Particulars of radiolysis and mass transfer in two-phase water coolant of a nuclear power facility with steam generation at an interphase surface

Abstract

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