Vol 66, No 7 (2019)

For assessing the core critical heat flux ratio in VVER-type nuclear reactors, the lattice computation code TIGRSP (steady-state thermal and hydraulic analysis of parameters in fuel rod bundles) is used. Despite the fact that quite a large amount of verification studies has been accomplished and that the code has passed the certification procedure, work on improving the code capabilities is still being continued. One of the modern tendencies is the wide-scale involvement of CFD codes for studying local parameters in fuel assemblies (FAs). Along with comparison with experimental data, it is advisable to carry out cross verification of lattice codes with the results of 3D thermal-hydraulic computations for conditions for which experimental data are either lacking or limited for some or other reasons. This article considers thermal-hydraulic processes during coolant flow in a 19-rod assembly with parameters close to the nominal conditions in the FAs of a VVER-1000 reactor. The 3D model is verified with respect to empirical formulas and experimental data. Based on the results of test and verification computations, we determined the mesh and turbulence model parameters using the ANSYS CFX code by means of which it is possible to obtain reliable results in estimating the hydraulic characteristics of FAs fitted with spacer grids, heat transfer in the single-phase region, and coolant flow distribution over the FA cross section. The CFD computation of coolant flow for the 19-rod assembly is carried out, and the coolant mass velocity and temperature in different sections over the length and corresponding cells of the TIGRSP code are calculated. The TIGRSP code has been verified against experimental data and taking into account the CFD simulation of the 19-rod FA, and a software module for graphically visualizing the lattice code output results has been developed. The presented data can be used for verification of thermal-hydraulic codes and in elaborating the design of FAs for VVER-type reactors.

The processes through which the α-emitting radionuclides contained in the primary circuit of a propulsion reactor are transferred in the circuit and removed from it in the standard ion-exchange filters are studied. The correlation between the behavior of transuranium elements and iron-containing corrosion product compounds in the primary circuit is considered. During reactor operation at steady power levels, α-emitting radionuclides reside, like iron compounds, predominantly in deposits on the circuit equipment surfaces. When hydrodynamic disturbances occur, these deposits transfer into coolant in the form of insoluble particles, thus intensifying the transfer of α-emitting radionuclides over the circuit. It has experimentally been found that the average deposition time of particles containing α-emitting radionuclides is larger than that of iron-containing particles (their deposition constants are equal to 0.6 h^–1 and 0.9 h^–1, respectively). This fact gives grounds to suppose that α-emitting radionuclides are nonuniformly distributed in corrosion product deposits and transfer into the coolant predominantly in the composition of particles having a smaller mean radius than that of iron-containing particles. As a result, the reactor’s standard ion-exchange filters show a relatively poor purification efficiency of α-emitting radionuclides (the purification constant is approximately 0.1 h^–1 vs. 0.2 h^–1 for corrosion product particles as a whole). The metering of hydrazine into the coolant results in that the repeated deposition rate of particles containing α-emitting radionuclides decreases by a factor of seven, due to which up to half of α-emitting radionuclides transferred into the coolant under the effect of hydrodynamic disturbance can be removed from it in the filters.

The results from experimental investigation into hydrodynamics and heat transfer in a two-phase natural circulation loop (NCL) under atmospheric pressure are presented. The experiments were carried out for liquids having essentially different properties: water, ethanol, and perfluorohexane C₆F₁₄ (the product trademark is FC-72). The circulation velocity in the NCL is not known in advance but is a complex function of the specified parameters (heat flux and liquid temperature at the heated section inlet) and of the two-phase flow internal characteristics. The liquid temperatures at the heated section inlet, the wall temperature over the section height, and also the circulation velocity were measured in the experiments at a specified heat flux; in addition, the two-phase flow at the loop riser leg outlet was filmed on video. The experiments and analysis have shown that flow hydrodynamic instability (circulation velocity pulsations) is really unavoidable in a two-phase NCL. Hydrodynamic instability with a high circulation velocity amplitude and with the occurrence of backward flows is typical for regimes involving significant liquid subcooling values at the heated section inlet and for NCLs containing an extended part with single-phase convection. This instability, which is characteristic for experiments with water, is due to the displacement of the boiling incipience section over the section height; the instability also persists at small subcooling values but with a low pulsation amplitude. Under the developed saturated liquid nucleate boiling conditions (at high heat flux values), the circulation velocity and wall temperature pulsations have small amplitudes, and the flow can be regarded as stable. In the experiments with perfluorohexane, the smallest wall temperature and circulation velocity pulsations were pointed out, which is attributed to a relatively high value of reduced pressure. In the experiments with ethanol, instability occurs in the developed nucleate boiling region (q > 35 kW/m²); this instability is caused by periodically alternating two-phase flow structure (regime). A procedure for calculating a low-pressure NCL is developed, in which the two-phase flow’s local parameters (void fraction, phase velocities, and pressure) are calculated according to a modified homogeneous model (taking into account the phase distribution factor and phases slip) and a dispersed-annular flow model taking into account the droplet entrainment and deposition phenomena. A comparison of the NCL calculation results with the experimental data obtained for three different liquids has shown that they are in good agreement with each other.

Modern gas turbines have high efficiency. A further increase in their economic efficiency can be achieved, on the one hand, by enhancing the accuracy of the parameter prediction at the design stage and, on the other hand, by the possibility of improving the design for different components of the flow path based on the results of calculating the complicated viscous spatial structure of the flow. One of the tools for enhancing the efficiency of gas turbines is the minimization of the rotor-tip leakage, the rate of which is reduced by shrouding the rotor blades. In particular, using numerical methods and software tools based on the former, one can perform thorough computational analysis of the vortex structure of the flow in the vicinity of the tip shroud and sufficiently accurately determine the rotor-tip leakage rates and other parameters of the stage. Such an approach allows a more accurate assessment of the leakage than semiempirical approaches used in practice. In particular, the assessment by the correlation dependence showed that the leakage rate for the tip shroud design in question with a tip clearance of 5 mm exceeded the leakage rate calculated using the method that considers the specific features of the tip shroud design and the vortex structure of the flow in the vicinity of it by 8.65%. As exemplified by the last-stage rotor blade of a stationary gas turbine, the possibility of controlling the leakage of the main flow through the tip clearance is demonstrated based on results of a numerical experiment.

This is the fourth paper in a series of publications on the experimental investigation of fuel-air mixture combustion in a combustion chamber (CC) with two combustion zones set in a series with an outlet temperature ranging from 1550 to 1700°C and meeting the requirements for NO_x and carbon oxide emissions. The results of the experimental investigation into combustion of gaseous fuel CS comprising two combustion zones set it a series, each with its own burner unit, are presented. The first burner unit (BU1) is typical for low-emission combustors. It has swirlers, a premixing zone, and pilot and main burners. The premixed fuel-air mixture (FAM) is fed to the BU1 inlet. The second burner unit (BU2) is located downstream of the first combustion zone and is fed with FAM with a fuel concentration equal to or higher than the fuel concentration in the first combustion zone. The kinetic fuel combustion whose rate depends on the kinetics of the fuel oxidation reaction rather than on the rate of migration of the reacting components to the flame surface by molecular or kinetic diffusion (as in case of diffusion combustion) occurs in the first and second zones. The second burner unit has its own premixer. In the second zone, the fuel burns in a high-temperature environment at a reduced oxygen content. Four CS configurations with different lengths of the first and second combustion zones were investigated experimentally. The first configuration with single-zone fuel burning is the base one. In the other three configurations, the length of the first and the second zone varied (with the total length of the liner being the same). The results of optimization of the FAN between two sequential combustion zones are presented. The best length of the second zone minimizing NO_x and CO emissions at a CC outlet temperature from 1550 to 1700°С was found.

The Federal Law of July 21, 2014, no. 219-FZ “On Amendments to the Federal Law ‘On Environmental Protection’ and individual legislative acts of the Russian Federation” established new principles of environmental policy providing for a substantial reduction of the negative anthropogenic impact on the environment. For this purpose, objects of Category I have been identified that have a significant negative impact on the environment and are related to the areas of best available technologies (BATs). For the methodological support of switching heat and power enterprises to BATs, a BAT reference document (BREF) 38-2017 “Combustion of Fuel in Large Plants for the Purpose of Energy Production” has been approved. Its task is to determine a list of marker pollutants, technological indicators of pollutant emissions, and best available technologies recommended for introduction at thermal power plants (TPPs) in order to reduce harmful emissions into the atmosphere. The article is devoted to the cost estimation when switching to best available technologies—one of the most acute issues of the power industry. The article presents the main provisions of the methodology for estimating capital and operating costs in switching thermal power plants to BATs, which were developed during joint research of the EIPC and MPEI. The approach proposed in the framework of the developed methodology can significantly reduce the amount of information analyzed and ensure the high reliability of estimates at the same time. The volume of representative samples necessary for a correct cost estimation of implementing measures to reduce power plants' harmful emissions at facilities that fail to meet the BAT requirements is calculated. The range of total costs for the implementation of environmental-protection measures at existing power facilities that do not comply with the BAT principles in the wider heat and power industry has been determined.

An analysis of water utilization systems at thermal power plants (TPPs) shows that highly mineralized effluent waters are mainly generated at these facilities by their water-treatment plants. Highly mineralized alkali liquid waste is presented by the products from continuous and periodic blowdowns of thermal demineralization systems and drum boilers, by spent anion exchange filter regeneration solutions, and by alkali concentrates from reverse osmosis plants. In view of the fact that the alkali used in technological processes has quite a high cost, it is economically expedient to subject alkali effluents to processing with the extraction of alkali for repeatedly using it in the production cycle. The article presents the results obtained at a TPP from experimental investigations into processing of highly mineralized alkali–salt solutions by means of electromembrane technology. The experimental investigations were carried out using the EMA-100 laboratory electromembrane apparatus and included two series of tests: a sequential diffusion–dialysis extraction with concentration by electrodialysis and a single-stage concentration by electrodialysis. As a result, a concentrated alkali solution and partially demineralized softened water were obtained. An analysis of the qualitative and quantitative compositions of the obtained products has shown the effectiveness of the proposed electromembrane processing arrangements, because an alkali solution suitable for its repeated use in the TPP water-treatment cycle was obtained in both series of tests. However, it should be borne in mind that single-stage concentration by electrodialysis is a more economically efficient and simple method, which provides high throughput and yields solutions containing satisfactorily separated alkali and salt components.