Development and verification of a mathematical model of the radiolysis of water vapor

Abstract

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-

Radiolysis Model Sensitivity Analysis for a Used Fuel Storage Canister

“…Figure 2+1 gives an example where the calculated H 2 yield with time is visually identical with the curves of Fig. 1 of Arkhipov et al (2007). Additionally, in reproducing Table 2 of Arkhipov et al (2007), it was discovered that the calculations should refer to 5+ns pulses rather than the mistyped 0.5+ns stated in the caption.…”

“…Table 2+1. G+values for Air (Bulearcă et al 2010) The reactions, the G+values, and the species considered are the ones typically modeled for atmospheric chemistry (Atkinson et al 2004) and gas treatment applications (Bulearcă et al 2010), as well as for steam radiolysis occurring in nuclear power plant operations (Arkhipov et al 2007). Of course, many other reactions could be considered-the motivation here is to consider a sufficient set to account for H 2 generation and the generation of corrosive products (e.g., HNO 3 , O 2 , H 2 O 2 ) affecting the integrity of the used fuel storage canisters.…”

“…Of course, many other reactions could be considered-the motivation here is to consider a sufficient set to account for H 2 generation and the generation of corrosive products (e.g., HNO 3 , O 2 , H 2 O 2 ) affecting the integrity of the used fuel storage canisters. Initially, 101 reactions from references (Arkhipov et al 2007, Atkinson et al 2004, Bulearcă et al 2010 were considered. The last 10 reactions (102+111) were added for the physical consistency of ensuring the concentrations of charged and unstable species go to zero as the dose rate goes to zero under any conditions.…”

“…Model testing was performed during the radiolysis model development. The reactions modeled for water vapor radiolysis were reproduced from a radiolysis model of water vapor in the first+ loop coolant for boiling water+moderated, water+cooled nuclear reactor facilities (Arkhipov et al 2007). That work reported calculations of radiolytic H 2 production in the temperature range 450+ 900 K, dose rates 500+3x10 11 Gy/sec, and vapor density 0.25+1 g/L.…”

Combined effect of gamma-radiation and pH on corrosion of Ni–Cr–Fe alloy inconel 600

“…No values for the dose rate that a heat exchanger would receive during normal operation have been reported. A gamma-dose rate inside a reactor core (which contains fuel and moderator/coolant) is estimated to be in the range of MGy/h [9,10]. A heat exchanger is located outside a reactor core and should receive a significantly lower dose rate.…”