreases it. The data obtained are used for mathematical simulation of the influence of hydrogen peroxide on the composition of the first-loop coolant of a hypothetical ship reactor facility with VVER where equipment corrodes with hydrogen being formed. It is shown that adding hydrogen peroxide to the coolant in molar concentration equal to that of corrosion hydrogen decreases the stationary concentration of hydrogen and ammonia to the level characteristic for the case where there is no equipment corrosion with hydrogen being formed in the loop.There have been cases where during the operation of ship reactor facilities with VVER the maximum admissible concentration of ammonia in the first-loop coolant was exceeded [1, 2] because the zirconium materials in the elements of the core undergo corrosion and a substantial amount of hydrogen is formed. Ammonia forms in the core as a result of radiation-chemical synthesis from dissolved nitrogen and corrosion hydrogen. One way to decrease the concentration of the latter and, correspondingly, ammonia in the first-loop water of VVER could be its radiation-chemical removal by introducing a water solution of hydrogen peroxide into the coolant. This method is attractive because new reagents are not introduced, since the hydrogen peroxide is a product of the radiolysis of water and is unavoidably present in the first-loop coolant of any light-water nuclear power reactor [3].Let us examine the equation of material balance for radiolysis of water solutions of ammonia in a closed single-phase system [4] for the specific case of the radiolysis of water coolant, initially containing dissolved ammonia, nitrogen, hydrogen, and hydrogen peroxide. For prolonged irradiation of water in a closed system, initially containing only dissolved ammonia, a stationary state is established with a stationary concentration of the products of radiolysis given by the relation [H 2 ] st = [H 2 O 2 ] st + 2[O 2 ] st + 3[N 2 ] st . If water initially containing dissolved ammonia and nitrogen is irradiated, then [H 2 ] st = [H 2 O 2 ] st + 2[O 2 ] st + 3[N 2 ] st -3[N 2 ] ini ,