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.

The current state and development trends of geothermal energy are discussed based on an analysis of the materials of the World Geothermal Congress (WGC-2020 + 1) held in Iceland as well as articles published after this event. Promising directions and scales of use of geothermal resources in power generation, heat supply, and other areas of the economy are shown. A constant increase in the number and total capacity (by 27% over 5 years) of geothermal power plants in the world is noted, and statistical data on countries for 2015 and 2020 are presented according to the total installed capacity of geothermal power plants (GeoPP), the level of annual production of geothermal electricity, and the expected installed capacity for 2025. The location of the main geothermal power plants on the world map in 2020 is shown. The levels are considered risk and the amount of funding required at various stages of the creation of geothermal power plants in new fields, where the cost of building a power plant is 30% of the total cost of a GeoPP with drilling and well development. An analysis of the presentations on the power industry indicates that there is still significant interest in the use of binary power plants for the utilization of geothermal heat. As promising, the developments of new technological solutions for improving binary power plants based on the optimization of the choice of the working fluid and for improving the reliability of geothermal steam turbine plants by superheating the flash steam due to the use of a hydrogen-oxygen steam generator are presented. There has been an increase in interest in obtaining "green" hydrogen based on environmentally friendly geothermal power generation. The possibility of hydrogen production using electrolyzers, which use excess electricity at the GeoPP during periods of daily unloading, is shown.

The development of the modern nuclear industry is characterized by the conversion of operating power units to operation at a thermal power level above the current rated power level to enhance generation of electricity and reduce its cost. This process is referred to as a power uprate (PU). This can be done by increasing the thermal power of a reactor units and improving the efficiency of the turbine unit. In Russia and abroad, the thermal power of NPP power units is usually increased by 2–20

With a growth in the scales on which binary cycle (ORC) power units are constructed, new technical solutions aimed at improving the efficiency of binary technologies are searched for. To this end, the possibility of using multistage ORCs based on the principle of incremental (staged) conversion of geothermal fluid energy is also studied. In view of the fact that low-temperature geothermal resources dominate around the world (the fluid outlet temperature is lower than 130°С in up to 60% of all geothermal fields), the optimization calculated studies of two- and three-stage ORCs were carried out for a source geothermal fluid with a temperature of 120°С. The article presents the results of studying the effect that the choice of low-boiling organic substances and the geothermal fluid temperature in the stages have on achieving the cycle maximal power output and minimal fluid mass flowrate. The technical characteristics of two- and three-stage ORCs are compared with those of a conventional single-loop ORC power unit in the case of using various nontoxic and fire- and explosion-safe organic substances. It is shown that, by applying a three-stage process circuit with R-600 working fluid in all loops and using geothermal fluid with a temperature of 120°С, it is possible to increase the amount of heat transferred to the binary cycle by 36.5% in comparison with the single-stage process circuit. In accordance with the previously performed calculations, the growth of heat transferred to the binary cycle in the case of using geothermal fluid with a temperature of 180°С amounted to 15.0%. It has been found that the minimal (net and gross) mass flowrates of geothermal fluid with a temperature of 120°С in the three-stage process circuit are achieved in the case of using R-600 substance as working fluid in the first, second, and third stages and make 44.6 and 42.7 (kg/s)/MW, respectively. The obtained results can be used in the development and designing of multistage ORCs with the geothermal fluid temperature equal to 120°С.

The creation of efficient technologies for converting low-temperature heat into electricity using binary power units operating on the organic Rankine cycle is an urgent problem of modern energy. Interest in these technologies is steadily growing since they make it possible to utilize the heat of waste heat carrier in various industries and geothermal power plants (GeoPPs). Currently, low-temperature resources, which are widespread throughout the world, are increasingly used as sources of geothermal heat carrier for generating electrical energy. One of the ways to increase the efficiency of binary technologies can be the use of multicascade binary energy complexes, which are several binary circuits connected in series. Due to the possibility of optimal selection of the working fluid in each circuit, the highest efficiency of an individual cascade and the energy complex as a whole is ensured. Preliminary estimates showed that the additional power that can be obtained by adding a new cascade decreases as the number of cascades increases. Optimization calculations were limited to comparing two- and three-stage binary power complexes with a single-stage binary power unit. The results of studies into the influence of the choice of an organic working fluid and the temperature of a geothermal heat carrier on the technical and economic characteristics of multicascade binary energy complexes with the utilization of a geothermal heat carrier with a temperature of 70°C are presented. It has been established that the efficiency of heat transfer to the binary cycle of multicascade energy complexes decreases with an increase in the temperature of the initial geothermal heat carrier. It is shown that the greatest decrease in the specific consumption of the geothermal heat carrier and the simultaneous increase in power during the transition from a single-stage power unit to two- and three-stage power complexes are achieved at low values of its temperature.

The desire to utilize waste heat from various industrial and technological processes leads to the search for new technical solutions and the development of technologies aimed at converting the thermal energy of low-grade heat carriers into electrical energy. Today, one of the most widespread technologies for generating electricity based on the use of low-grade heat is the organic Rankine cycle, which is implemented in binary cycle (ORC) power plants. The increased interest in these technologies is explained by the fact that significant initial capital costs for the creation of binary plants and their relatively low economic performance are in most cases offset by low operating costs for fuel. The use of multistage ORCs can become one of the ways to increase the efficiency of waste heat utilization. Specific examples and promising possibilities for the practical use of modular-staged ORCs in order to utilize the heat of waste heat carriers of various industries are presented. The features of multistage schemes are studied, the operation of which is based on the principle of incremental (step-by-step) energy conversion of a high-temperature geothermal single-phase water heat carrier in ORCs to increase the efficiency of using geothermal resources. Some results of computational studies of thermodynamic indicators and technical characteristics of two- and three-stage ORCs with a high-temperature (180°C) initial geothermal fluid are considered. The analysis of the technical characteristics of two- and three-stage ORCs is carried out in comparison with the traditional single-circuit ORC power unit when using various organic substances as a working fluid. It is shown that the use of a two-stage scheme makes it possible to increase the amount of heat transferred to a binary cycle by 15% in comparison with a single-stage scheme, and the use of a three-stage scheme by 18.9%. When implementing the developed methodology for numerical modeling of geothermal and binary circuits, it is possible to optimize the technological schemes of two- and three-stage ORCs according to the maximum installed power and minimum mass flowrate of the initial geothermal fluid.

The erosion–corrosion interaction of the metal of a working surface of a process loop with one- and two-phase flow of the coolant is considered from the standpoint of corrosion and mass transfer in conjunction with the water-chemistry regime. A classification of the mechanisms of metal thinning under the influence of the flow of the working medium is formulated taking into account the kinetics of their development in time, the main factors (erosion–corrosion parameters) are determined, and the computational codes used for predicting the rate of erosion–corrosion are noted. The features of the erosion–corrosion interaction of one- and two-phase flow with the metal in the working loop of a nuclear power plant are considered. The results of computational modeling of the erosion–corrosion of metal in a two-phase flow are presented. A kinetic-migration approach to determining the zones of the greatest local erosion–corrosion thinning of pipeline elements and equipment of NPP power units is proposed. It is shown that there is great utility in taking into account the effects of the erosion–corrosion interaction of one- and two-phase flows with metal in the R&D work on NPP power units.

One of the promising areas of applying hydrogen technologies in power engineering is to increase the capacity utilization factor and efficiency of turbine units by means of hydrogen–oxygen steam generators for superheating the working medium under the conditions in which the surplus electricity generated at power plants during the periods of daily and seasonal reduction in electric power consumption can be used for generating hydrogen. The use of steam superheating systems on the basis of hydrogen–oxygen steam generators at geothermal power plants is especially important in view of a low energy potential of geothermal heat carrier serving as the initial heat source. The article presents the results from computational studies of the technical advisability and technical-economic efficiency of implementing systems for increasing the secondary flash steam energy potential by using a hydrogen–oxygen steam generator and a binary power unit at a direct-cycle geothermal power plant operating on steam hydrotherms. The results from computational studies into the power characteristics of a combined binary cycle geothermal power plant with secondary flash steam superheating depending on the expansion pressure variations and the hydrogen–oxygen steam generator capacity are considered. It has been determined that the use of a 12-MW hydrogen–oxygen steam generator for superheating secondary flash steam results in that the steam wetness downstream of the steam turbine last stage decreases from 14 to 7%. Calculation results have shown that the topping of a direct-cycle geothermal power plant with a system for increasing the energy potential of secondary flash steam on the basis of a hydrogen–oxygen steam generator and a binary power plant makes it possible to increase the geothermal power plant capacity by almost 25% and its efficiency by 3.0–3.5%. Based on the feasibility study results, investors can select the optimal composition and characteristics of equipment in implementing a system for increasing the energy potential of secondary flash steam using a hydrogen–oxygen steam generator and a binary power unit at a direct-cycle geothermal power plant.

Basic principles are examined of the application of software tools (ST) for predicting the erosion-corrosion (EC) rate to ensure the integrity of equipment and piping of nuclear power station (NPS) power units. Methods for solving the erosion-corrosion problems encountered in NPS power units have been determined. Software tools that are used most widely throughout the world to solve erosion-corrosion problems in the nuclear power industry are reviewed. The specifics in the application abroad and in Russia are highlighted. Attention is given to the successful foreign experience in improving the corrosion-erosion resistance of piping and equipment based on the solution implemented in designing NPS power units. Information is presented on the development of Russian software tools and the results of their application to render the integrity of piping and equipment of NPS power units with a VVER reactor or fast breeder reactor due to numerical prediction and early detection of the maximum allowable erosion-corrosion metal thinning. The feasibility is substantiated of using the software tools in designing new NPS power units with a VVER-1200 reactor, assessing the residual service life, and prolonging the operation of existing NPSs. Examples are given of the ways for reduction in the erosion-corrosion rate of equipment components and piping of nuclear power units, for example, by controlling the intensity of the hydrodynamic component of erosion-corrosion and proper selection of the metal. It is demonstrated that the cost of power units with a VVER-1200 reactor (including export deliveries) can be reduced by a change-over to less erosion-corrosion resistant but relatively inexpensive steels. The prospects are noted on application in practice of STs to assess the carry over of iron-rich corrosion-erosion products into the working fluid of an NPS with a VVER-reactor. It is pointed out that, when changing over to operation of NPS power units at a super-rated power, this factor should be estimated using STs, and its effect on the wear rate and location of the zones wherein is the highest rate of thinning of the pipeline walls and equipment must be considered.

The article considers the specific features of and prospects for improving the efficiency of geothermal power plants (GeoPPs) that use a steam–water mixture from geothermal fields and steam superheating as an energy source. The process flow diagram of a combined binary-cycle GeoPP with two separation pressures and flashed steam superheating with the use of a hydrogen–oxygen steam generator is proposed. The advisability of using a separator downstream of the high-pressure section for decreasing the steam moisture at the turbine condenser inlet is substantiated. The article also presents the results from numerical optimization investigations of the effect that the choice of organic working fluid has on the efficiency, safety, and environmental characteristics of the binary installation used as part of a combined-cycle GeoPP. The following groups of organic substances as possible candidates for use as working fluid are considered: nontoxic, nonflammable, and nonexplosive ones (group I); low-toxic, nonflammable, and nonexplosive ones (group II); nontoxic inflammable ones (group III); and low-toxic, inflammable, and explosive ones (group IV). Typical dependences characterizing the effect that the pressure in the expander and the saturation pressure in the evaporator have on the binary turbine net power output, on the specific flowrate of separated geothermal brine per unit power capacity, on the binary cycle efficiency, and on the GeoPP efficiency as a whole are shown taking as examples the use of cyclobutane and octafluoropropane as a working fluid. For a few working fluids, the existence of extremes in the above-mentioned dependences is established, which determine the binary installation optimal power values and the minimal geothermal brine specific flowrate. Based on the numerical analysis results, limitations are imposed on the admissible maximum and minimum pressure values in the binary circuit. Bar charts of calculated process characteristics influencing the binary turbine flow path’s design and efficiency are plotted. A priority (according to the maximum net power output criterion) list of working fluids relating to the group of environmentally friendly organic substances for the combined-cycle GeoPP binary installation with flashed steam superheating taking into account process-related limitations is drawn up.

The article considers the specific features related to operation of the power valve and orifice lines within turbine plant piping systems whose inlets receive water medium with saturation parameters (separated moisture or condensate). It is shown that transportation of working medium in these piping systems is accompanied by pressure drop, boiling, and formation of various two-phase flow patterns from bubble in the initial segment to dispersed-annual in the end segment. Under certain conditions, a slug flow pattern can occur, which behaves as a source of piping vibration. Practical experience has shown that the use of homogenizing inserts for suppressing vibration load in the heating steam condensate (HSC) discharge lines downstream of the moisture separator reheaters (MSRs) of nuclear power plant (NPP) turbines often leads to intensified local flow-accelerated corrosion and pipeline failures. The article considers examples illustrating failures of piping segments downstream of homogenizing inserts and presents statistical data on damageability of heating steam and separated moisture piping of NPP turbines. The steam–water flow patterns in the MSR HSC transportation line of an NPP turbine are determined. The results from hydrodynamic modeling of working medium flow under the conditions of an abrupt expansion at the outlet from the homogenizing insert channel are presented. It is shown that the location of zones characterized by the maximum wear of piping downstream of homogenizing inserts in the MSR HSC discharge lines is determined by the flow pattern and specific features of the working medium flow hydrodynamics. It has been established that droplet impingement erosion is the dominating mechanism causing destruction of stainless-steel piping segments downstream of the homogenizing inserts in the MSR HSC lines of NPP turbines. It is important to note that, if the pipeline is made of carbon or low alloy steel, its metal experiences a combined effect of droplet impingement erosion and flow-accelerated corrosion. The obtained study results can be used in elaborating measures aimed to prevent wear of piping components in the heating steam condensate and separated moisture discharge lines of NPP turbines.