Thermal Engineering最新文献

A description is given of the model of formation of iodine oxide nanoparticles in the volume of the containment of a nuclear reactor during radiation-chemical reactions and clustering with subsequent formation of nanoparticles. The results of test calculations are presented. Nanoparticles of radioactive iodine oxides pose a potential hazard as a source of long-term radiation exposure to NPP personnel. They also penetrate outside the power plant through the air-ventilation system even if the enclosure remains sealed. In addition, calculations have shown that the formation of radioactive iodine oxide nanoparticles is closely related to the formation of volatile iodine compounds in the gas phase. Moreover, the intensity of formation of the latter depends significantly on air humidity. The main feature of the proposed model is the consideration of the kinetics of phenomena for processes in both the gas and aerosol phases when exposed to ionizing radiation on oxygen and water vapor in the air. The main result of the calculations is confirmation of the fundamental possibility of the formation of aerosol nanoparticles consisting of iodine oxides in a humid atmosphere even with a relatively low dose rate of radiation energy absorbed by the air. At the same time, radiolysis of water vapor has a weak effect on the size and concentration of iodine oxide nanoparticles. However, taking into account the chemical interaction of radiolysis products, in particular hydrogen radicals, induced by water vapor radiolysis, significantly affects the formation of volatile iodine compounds with hydrogen: HI and HOI. The obtained results, despite their preliminary nature, are important since they indicate the inevitability of the formation of suspended nanoparticles of iodine oxides and hydrogen iodide in the atmosphere of the reactor premises in the event of emergency situations with the release of radionuclides beyond the first circuit of the reactor. Therefore, this mechanism must be taken into account when developing models of the formation and behavior of fission product aerosols at NPPs.

Operation of nuclear power plant units is accompanied by the development of various metal degradation mechanisms (MDM) under the influence of the working environment. Prevention of damage and elimination of sudden destruction of equipment and pipelines (E&P) at operating nuclear power plants depends on the timely identification of those elements and units in which the preconditions for the manifestation and intensification of metal degradation mechanisms are created. In this case, the search for the causes of damage to pipeline lines and equipment parts should be based on the determination of the dominant MDM. The effectiveness of the technical measures being developed to restore and prevent similar damage in the future depends on the correct solution to these problems. Despite significant experience and accumulated statistical data on damage to the metal of the working contours of nuclear power plant units, the establishment of identification features and the detection of dominant MDM in the operating conditions of turbine installations of nuclear power plant units remain highly relevant. This is confirmed by the existing differences in approaches to the classification of MDM and the lack of a clear methodology for their identification when detecting defects and analyzing cases of damage to pipeline elements and equipment. Due to the complexity of the physical and chemical processes and patterns of MDM, their deep and fairly large-scale study is required; therefore, as a rule, the study of a specific MDM is carried out by separate specialized scientific organizations and institutes. This circumstance makes it difficult to form a unified approach to their systematization and classification in order to obtain a complete picture of the dominant mechanisms of damage to E&P turbine installations of nuclear power plant units. At the same time, the achievements of recent years in this area make it possible to formulate more advanced criteria and recommendations for classification and identification of MDM, which are advisable to use in practice, including in the development of industry guidance documentation on this topic.

More accurate evaluation of the energy loss as a consequence of fluid leaks through the clearances between the rotor and stator of turbine machines is a topical problem, which can be solved through more accurately assessing the shroud clearance area by applying a leak flow normal cross section. The article presents the results obtained from measurements of gas dynamic parameters in the low-pressure cylinder (LPC) of a high-capacity steam turbine in the last stage tip zone with improved active protection of the rotor blades against erosion. Flow traversing results have confirmed that, near the stage top at the outlet from the radial clearance between the blade row cylindrical shroud and fins of a three-chamber ledgeless seal (i.e., with the same clearances), the wet steam (two-phase medium) leak direction differs from the axial direction in the turbine and is mainly governed by the working medium swirling in the diaphragm nozzle vane channels and mutually opposite influence of rotation of the shroud and of the main flow from the running cascade channels. The leak flowrate is evaluated by using the flow parameters at the seal outlet and the gas dynamics equation with taking into account the medium compressibility. In estimating the two-phase medium flowrate, the following corrections were calculated: the flowrate coefficient increment caused by the flow dispersity, a correction characterizing the influence of initial wetness and the phase slip ratio. Taking into account the coefficients and corrections is conductive to more accurate description of flow through the seals. The wet steam leak flowrate assessment is approximate in nature because it was carried out proceeding from a simplified physical model describing the two-phase medium outflow. With the jet flowing out at an angle of 35° with respect to the circumferential velocity positive direction, the leak flowrate from the shroud seal at the nominal load expressed in fractions of the wet steam medium flowrate through the LPC last state amounted to (overline {{{G}_{{{text{shr}}}}}} ) = 0.017. The obtained study results are used in designing the wet steam stages of the LPCs of advanced turbines for thermal and nuclear power plants.

The purpose of the study was development of a technology for the extraction of a carbon-rich concentrate suitable for use as an energy fuel from solid products of municipal waste pyrolysis (SPMWP). To do this, the effect of reagents and different flotation conditions on the yield and quality of the carbon-rich concentrate was investigated. The results are presented of the experimental study into the features of the SPMWP flotation process. A relationship has been established between the SPMWP fraction size, the yield of carbon-rich concentrate, and its quality. The fact has been demonstrated that SPMWP flotation characteristics can be improved by ultrasonic dispersion of flotation agents in water and production of concentrates containing, depending on the size distribution of SPMWP particles, from 60 to 67% of combustible matter. Thermogravimetry and differential scanning calorimetry methods have revealed that the combustible matter of the concentrate consists of 65% carbon and 35% volatile carbon-containing compounds. According to the results of X-ray phase analysis, the main water-soluble salts of SPMWP are chlorides of potassium, sodium, and calcium sulfate. As to its heating value (q = 18.4 MJ/kg), the obtained combined concentrate is comparable to coal and can be considered as a renewable energy source since, according to forecasts, the annual increase in the amount of municipal solid wastes (MSWs) will be from 1 to 7%. A schematic diagram of material flows for processing 100 t of SPMWP has been constructed on the basis on the results of performed studies. An additional economic effect can be obtained by using hydroseparation at the stage of municipal waste sorting to separate crushed glass, as a result of which large SPMWP particles may be sent to flotation after grinding.

The potential scope of application of the ammonia-ethanolamine water chemistry in the secondary circuit of a nuclear power plant (NPP) with a VVER-1200 reactor during pilot commercial operation and normal operation is examined. The water chemistry conditions during pilot commercial operation is controlled by an individual scenario for preparing the power unit for commissioning. An initial high content of iron in the steam generator feedwater is observed at all nuclear power plants. Dosing corrective reagents (such as ammonia, hydrazine, and ethanolamine) at NPP power units VVER-1200 reactors maintains their recommended concentrations and the pH range in the feedwater and blowdown water of the steam generators. A comparative analysis of the water chemistries at NPPs with VVER-1000 and VVER-1200 reactors has revealed no considerable differences between corresponding water chemistries as to the regularities of mass transfer of corrosion products, previously identified dependences of iron concentrations on pH, and their changes with time. A new factor is a sharp decrease in the iron concentrations in the steam generator feedwater (below 1 μg/dm³) at рН₂₅ above 9.45 and in an electrical conductivity of the H-cation treated feedwater sample below 0.3 μS/cm. With the selected water-chemistry and the temperature and heat flux maintained at the VVER-reactor, the factors limiting formation of deposits on the heat-transfer tubes of the steam generator are the concentration of iron products and pH of the working fluid. Data on the fouling of heat-transfer tubes of the steam generator suggest that a stable water chemistry in the secondary circuit allows us to schedule much longer washing intervals for the VVER-1200 steam generators in comparison with those for other VVER-reactors. A further reduction in the mass transfer of corrosion products can be attained by replacing pearlitic steels with low-alloy steels having a chromium content of 1.5 to 2.5% for the manufacture of steam pipelines and individual sections of the feedwater path downstream of the deaerator. The results of operation comply with the main conclusions that were made in developing a model for prediction of corrosion and mass transfer in the secondary circuit of a VVER-reactor and corroborate the feasibility of its application in the design and analysis of water chemistry data during operation of the power unit.

The role of solar and wind energy in the current processes of decarbonization of the Russian electric power industry is considered. The issues of the formation and further development of renewable energy, which can make up a significant share of the country’s energy balance thanks to the legislation introduced to stimulate its implementation, are discussed. The rates of commissioning of renewable energy-generation facilities (hereinafter referred to as renewable generation) by region are analyzed, and trends towards reducing capital expenditures in the construction of both solar and wind grid power plants are assessed. An important feature of renewable generation is its stochastic nature, which can cause certain problems when transmitting energy to electrical networks and requires the adoption of special measures to increase the share of renewable energy sources in electrical networks and additional costs to ensure it. Abroad, where a significantly greater path has been taken in the development of the industry, the introduction of grid energy-storage devices, methods for converting surplus energy generated by renewable sources into various useful products and other measures are widely discussed as such measures. In Russia, the overall share of RES in the energy balance is still quite small, but it has already reached threshold values in some regions, at which several pilot projects are being implemented using electric energy-storage devices in both network and autonomous systems. The article provides estimates of the contribution of grid solar and wind power plants to replacing energy from traditional sources and reducing greenhouse gas emissions, and examines the problems and prospects for further development of the industry, primarily from the point of view of the need to reconstruct the grid infrastructure.

Abstract—An analysis of the relationships for calculating the thermal properties of liquid lead (hereinafter referred to as lead) was carried out, and the method for determining its heat capacity over a wide range of temperatures, including at high values, was chosen. This is especially important for numerical studies to justify the safety of designed reactor installations with liquid metal coolants, such as BREST-OD-300 and BR-1200. Measuring the properties of lead at temperatures close to the boiling point is often difficult due to the lack of reliable methods and materials that can withstand temperatures above 2273 K. At present, theoretical approaches to calculating the properties of simple liquids based on phonon theory are being actively developed. Such approaches can be used to derive semiempirical relations for the heat capacity of liquid lead that would allow physically correct extrapolation of the data to the high-temperature region. In this regard, the aim of this work is to obtain a relationship for calculating the heat capacity of liquid lead from its melting point to its boiling point based on modern theoretical approaches. To achieve the set goal, the following tasks were solved. Firstly, an analysis of the works of various authors was carried out and empirical formulas were selected that make it possible to reliably calculate the heat capacity at a constant volume c_v (isochoric heat capacity) for a lead coolant from the melting point to 1500 K. Secondly, based on them, using phonon theory, an approximating formula was constructed, thanks to which it is possible to physically correctly extrapolate the properties of lead to the boiling point (2022 K).

An analysis is performed of the phosphate water chemistry of a high-pressure drum boiler. In Russia, water chemistries with purely phosphate alkalinity and phosphate-and-alkali water chemistry are now mainly used at power plants equipped with drum boilers. One of the main quantitative parameters determining the maintenance of phosphate water chemistries is the ratio of sodium and phosphate concentrations. Calculated dependences of the ratios of pH, the concentration of phosphate, and the sodium-to-phosphate concentration are given. A relationship is found between such ratios and the domains where acid–phosphate corrosion, the hydrogen embrittlement of metal, and alkali cracking occur. It is shown that at concentrations of phosphate below 2.5 mg/dm³, the chloride and sulfate concentrations in boiler water must be monitored to avoid the hydrogen embrittlement of metal. Dependences are presented for the pH and sodium-to-phosphate concentrations at different temperatures. Results are presented from industrial tests of purely phosphate alkalinity water chemistry during the startup and normal operation of a boiler. Analysis of the chemistry of a high-pressure drum boiler water shows that the concentration of phosphate in the pure compartment of a drum has almost no effect on the pH, but the concentration of phosphate in the drum’s salt compartment affects it strongly. Attention should therefore mainly be given to the pH prescribed by the relevant standard when managing the water chemistry in the pure compartment. It is shown that phosphate hideout is often observed when starting power units equipped with high-pressure boilers, so mono- and disodium phosphate solutions are used to maintain the pH and concentrations of phosphate. An analysis of the quality of boiler water during a startup shows there was a drop in the concentration of phosphate in the boiler water and a rise in the sodium-to-phosphate concentrations, so a hideout occurred. The possibility of identifying deviations when monitoring phosphate water chemistry is thus demonstrated, based on an analysis of sodium-to-phosphate ratios of concentrations.

Based on modern theoretical knowledge and the results of representative experimental studies, the phenomenology of reflooding of fuel assemblies is considered. The parameters (test section pressure, water subcooling, peak cladding temperature at the start of the flooding, bundle power, etc.) maintained in the experiments under consideration are close to those expected when implementing measures to manage hypothetical severe accidents at pressurized water reactors. A list of processes accompanying the reflood of fuel-rod assemblies has been formulated, and specific effects have been established that can lead to a change in the local conditions of heat exchange between the cladding of fuel-rod simulators and the steam-water mixture and affect their quenching. A comparison of the results of experimental studies showed the influence of cooling water flow rate on the spread of measured values of quench time in the upper part of the fuel assembly. The view of reflood physics allowed us to analyze the results of validation of the SOCRAT code in experiments of varying phenomenological complexity (in an intact core, with an intense steam-zirconium reaction, formation of a melt). The analysis showed that the SOCRAT code correctly predicts the temperature histories of the fuel-rod simulator claddings, the quench time, and the total mass of hydrogen released during the experiment with a tendency toward slight underestimation; the modeling results do not contradict the experimental data. During validation, it was established that the thermal hydraulics model makes the greatest contribution to the assessment of the model error in calculating the quench time and the total mass of hydrogen production when modeling experiments of varying phenomenological complexity. Good predictive capabilities of the SOCRAT code confirmed the applicability of a one-dimensional approach to modeling the reflooding of fuel assemblies.