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In the present research, the possibility of using the electrochemical amperometric sensor with a diffusion barrier, based on yttria-stabilized zirconia electrolyte and two Pt electrodes, for measuring small NO concentration (below 1 vol.%) in nitrogen, air, and О2 + N2 gas mixtures, was discussed. The sensor testing at 450–600°С demonstrated high stability and reproducibility of results and good dynamic characteristics. It was shown that the sensor exhibits specific values of the limiting current for different contents of nitric oxide in the considered gas mixtures that allows precise determining of small NO concentrations. The presence of NO in the gas mixtures containing free oxygen was found to significantly increase the sensor limiting current. The catalytic role of NO molecules in oxygen exchange at the triple phase boundary between the solid electrolyte, electrode, and gas was discussed. Effect of NO2, CO2, and H2O impurities on the sensor performance was studied.

The main results of experimental validation of the operability of passive core cooling systems of nextgeneration VVER are presented. It is shown that the residual heat release can be removed in 24 h on account of the operation of the second-stage water-storage system and the passive heat-removal system. As part of the validation of VVER-TOI passive safety systems the thermophysical properties of boric acid (density and viscosity) were measured experimentally with parameters characteristic for a reactor emergency. Empirical relations satisfactorily describing the experimental data are obtained.

Solid-state electrochemical sensors represent a convenient way for solving various electroanalytical tasks. In this work, we present a comprehensive analysis of binary gases composed of hydrogen mixed with an inert gas (He, Ar, N2). Using the fabricated aerometric-type YSZ-based electrolyte, diffusion coefficients for these binary gases were successfully determined in an electrochemical way in a temperature range of 550 °C–750 °C. The obtained results agree well with literature data, showing that the He+H2 gas mixture with highly volatile components exhibit the highest diffusion coefficients, which are around 2 times higher than that for Ar+H2 and N2 + H2.

Procedure was developed for measuring the diffusion coefficient of hydrogen in its mixture with nitrogen in the temperature range 450–600°C under atmospheric pressure. This is done in an electrochemical cell based on a solid-oxide electrolyte with proton conductivity of composition BaCe0.7Zr0.1Y0.2O3–δ. The procedure makes it possible to trace how the hydrogen diffusion coefficient varies with temperature and hydrogen concentration in nitrogen. It is shown that the hydrogen diffusion coefficient grows with increasing hydrogen concentration, its temperature dependence is of power-law type with n = 1.5, and it is in satisfactory agreement with the theoretical temperature dependence

GE2M-PG test facility was constructed at the JSC “SSC RF-IPPE” for assessment of efficiency of VVER steam generator and investigation of effects of initial conditions of the accident on the processes of heat exchange in the steam generator (SG) tube bundle assembly. The facility was used in two series of experiments with and without removal of the steam–gas mixture (SGM) from steam generator cold collector. Functionality of the steam generator model in condensation mode with different concentrations of non-condensable gases in steam at the SG model inlet and different flow rates of steam–gas mixture removed from cold collector was investigated during the first phase of experiment. Effects of main factors of operational modes on the efficiency of heat exchange processes in the steam generator tube bundle assembly was investigated during the second phase of experiments conducted without removal of steam–gas mixture. The obtained results can be applied for verification of computer codes used in calculation simulation of emergency processes in VVER reactor facility.

The article presents the results of the experimental study of heat and mass transfer processes in an NPP steam generator during the operation of passive safety systems of new-generation VVER reactor installations. At the GE2M-PG test rig in the Leypunsky Institute for Physics and Power Engineering, two series of experiments corresponding to different stages of the accident were completed. In these experiments, the performance of VVER steam generator in the condensing mode with and without the removal of gas-vapor mixture from the “cold” header has been studied. As a result of the first series of experiments, it was found that, for any of the parameters of the emergency process, the steam generator’s power does not drop below 80% of the original value. Furthermore, we revealed that the composition and physical properties of gases in the investigated concentration range did not notably affect the processes in the steam generator. In the second series of experiments without removal of noncondensable gases, the influence of parameters of the emergency process on the efficiency of heat transfer in the steam generator operating in the condensing mode was investigated. In order to study the heat transfer processes, we studied the change of the temperature difference between the media of the first and second circuits in our experiments. We found that the value of the temperature difference depends on both the mass of noncondensable gases accumulated in the tube bundle and their accumulation rate. The accumulation rate is determined by the power of the steam generator and the concentration of gases entering the steam generator. As a result of the analysis of experimental data, we obtained the analytical dependence reflecting change in the power of the steam generator operating in the emergency condensing mode.

The problem of closing the nuclear fuel cycle is not only related to the development of new types of nuclear fuel and the operation of fast neutron reactors, but also to the complex schemes for the pyrochemical reprocessing of spent nuclear fuel (SNF), which, in turn, require adherence to strict process parameters. In particular, this concerns the operation of the reduction of oxidized SNF mainly by metallic lithium. The paper presents the basic scientific principles and the results of experimental verification of the operation of an electrochemical sensor for measuring oxygen in molten salts in pyrochemical reactors for the reprocessing of spent nuclear fuel. The sensor design consists of two combined electrochemical cells based on the solid electrolyte ZrO2-Y2O3 with a common reference electrode. The sensor allows continuous measurement of the oxygen activity in the oxide-chloride melt and the partial pressure of oxygen in the gas atmosphere above the melt directly during the process of pyrochemical processing. Experimental verification of the sensor performance was performed in a reactor with LiCl-Li2O melts at a temperature of 650 ° C. The resource of continuous sensor operation exceeded 500 hours, and the number of thermal cycles without destruction was at least 20. The sensor readings were found to depend on the specified Li2O content in the LiCl melt.

The results obtained from experimental investigations into thermal-hydraulic processes that take place during operation of the passive safety systems used in new-generation reactor plants constructed on the basis of VVER technology are presented. The experiments were carried out on the model rigs available at the Leipunskii Institute for Physics and Power Engineering. The processes through which interaction occurs between the opposite flows of saturated steam and cold water moving in the vertical steam line of the additional system for passively flooding the core from the second-stage hydro accumulators are studied. The specific features pertinent to undeveloped boiling of liquid on a single horizontal tube heated by steam and steam-gas mixture that is typical for of the condensing operating mode of a VVER reactor steam generator are investigated.

In new Russian NPP with VVER reactor in the event of LOCA, provision is made for the use of passive heat removal system for necessary core cooling. In the case of leakage in the primary circuit this system assures the transition of steam generators to operation in the mode of condensation of the primary circuit steam coming to steam generator piping from the reactor. As a result, the condensate from the steam generators arrives to the core providing its additional cooling. The steam generator off-design condensation mode has the following features: undeveloped nucleate boiling on the horizontal tubes heated by condensing steam; natural circulation processes in the both steam generator circuits; low heat fluxes and temperature differences. The experimental study of undeveloped nucleate boiling on the single horizontal tube heated by condensing steam has been carried out in the Institute for Physics and Power Engineering. The experiments have been carried out on the GROT test facility. The heart of the test facility is the single VVER steam generator tube (length l = 10.2 m, outer diameter D = 16 mm, wall thickness d = 1.5 mm). The tube is fabricated of the original stainless steel 08Cr18Ni10Ti. The length and geometry of the test tube corresponded to that of real steam generator. The test facility was equipped with thermocouples enabling the temperatures of primary and secondary facility circuits to be controlled. The experiments were carried out at three heating steam pressures Ps1: 0.21, 0.35, 0.55 MPa. The main task of the research was to study the pressure effect on the process of undeveloped nucleate boiling on the single horizontal tube. On the base of the results of these experiments the empirical correlations for prediction of heat transfer coefficient and heat flux were obtained. The generalizing empirical correlations obtained can be used for the substantiation of work heat-exchanging equipment of NPP with VVER reactor in the condensation mode, and also can be applied to the verification of computer codes.