Vol 66, No 5 (2019)

The article describes the basic models laid down in the second version of the EUCLID/V2 integrated code developed for carrying out end-to-end analysis of severe accidents in liquid metal cooled reactors. Brief information about the basic analogs of the code is given. Unlike the first version of the code, its second version includes additional tools for analyzing design-basis and beyond-design-basis accidents involving fuel pin, fuel assembly, and reactor core failures. To this end, the code is supplemented with additional modules using which it is possible to calculate fuel rod tightness failure as a consequence of its melting, escape of fission products into the coolant, their transport over the circuit, and release into the nuclear power plant rooms. The code also incorporates modules for calculating the core failure processes. Special attention is paid to the physical models for calculating the core materials' melting processes, motion of the produced melt, its interaction with the coolant and with other materials, and propagation of fission materials. For calculating the core failure processes, a multicomponent 3D model has been implemented. The methods used for calculating heat transfer and friction between the components are based on well-proven analytical and empirical relations for determining the heat transfer and friction coefficients. The coefficients presented in the article also depend on the obtained multicomponent flow motion regime and the type of components (metal and ceramics). The algorithms governing joint operation of the thermomechanical, thermal-hydraulic, neutronics, and the fuel rod thermal failure module are described. Emphasis is placed on data exchange methods in the course of an accident in the reactor. The approaches used for calculating the transport of fission products in the coolant and in the NPP rooms are presented.

The article deals with one of the most crucial and, at the same time, problematic stages of implementing the uncertainty analysis of thermal-hydraulic calculations by the GRS method—the validation of the statistical characteristics of model uncertainties—namely, of the circuit thermal-hydraulic block’s closing relations. The above relations developed, as a rule, on the semiempirical approach, are one of the main sources of uncertainty of the results calculated by the code. A task of developing the method proposed by the authors earlier that allows performing the validation procedure using verification technology and objective statistical criteria was set. The method in question allows going from an expert evaluation to the objective assessment of the model parameter uncertainties, thus enhancing the objectivity of the calculated results obtained within the framework of the GRS method. Particular problems are formulated the solution of which expands the capabilities of the method to use experimental information and to assess the uncertainties of the model parameters that cannot be directly measured experimentally. This, in turn, allows using the method for validation of the uncertainty of all most-critical model parameters of the design code. The stages of the proposed method are set forth sequentially followed by discussion of the topical problems that arise at every stage. Using practical examples, the ways of solving the formulated problems are demonstrated. The results obtained using the method for evaluation of uncertainties of a series of model parameters (closing relations) of the KORSAR thermal-hydraulic design code are provided. The results are recommended for use when analyzing uncertainties within the framework of the KORSAR code by the GRS method. Moreover, the proposed method can also be applied to other design codes.

A technique for calculating the standardized indicators characterizing the thermal efficiency of combined-cycle power plants (CCPPs) using correlation equations linking the values of these indicators with different external conditions is proposed. The correlation equations were written using the results from measuring the outdoor air and cooling water temperatures; air barometric pressure and humidity; fuel (natural gas) flowrate, heating value, and density and load in steady-state operation modes of the CCPPs and their equipment. It is usually sufficient to have a sample with three groups each representing 15–20 operating modes: under winter conditions at an outdoor air temperature of –20 to –30°С, under summer conditions at an outdoor air temperature of above 20 to 30°С, and at an intermediate temperature of ±5 to ±7°С. In each group, it is sufficient to have two operating modes each with loads close to 0.5, 0.6, 0.7, 0.8, and 0.9 of the maximal value, and 5–10 operating modes with a close-to-nominal load. It is shown, taking a single-shaft 400 MW CCPP as an example, that the correlation equations adequately (with errors equal to approximately 1%) describe the results obtained experimentally in the normal operation modes. The developed technique opens the possibility to determine, in a more accurate and simple manner, the standardized heat rates and other technical-economic indicators of fuel utilization without using an excessive number of corrections able to distort the result. The technique can also be used for estimating the changes of CCPP indicators as a result of taking some or other measures in them.

Investigation tests of the P-134 heat-recovery steam generator (produced by PJSG Zio-Podolsk) used as part of the PGU-230T combined-cycle power unit at the Chelyabinsk combined heat and power plant no. 3 (CHPP-3) were carried out, as a result of which experimental data on the steam generator thermal parameters have been obtained, and adequacy of the thermal–hydraulic design analysis model developed by PJSG ZiO-Podolsk has been confirmed. A description of the heat-recovery steam generator is given along with schematic arrangements of experimental instrumentation, test conditions and techniques, and experimental data processing methods. A procedure and computer program for estimating the steam generator thermal parameters, and a procedure for reducing the test results to design conditions are elaborated. It has been determined that the total thermal power of heating surfaces in the steam–water path deviates from the steam generator total thermal power directly measured at the boundary balance sections by no more than 0.84%. The steam generator thermal power values determined with reference to the steam–water and gas paths differ from each other by no more than 1.7%. The steam generator thermal power obtained in the tests differs from its design value by no more than 2.4%, and it should be noted that its value measured in all operating modes was higher than its design value. The design thermal power values of the high-pressure loop heating surfaces reduced to the test conditions differ insignificantly (and toward increasing) from their actual values. The obtained results demonstrate that the analysis models can be used for reducing the test results to the heat-recovery steam generator operating conditions (parameters) at which the conformity of their values is established for confirmation (assessment) purposes, in particular, in carrying out warranty tests. It has been shown that the heat recovery steam generator’s thermal power reduced to the warranty conditions that was obtained in all test modes is somewhat higher than the design thermal power under the warranty conditions.

The results of a comprehensive experimental study of the boiling of water subcooled to the saturation temperature in a channel are presented. This technology is used to remove extreme heat fluxes in modern equipment. An emphasis is placed on the study of the characteristics of vapor bubbles, their changes under the effect of various regime factors, and characteristics of the heating surface. For the realization of the goals, a high-speed video of the process was used. Experiments were carried out with distilled deaerated water at atmospheric pressure, heat flux densities of up to q = 8 MW/m², subcooling of the liquid to the saturation temperature of Δt_s = 30–80°C, and the flow velocity of the liquid of up to w = 0.7 m/s. Smooth and structured surfaces with coatings, most of which were produced by microarc oxidation, were used in the experiments. Significant subcooling of the liquid to the saturation temperature is shown to cause a deep deactivation of the active nucleation cites after the collapse of the vapor bubble and spatial and temporal randomness of the distribution of the nucleation cites over the heating surface. The bubble size distribution, the density of nucleation cites that is approximately proportional to the heat flux density, the bubble lifetime, and the duration of individual stages of its life cycle are determined. A picture of the bubble collapse is clarified. The subcooling of the coolant to the saturation temperature is shown to be the strongest among the parameters that determine the boiling of the subcooled liquid. The phenomenological Snyder–Bergles model of the boiling process was established to agree best with the measurement results. Such engineering aspects of the problem as the choice of limiting design parameters of the cooling system and the use of coatings for boiling enhancement of a subcooled coolant are considered.

The current state of exploitation of low-potential thermal waters of the East Ciscaucasia Artesian Basin has been evaluated. Low-potential waters, which are the only source of water supply for a considerable number of consumers in the North Caucasus, are being exploited in an extremely inefficient way with at most 20% of the allocated resources being utilized to the fullest extent. Abusive exploitation of the wells resulted in the bogging of large areas around them, depletion of water resources, and deterioration of the latter as a consequence of backflow of low-quality water from adjacent horizons into those being exploited. The quality of the water has drastically deteriorated; in most wells, contaminants, such as arsenic and various organic compounds, have been detected in quantities that considerably exceed the maximum permissible concentrations set for potable water. These thermal waters are not being used for generation of heat and power since their temperature is too low for heat and hot-water supply purpose. However, the resources of low-potential waters are sufficient to solve the problems of heat and hot-water supply and to provide a considerable number of consumers in the region with potable and process water provided that these resources are exploited in a sensible way using new complex technologies. Complex engineering systems comprise a system of heat pump plants in which the low-potential heat of thermal waters is utilized and a chemical treatment plant in which the cooled water is purified from contaminants, thus raising its quality to the potable water standard. The designs and technological parameters of the chemical treatment plants differ depending on the composition and amount of contaminants. The complex systems allow utilization of the product of thermal artesian wells to the fullest possible extent and large-scale introduction of such systems will facilitate the solution of environmental and economic problems in the region and improve sanitary, hygienic, social, and living conditions of people.

The problems of bellows expansion joints conditioned by their design features and the quality of the heat carrier are considered. It is testified that typical damage of bellows expansion joints are deformations, changes in geometric characteristics, and through defects of structural elements. Prevention and timely detection of damaged bellows expansion joints is an important task of the heating system’s operation. Examples of damage to bellows expansion joint elements are presented, including those with corrosive destruction of pearlitic steel corrugated inner layers and outer high-alloyed steel corrugations. Some survey results are presented and factors are analyzed that may affect the damageability of bellows expansion joints of the main heating network pipelines at PAO MOEK¹. The causes and dominant damage mechanism of bellows expansion joints, caused by the formation of crevice defect with penetration of the heat carrier into the inner space of the pearlitic steel corrugated layers, have been established. Practice has shown that most of the damage is detected in pressure testing and is associated with mechanical deformations of the bellows without depressurization and without unsealing and loss of the heat carrier. Four main corrosion and damage stages of heating system bellows expansion joints are identified. It is proposed, depending on the initial and operating conditions, to consider possible scenarios of a two-stage mechanism of destruction of bellows expansion joints, including the development of a crevice defect up to the through leakage of heat carrier into the bellows interlayer space and corrosion damage to the inner corrugated bellows surface. Recommendations to prevent damage to bellows expansion joints of heating systems are provided.

Make-up water is treated at thermal power stations (TPS) with high-pressure or superhigh pressure boilers using membrane processes implemented in ultrafiltration, microfiltration, or reverse-osmosis (RO) units. Among the criteria of the efficiency of reverse osmosis units is the amount of highly mineralized effluents (or concentrate). At present, the RO concentrate is disposed of at TPSs by discharging it into an industrial sewage system in accordance with the applicable standards on the salt content limit of waste water, routing it into a district heating network, or returning it into recirculation water supply systems, decreasing as far as possible the volume of the discharged concentrate which is to be reused, for example, in regeneration of Na-cation exchangers installed upstream of the reverse-osmosis unit. The adsorption process is proposed for treatment of the reverse-osmosis concentrate using sludge from the makeup water treatment. The characteristics of carbonate sludge are presented. The regularities of adsorption of sulfate- and chloride-anions from the RO concentrate by carbonate sludge are described. An adsorption isotherm was obtained. The mechanism of adsorption on a sorption material is proposed. The effect of pH on adsorption of sulfate- and chloride-ions by a sorption material was investigated. A system is proposed for the treatment of the concentrate from the RO units at the Kazan Cogeneration Power Station TETs-2 to remove sulfate- and chloride anions using a three-stage adsorption method with a counter-current injection of the sorbent, namely, the carbonate sludge. The calculated values of the consumption of the sorption material required to achieve the desired residual concentration of sulfate- and chloride-anions in the treated water are presented. The economic effectiveness from implementation at the Kazan TETs-2 of the adsorption treatment of the RO concentrate by carbonate sludge to remove sulfate- and chloride-ions is estimated.