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Porous media have wide application in renewable energy conversion processes, such as solar-thermal fuels production and decarbonization. Heat transport mechanisms within porous media can be highly complex, particularly under extreme conditions encountered in concentrated solar thermal reactors in which direct measurement of temperature is challenging. Here, we implement and report an inverse heat conduction model to estimate the temperature distribution throughout a porous substrate domain in a direct solar methane pyrolysis process. By solving a two-dimensional heat transfer problem and applying an inverse optimization algorithm, we estimate the quasi-steady state spatial temperature distribution in a fibrous porous carbon substrate. The results are validated indirectly by experimentally measured graphite deposition and a simplified reaction kinetic model. [ABSTRACT FROM AUTHOR]

Yttrium hydride (YH x), celebrated for its exceptional thermal stability and capacity to maintain a considerable hydrogen content even at temperatures exceeding 1143 K, is a prime candidate for serving as a moderator in high-temperature reactions in thermal nuclear reactors. This research focuses on the fabrication of yttrium hydride monoliths from hydrogenated powder, using Spark Plasma Sintering (SPS) across a range of sintering conditions. A comprehensive examination was conducted to evaluate the morphology, distribution, size, and dehydrogenation properties of the YH 2 phase, the sub-hydrogen phase, and the precipitated yttrium within YH x monoliths fabricated via this approach. The findings elucidate the dehydrogenation mechanism of yttrium hydride during the SPS process, emphasizing the crucial role of hydrogen release. This release substantially influences the size and distribution of the yttrium precipitates and modifies the surface free energy of the YH x monoliths, which in turn influences the material's defects. Consequently, this process promotes the formation of pores along the grain boundaries, which may lead to the emergence of micro-cracks. These micro-cracks accelerate the release of hydrogen from the material. [Display omitted] • YH x synthesized via SPS achieve optimal density at 1000 °C with 65 MPa. • H/Y atomic ratio diminishes above 1000 °C, impacting hydrogen retention in YH x. • SPS parameters effectively control the grain size and morphology of YH x. • Dehydrogenation is associated with alterations in size and distribution of Y. [ABSTRACT FROM AUTHOR]

An increase in power during transient operating modes of reactors can lead to the depressurization of fuel rods due to the stress corrosion cracking mechanism. Expansion of fuel pellets due to increasing power induces tensile stresses in the cladding, which can initiate the formation and growth of corrosion cracks in the presence of aggressive fission products. Therefore, the plotted limit curve is primarily aimed at preventing circumferential stresses in the cladding from exceeding a certain maximum value during abrupt changes in power. The present article describes a system for performing multivariate statistical calculations of a single power increase to plot an envelope curve for the permissible area of fuel rod operation. The system uses the START-3A code to perform fuel rod calculations, which includes the ability to vary model and design parameters. The methodology for the calculated limit curve for a rapid increase in the power of a VVER-1200 reactor is presented with examples. [ABSTRACT FROM AUTHOR]

For the first time, a synergistic energy-efficient combination of microwave-xenon (MW-XE) irradiations in presence of photoactive ternary acidic deep eutectic solvents (TADES) has been applied for intensification of ethyl levulinate synthesis from delignified sugarcane bagasse (DSB) under mild (90 min, 90 °C) and environmentally benign process conditions. The Taguchi orthogonal designed optimized conditions (20 W/cm3 of MW specific irradiation power input, 1 mol/mol of FeCl3 to citric acid ratio, 90 min of reaction time, 150 W of XE specific power input) rendered maximum 61.3 mol% of EL yield (selectivity: 87.70 ± 0.5%). Remarkably, synergistic effect of MW and XE irradiation significantly enhanced the EL yield (61.3 mol%) compared to the individual MW (34.52 mol%) and XE (22.67 mol%) irradiation at otherwise optimized reaction conditions. Moreover, the MWXE irradiated reactor (MWXER) exhibited a significant 79.10% increase in EL yield compared to the conventional thermal reactor (CTR), at the expense of 10% less energy consumption. The ethyl levulinate could be recovered efficiently through green protocol from reaction mix resulting in high purity (97 ± 0.5%) and TADES was sustainably reused in the process. The optimally generated product EL when blended (5 and 10 vol.%) with B10 and B20 (10% and 20% biodiesel-diesel blend) could provide 21–31% reduction in HC and 7.3–36% reduction in CO in comparison with petro-diesel. It was also explored that, at similar optimal parametric combinations, the TADES produced 29.5% greater EL yield in comparison with the standard ionic liquid BMIMCl. The life cycle environmental impact analysis (LCEIA) of the overall process revealed that the 5 vol.% EL blending with B10 contributed lowest environmental impacts mitigating marine ecotoxicity, human toxicity, fossil depletion, and climate change by 77.9%, 77.4%, 78.4% and 77.5%, respectively. [ABSTRACT FROM AUTHOR]

ABSTRACT Prevention of thermal runaway and establishment of safe‐economic operating conditions are crucial for the practical operation of single diffusion‐controlled liquid–liquid reactions occurring in isoperibolic semibatch reactors. Hence, in this study, a mutual information‐based multiple feature recognition criterion (MI‐MFR) was innovatively proposed, for which the maximum relevance minimum redundancy approach was introduced in feature screening; in combination with the support vector machine algorithm, various thermal behaviors can be effectively recognized. On this basis, a series of boundary diagrams were established accordingly, the impact of the variation in model parameters on which was systematically explored. Subsequently, an improved generalized thermal safety region was developed by introducing the upper thresholds in normal and cooling failure scenarios. Meanwhile, the robustness and progressiveness of the established MI‐MFR criterion were confirmed by comparison with other conventional criteria. Finally, MI‐MFR‐based procedures were constructed to identify thermal behaviors and optimize safe‐economic operating conditions in practices, based on which the optimum operating conditions of toluene mononitration were obtained. [ABSTRACT FROM AUTHOR]

Nuclear microreactors are a potential technology to provide heat and electricity for remote microgrids. There is potential for the microgrid on the island of El Hierro to use a microreactor, within an integrated energy system (IES), to generate electricity and provide desalinated water. This work proposes a workflow for optimizing and analyzing IESs for microgrids. In this study, an IES incorporating a microreactor, thermal energy storage (TES) system, combined heat and power plant, and a thermal desalination plant was designed, optimized, and analyzed using Idaho National Laboratory's Framework for Optimization of Resources and Economics (FORCE) toolset. The optimization tool, Holistic Energy Resource Optimization Network (HERON), was used to determine the optimal capacity sizes and dispatch for the reactor and thermal energy storage systems to meet demand. The optimized reactor and TES sizes were found to be 11.61 MWth and 58.47 MWhth, respectively, when optimizing the IES to replace 95% of the island's existing diesel generation needs. A dynamic model of the system was created in the Modelica language, using models from the HYBRID repository, to analyze and verify the dispatch from the optimizer. The dynamic model was able to meet the ramp rates while maintaining reactor power with minimal control adjustments. [ABSTRACT FROM AUTHOR]

The CONUS+ experiment aims to detect coherent elastic neutrino-nucleus scattering (CE ν NS) of reactor antineutrinos on germanium nuclei in the fully coherent regime, continuing on this way the CONUS physics program started at the Brokdorf nuclear power plant, Germany. The CONUS+ setup is installed in the nuclear power plant in Leibstadt, Switzerland, at a distance of 20.7 m from the 3.6 GW thermal power reactor core. The CE ν NS signature will be measured with the same four point-contact high-purity germanium (HPGe) detectors produced for the former experiment, however refurbished and with optimized low energy thresholds of about 160 eV ee . To suppress the background in the CONUS+ detectors, the passive and active layers of the original CONUS shield were modified such to fit better to the significantly changed background conditions at the new experimental location. New data acquisition and monitoring systems were developed. A direct network connection between the experiment and the Max-Planck-Institut für Kernphysik (MPIK) makes it possible to control and monitor data acquisition in real time. The impact of all these modifications is discussed with particular emphasis on the resulting CE ν NS signal prediction for the first data collection phase of CONUS+. Prospects of the planned upgrade in a second phase integrating new larger HPGe detectors are also discussed. [ABSTRACT FROM AUTHOR]

In this study, we present on-the-fly thermal expansion methodology for direct Monte Carlo coupled multi-physics reactor simulations. This approach allows the problem geometry to be thermally expanded on-the-fly during particle tracking using local temperatures, such as pin-averaged temperatures, obtained from the thermal-hydraulics solver. Numerical experiments demonstrated that modeling thermal expansion with local temperatures for thermal expansion improves the accuracy of reactor simulations, both for reactor eigenvalue and pin powers, compared to using global core-averaged temperatures. Additionally, the use of thermal expansion also improves the isothermal temperature coefficients, making them approximately 0.77 pcm/K closer to the measured data. Finally, results for depletion problems showed that incorporating thermal expansion in direct reactor modeling enhances the predicted critical boron concentration, particularly at high power and higher fuel burnup. These findings suggest that including thermal expansion in reactor modeling is essential for improving the fidelity of simulations. [ABSTRACT FROM AUTHOR]

Nuclear reactivity and neutron population density are critical parameters for quantifying and describing the behavior of a nuclear reactor. Accurate knowledge of reactivity is essential for the safe control and operation of a reactor. Various approaches and methods for calculating reactivity are reported in the literature. In this paper, we propose using the Euler-Maclaurin formula to numerically solve reactivity through the inverse point kinetics equation, a key model in the design of digital reactivity meters. By approximating an integral as a sum in the expansion of a continuous integral into a discrete version, and considering only the first three Bernoulli numbers while reducing higher-order derivatives, we derive a model to calculate nuclear reactivity as a function of neutron population density and physical constants in thermal reactors using uranium as nuclear fuel. [ABSTRACT FROM AUTHOR]

Metal hydride (MH) suffers from strong thermal effects during hydrogen absorption. To fully utilize the reaction heat during hydrogen absorption, phase change material (PCM) can be used to achieve efficient thermal management in the reactor. A novel MH-PCM reactor with the partition arrangement of MH and PCM was proposed in this paper. Then, the two-dimensional multiphysics coupled model of the reactor was developed, and the effects of the number of partitions n , the mass of PCM and the hydrogen absorption pressure P a on the hydrogen absorption performance were discussed detailedly. The results indicated that the novel MH-PCM reactor not only increases the heat transfer area and boots the hydrogen absorption rate, but also improves the uniformity of temperature distribution. As the n increases from 2 to 5, the hydrogen absorption time gradually shortens. Compared to the conventional MH-PCM reactor, the time for 90% hydrogen absorption shortens by 67.13%. Furthermore, the hydrogen absorption rate can be enhanced with the increasing mass of PCM and P a. However, the larger these values are, the weaker the enhancement effect becomes. The results of this paper may provide a new direction for the optimized design and engineering application of MH-PCM reactors. • A novel reactor with the partition arrangement of MH and PCM is proposed. • Effects of partition number, hydrogen storage pressure and PCM mass are examined. • Novel reactor boosts hydrogen absorption rate and improves temperature uniformity. • The hydrogen absorption time is shortened by 67.13% via a partition number of 5. • Absorption enhancement ratio reduces as hydrogen pressure and PCM mass increase. [ABSTRACT FROM AUTHOR]

The investigation of critical flow model for supercritical pressure condition is relatively rare. Based on isentropic flow and thermal equilibrium assumptions, a model is derived to calculate discharge flow rate and critical pressure. Considering the influence of friction and local resistance, a correction coefficient is added which can be calculated from CFX analysis software. The model avoids the calculation of quality and is applicable to wide range which covering the subcooled water, two-phase mixture, steam critical flow under subcritical pressure and supercritical pressure. Reasonable agreement is shown between model predicted results and experiment data, illustrating the accuracy of the proposed model. [ABSTRACT FROM AUTHOR]

Zirconium hydride is commonly used for next-generation reactor designs due to its excellent hydrogen retention capacity at temperatures below 1000 K. These types of reactors operate at thermal neutron energies and require accurate representation of thermal scattering laws (TSLs) to optimize moderator performance and evaluate the safety indicators for reactor design. In this work, we present an atomic-scale representation of sub-stoichiometric ZrH2−x (0.3 ≤ x ≤ 0.6) , which relies on ab initio molecular dynamics (AIMD) in tandem with velocity auto-correlation (VAC) analysis to generate phonon density of states (DOS) for TSL development. The novel NJOY+NCrystal tool, developed by the European Spallation Source community, was utilized to generate the TSL formulations in the A Compact ENDF (ACE) format for its utility in neutron transport software. First, stoichiometric zirconium hydride cross sections were benchmarked with experiments. Then sub-stoichiometric zirconium hydride TSLs were developed. Significant deviations were observed between the new δ -phase ZrH2−x TSLs and the TSLs in the current ENDF release. It was also observed that varying the hydrogen vacancy defect concentration and sites did not cause as significant a change in the TSLs (e.g., ZrH1.4 vs. ZrH1.7) as was caused by the lattice transformation from ϵ - to δ -phase. [ABSTRACT FROM AUTHOR]

Several preliminary conceptual designs of nuclear thermal rocket reactor cores are presented that use tin-bonded monolithic ceramic [mononitride (UN), monocarbide (UC), and uranium dioxide (UO2)] fuel plates or pins with molybdenum-tungsten alloy clad. Neutron moderation is provided by a block of Be metal or composite materials using metal hydrides such as ZrH1.6 or YH1.6 with different matrices (MgO or Be). Mainly high-assay low-enriched uranium is considered, but highly enriched uranium is also assessed for a few configurations. Nominal core thermal power is 300 MW corresponding to about 66 kN (15 klbf) of thrust, and with minimal modifications, 500 MW may be possible (25 klbf of thrust). Depending on the configurations, the amount of 235U needed for criticality is 30 to 90 kg, and reactor weight is 2.5 to 3.8 tonnes. [ABSTRACT FROM AUTHOR]

The main advantages of ceramic materials are their excellent thermal, chemical, and mechanical properties. They also have a much lower density than metals, making them ideal for lightweight construction, which can also be interesting for space components. However, ceramics have not been widely used due to their low ductility and the challenges of mechanical processing using conventional methods like milling and turning. Additionally, integrating different functions into a single component has been limited. The introduction of additive manufacturing (AM) technologies has revolutionized this field. It is now possible to manufacture highly complex ceramic components with unprecedented functionality. By hybridizing different manufacturing technologies and materials, additional functions such as electrical contacts, sensors, and actuators can be directly integrated, leading to improved manufacturing costs and component properties. Three different demonstrator examples are presented in this paper to give a first impression of what will be possible in the field of space applications in the future. These examples are a ceramic igniter, a ceramic reactor for thermal decomposition of H 2 O 2 , and a ceramic aerospike engine. • Additive manufacturing of ceramic components allows geometrical functionalization. • Adding of further materials to AM components allows further functionalization. • Sequential & simultaneous manufacturing available for AM of multi-material component. • Hybridization of AM technologies allows optimization of component's quality and costs. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is a promising waste to energy technology for conversion of organic wastes with high water contents. There have been relatively few studies focused on evaluating the HTC of solid waste (SW). The studies have provided valuable information regarding HTC feasibility and potential environmental benefits. However, they lack the data necessary to understand how carbonization product composition and reaction extent change with the variation of operating parameter. This study sought to characterize kitchen waste from a university restaurant, to assess the impact of operating parameters on hydro-char and evaluate its potential as a solid fuel. The methodology for characterization was based on proximate analysis, ultimate analysis and calorific value. A ratio of dry sample to water of 1:9 was used to make a wet sample and stirred at 180 rpm in a thermal reactor under controlled HTC conditions. The results from proximate analysis revealed that moisture content, volatile matter, ash content and fixed carbon content were 9.6%, 65.1%, 13.6%, and 11.9% respectively. The ultimate analysis showed that carbon, hydrogen, nitrogen, Sulphur and oxygen were 48.8, 0.5, 0.4, 0.5 and 45.3% respectively. Mass yield of hydro-char decreased for all samples with increasing HTC reaction temperature. ANOVA confirmed the adequacy of the model, yielding R2 and adjusted R2 values of 0.8630 and 0.7398, respectively with a P value of 0.003 and F-value of 7.00. The high heating value, ultimate analysis and proximate analysis suggested that the hydro char from kitchen waste can potentially be utilized as a solid fuel. [ABSTRACT FROM AUTHOR]

Turbulent mixing within sub‐channels plays a crucial role in understanding the thermal hydraulics of reactor channels. It serves as an empirical parameter in sub‐channel analysis and has long been a challenge in the nuclear industry. Conducting experiments in this context is challenging due to the stringent requirement of maintaining pressure balance among sub‐channels to prevent convection effects. Fortunately, direct numerical simulation (DNS) is emerging as an invaluable tool for addressing this persistent issue. DNS enables the direct computation of turbulent mixing by analyzing fluctuating lateral velocities, offering a more profound understanding of the underlying phenomena. In this study, DNS was conducted at six Reynolds numbers ranging from 17,640 to 1.5 × 105 in pressurized water reactor (PWR) geometry to investigate the lateral mixing driven by turbulence. By studying intricate mechanisms governing the turbulent mixing, the valuable insights into reactor thermal performance and safety are provided. Furthermore, a correlation for turbulent mixing of energy based on the DNS data has been derived, enhancing our ability to model and predict this critical aspect of reactor behaviour. Additionally, this paper explores temperature fluctuations occurring at the fuel rod surface due to turbulence. A probabilistic distribution for temperature fluctuation under specific reactor conditions is presented. [ABSTRACT FROM AUTHOR]

The dissociation of the hydrogen molecule is rarely explored in the high-temperature flow of modern and historic nuclear thermal propulsion (NTP) engines. This study investigates the impact of absorption on highly-enriched and low-enriched uranium NTP reactors due to hydrogen dissociation surface reactions. Results show that with increasing temperature, dissociated hydrogen has a decreasing wall coverage but a significant crossflow velocity, as high as 81 mm/s, near the outlet due to absorption. This absorption changes the turbulent velocity profile while only having a small effect on the local Stanton number. Changing velocity profiles and mass loss to the wall can change mass flow rates, altering engine performance. Calculation and modeling via analytical solutions are unlikely as similar studies show non-uniqueness and existence issues at this study's R e w = 1.43. Follow-on computational fluid dynamic modeling is needed to fully capture the performance changes to the NTP engine. [Display omitted] • Notable hydrogen absorption into cladding begins at surface temperatures of 1500 K. • Highest temperatures cause the highest hydrogen absorption velocity near 81 mm/s. • Comparison to similar data shows the local Stanton Number is not largely impacted. • Axial increase in temperature may cause thermal gradients and flow circulation. • Others show R e w = 1.43 has multiple solutions and potential backflow at the wall. [ABSTRACT FROM AUTHOR]

The increasing installment of solar and wind renewable energy systems create a volatile energy demand to be met by electricity providers. A nuclear hybrid energy system is a nuclear reactor with energy storage that integrates into the grid with renewable energy sources. The Natrium design by TerraPower and GE Hitachi is a sodium fast reactor with molten salt energy storage. The Natrium design operates at steady state of 345 MWe and can boost up to 500 MWe for 5.5 hours. This study uses Dymola and the Modelica language to model the Natrium‐based nuclear‐renewable hybrid energy system. The dynamic system model is tested using hourly historical data from the state of Texas 2021 to show how renewables affect the electricity demand and how energy storage affects the Natrium system response to the demand. According to the results, while the available storage will allow the Natrium design to boost electricity production when the demand and electricity price is high making it more economically viable, the current molten salt storage is slightly undersized for the ERCOT market. [ABSTRACT FROM AUTHOR]

Ventilation air methane (VAM) from coal mining is a low-grade energy source that can be used in combustion systems to tackle the energy crisis. This work presents a numerical analysis of the thermal and stabilization performance of a VAM-fueled thermal reversal reactor with three fixed beds. The effects of the combustion chamber/regenerator height ratio (β), heat storage materials, and porosity on the oxidation characteristics are evaluated in detail. It is shown that the regenerator temperature tends to vary monotonically with β due to the coupling effect of the gas residence time and heat transfer intensity. The optimal β is determined to be 4/6, above which the system may destabilize. Furthermore, it is found that regardless of the methane volume fraction, the regenerator with mullite inserted has the highest temperature among the heat storage materials investigated. In contrast, the temperature gradually decreases and the system becomes unstable as SiC is adopted, signifying the importance of choosing proper thermal diffusivity. Further analysis reveals that the porosity of the heat storage materials has little effect on the system stability. Decreasing the porosity can effectively reduce the oscillation amplitude of the regenerator temperature, but it also results in greater pressure losses. [ABSTRACT FROM AUTHOR]

A practical carbon dioxide (CO2) conversion and utilization system shows great potential for ameliorating the greenhouse effect. Herein, an integrated carbon aerogel-based photothermal catalysis microreactor with photothermal conversion, enhanced mass transfer adsorption and a thermal catalytic reactor is designed. As a solar-powered CO2 utilization module, this microreactor can conveniently convert CO2 into economically valuable products without elaborate equipment and operation processes. [ABSTRACT FROM AUTHOR]

In this paper, a solar thermochemical reactor is designed based on a 5 kW non-coaxial concentrating solar simulator, and a mathematical model is established for thermal calculations. The calculated temperature distribution is used as a load condition for thermal stress analyses. The model is used to study the influence of the solar simulator power, solar reactor inner wall material's emissivity, working pressure, gas inlet velocity, and thermocouple opening diameter on the thermal stress of the solar reactor. The results show that thermal stress increases with the increase in solar simulator power and the emissivity of the inner wall material in the solar reactor. The inlet velocity and working pressure have little effect on the thermal stress of the reactor and cannot prevent damage to the reactor. In the case of maintaining the diameter of the thermocouple at the front end of the reactor, increasing the diameter of the thermocouple inside the reactor leads to an increase in thermal stress around the reactor. Meanwhile, using a finer thermocouple can reduce the thermal stress inside the reactor and extend its service life, which will provide a foundation for designing practical industrial applications in the future. [ABSTRACT FROM AUTHOR]

Recently, thermodynamic modeling has demonstrated that reduction of nonstoichiometric oxides in a counterflow gas current with a single inlet and exit must result in an equilibrium temperature gradient that deviates from the typically assumed isothermal operation at every single point but one, under assumed mass balance constraints. This necessity for a temperature gradient results in real processes that are near isothermal to deviate from the ideal reversible process, except for the single point where the Gibbs free energy change is zero. In this paper, new configurations with additional inlets and exits that can better approximate reversible and isothermal countercurrent flow reactors are considered and thermodynamically modeled. We show that it is possible to decrease irreversibilities while operating under the same maximum temperature, gas flowrates and initial nonstoichiometry simply by employing two or more exits and/or inlets. Under the most optimal conditions where the normalized irreversibilities are lowest, utilizing either an extra exit or extra inlet and exit show improved results in terms of minimizing the Gibbs free energy and lowering the needed separation work for the gases. Generally, as more irreversibilities are generated within the reactor, the more significant the usage of extra inlets/exits becomes. • Development of thermodynamic models for two new thermal reduction reactor configurations. • Gibbs free energy and separation work are examined to compare the different reactors. • Parametric study based on operating temperature, initial oxidized nonstoichiometry, and inlet sweep gas purity. • Both new reactor designs demonstrate a decrease in irreversibilities compared to the conventional design. [Display omitted] [ABSTRACT FROM AUTHOR]

While reactor wall preconditioning was previously shown to influence the yield in chemical vapor deposition (CVD), especially for the growth of carbon nanotubes (CNTs), it was limited to studying accumulating carbonaceous deposits over a number of runs. However, the effects of temperature and duration as the reactor walls are exposed to hot humidity for extended periods between growth runs were not previously studied systematically. Here, we combine experimental measurements with a mathematical model to elucidate how the thermochemical history of reactor walls impacts growth yield, especially knowing that only a specific range of humidity promotes growth. Importantly, we demonstrate a one-order-of-magnitude higher CNT yield by increasing the interim, i.e., the time between runs. We explain the results based on previously unexplored process sensitivity to trace amounts of oxygen-containing species in the reactor. In particular, we model the effect of small amounts of water vapor being desorbed from reactor walls during growth. Our results reveal the outgassing dynamics and show the underlying mechanism of generating growth-promoting molecules. By installing a humidity sensor in our custom-designed multizone rapid thermal CVD reactor, we are able to uniquely correlate the amount of moisture within the reactor to real-time measurements of growth kinetics, as well as ex situ characterization of CNT alignment and atomic defects. Our findings enable a scientifically grounded approach toward both boosting growth yield and improving its consistency by reducing run-to-run variations. Accordingly, engineered dynamics recipes with added preprocessing steps can be envisioned to leverage this phenomenon for improving manufacturing process scalability and robustness. [ABSTRACT FROM AUTHOR]

Thermal energy storage using coupled metal hydride reactors is attractive because it offers several advantages such as one-time hydrogen loading, high thermal storage density, compactness and possibility of simultaneous heating and cooling. This study presents experimental investigations on a coupled metal hydride based thermal energy storage system. Based on compatibility criteria of hydrides described in this work, LaNi 4.25 Al 0.75 for thermal energy storage and La 0.75 Ce 0.25 Ni 5 for hydrogen storage were chosen. The study employed two novel cartridge type coupled reactors with enhanced heat transfer surfaces. The effects of heat source and ambient temperatures on the system performance were investigated. The study reveals that coupled hydride systems with suitable pairs of hydrides can deliver high energy storage capacities at good thermal efficiencies. The heat output of 227.7 kJ was achieved with a heat transfer rate of 130.7 W at 55.7 % efficiency. The hydrogen storage alloy exhibited good compatibility with the energy storage alloy with fast hydrogenation and dehydrogenation. It also produced a cooling effect of 171.8 kJ while desorbing hydrogen. • Coupled LaNi 4.25 Al 0.75 -La 0.75 Ce 0.25 Ni 5 reactors for thermal storage were experimentally studied. • A procedure to determine the optimum initial state of coupled hydrides is provided. • Energy density of 135.14 kJ. kg MH - 1 at an average heat transfer rate of 130.7 W was achieved. • In addition to hydrogen storage, La 0.75 Ce 0.25 Ni 5 produced a cooling effect of 102 kJ. kg MH - 1 . • Effects of charging and discharging temperatures on thermal performance are investigated. [ABSTRACT FROM AUTHOR]

In situ X‐ray scattering provides valuable insights into the mechanisms and kinetics of reactions and structural transformations. For reactions and structural transformations primarily driven by temperature, and not coupled to chemical/electrochemical triggers, our ability to initiate and quench processes thermally is a practical limit for probing fast reactive phenomena. Meaningful quantitative analysis requires the dynamic phenomena to be triggered on fast time scales relative to the reaction/transformation kinetics. This article describes a new sample furnace, the Rapid‐Actuating Pneumatic Thermal Reactor or RAPTR, for time‐resolved in situ X‐ray scattering studies initiated by temperature. The RAPTR quickly heats and cools samples by translating them into and out of a pre‐heated hot zone. Using diffraction thermometry, it is shown that the samples can be heated/cooled in 10 s or less, with temperatures up to ∼1000°C being accessible. The application of the RAPTR furnace is demonstrated by exploring a fast solid‐state reaction: the synthesis of scheelite‐type lead tungstate, PbWO4, from PbO and WO3 for which Pb3WO6 is identified as a previously unrecognized reaction intermediate. [ABSTRACT FROM AUTHOR]

A sulfur recovery process is one of the most important processes in the oil and gas industry to get rid of hydrogen sulfide (H2S) which is produced from the acid gas removal process of sour natural gas to convert it into sweet natural gas. Actual data from a gas field is used to obtain a realistic comparison between two sulfur recovery techniques, through which researchers and/or manufacturers can obtain information that will help them choose the most appropriate and cheapest method. A total feed acid gas flow rate of 5.1844 MMSCFD with an H2S concentration of 24.62% by mole percent was produced from amine acid gas removal units. Claus sulfur recovery technique is a traditional chemical process that uses thermal and catalytic reactors. Therefore, an acid gas enrichment unit is applied to increase the H2S concentration to approximately 50% mole to provide reliable and flexible operation in the thermal and catalytic reactors. Moreover, a tail gas treatment unit is applied to increase the overall conversion efficiency to 99.90% with the Claus technique instead of 95.08% without it to achieve high sulfur recovery and reliable operation through the conversion of carbonyl sulfide (COS) and mercaptans. Studies on the safety and simplicity of the Claus technique revealed many important hazards and a large number of transmitters (379) and control loops (128) in one Claus train. THIOPAQ sulfur recovery as a new technology is a biological desulfurization process that uses a natural mixture of sulfide-oxidizing bacteria. It is also a unique H2S removal process with an efficiency of 99.999%. In addition, studies on the safety and simplicity of the THIOPAQ technique have shown that the hazards, the number of transmitters (74), and the number of control loops (29) of a one THIOPAQ train are lower. The THIOPAQ technique showed higher efficiency, was safer, simpler, and had lower CAPEX and OPEX. This study was conducted using Aspen HYSYS V11 and actual data. [ABSTRACT FROM AUTHOR]

Possible input data of a NPP power unit model for matching model states with prototype states are considered. The most important parameter used to match the states is the thermal power of the reactor unit (RU). Methods for accurate setting of the reactor plant power in the model were examined, namely, by using an automatic power controller (APC) and a mathematical boron controller. As part of matching the state of the nuclear power plant model with the prototype, a numerical experiment was carried out using PROSTOR, a full-scale simulation facility. The experiment was intended to obtain stationary states of the model with power in a range from 94% to 104% with a step of 0.05%. For modeling, the data pertaining to load 3 of unit 4 of the Kalinin NPP on the 248th effective day were used. In analyzing the results of a numerical experiment, two effects were discovered. One of them, exhibited in the derivative of the resulting plot of the dependence of pressure in the steam generator on power, is associated with reaching the upper limit of the capacity to control the pressure in the main steam collector (MSC). The control element of the pressure controller in the MSC is the control valves on the turbogenerator. At the moment that corresponds to the kink on the plot, they fully open, owing to which pressure control is no longer possible. The pressure in the MSC begins to rise. This effect corresponds to real processes occurring at nuclear power plants. In this case, it is proposed to use as one of the parameters of the model settings an adaptive coefficient to the concentration of boric acid in the reactor and control it by means of a mathematical boron controller. The second effect is that the pressure in the reactor cannot be accurately controlled because of the operating characteristics of the automation of tubular heating elements of the pressure balance (THE PB). In relation to this, it is proposed to use an additional mathematical controller of THE PB to match the state of the model with the prototype. These controllers have been successfully tested as part of the PROSTOR software package for matching the power of the reactor unit and the prototype. [ABSTRACT FROM AUTHOR]

Liquid organic hydrogen carriers (LOHCs) are considered a promising hydrogen storage technology. Heat must be exchanged with an external medium, such as a heat transfer fluid, for the required chemical reactions to occur. Batch reactors are simple but useful solutions for small-scale storage applications, which can be modelled with a lumped-parameter approach, adequately reproducing their dynamic performance. For such reactors, power is consumed to circulate the external heat transfer fluid and stir the organic liquid inside the reactor, and heat transfer performance and power consumption are two key parameters in reactor optimisation. Therefore, with reference to the hydrogen release phase, this paper describes a procedure to optimise the reactor thermal design, based on a lumped-parameter model, in terms of heat transfer performance and minimum power consumption. Two batch reactors are analysed: a conventional jacketed reactor with agitation nozzles and a half-pipe coil reactor. Heat transfer performance is evaluated by introducing a newly defined dimensionless parameter, the Heat Transfer Ratio (HTR), whose value directly correlates to the heat rate required by the carrier's dehydrogenation reaction. The resulting model is a valid tool for adequately reproducing the hydrogen storage behaviour within dynamic models of complex and detailed energy systems. • Thermal design of hydrogen storage systems based on LOHC batch reactors is analysed • Design is optimised to ensure effective heat transfer and minimum power consumption • Novel dimensionless parameter (Heat Transfer Ratio, HTR) is introduced • A threshold HTR value is identified, above which only marginal gains are achieved • The lumped-parameter model can be deployed in complex energy system dynamic models [ABSTRACT FROM AUTHOR]

The present study is focussed on the design and development of a single stage metal hydride hydrogen compressor. A 0.5 kg alloy mass capacity reactor is designed to withstand 100 bar at 120 °C. The Von Misses equivalent stress is calculated for the designed reactor and it is found to have a design margin of 11.4%. The reactor has an excellent weight ratio of 2.22. To enhance the thermal performance of the reactor, extended surfaces are incorporated. A numerical model is developed to compare the performance of three different fin configurations namely longitudinal fins, transverse fins and spiral fins. Longitudinal fins are found to provide better thermal enhancement during initial period of absorption half cycle. However, transverse fins showed better performance in the desorption case. Nevertheless, as the time progresses all the fin configurations showed similar performance under different operating temperatures. Further, hydrogen discharge rate is studied at various discharge pressure to understand the requirements while coupling with an empty cylinder or fuel cell. The study revealed that a 0.5 kg reactor can discharge hydrogen at the rate of 2.27 lpm for 2000 s when discharged to fill a cylinder up to 10 bar. The compression rate of the developed compressor is found to be 136 l/h at 10 bar discharge pressure and 373 K heat source temperature. The isentropic efficiency of the compressor is found to be 11.5%. [Display omitted] • Design methodology for single stage MHHC is presented. • Designed the reactor based on Von Misses equivalent stress. • Numerical model is developed using COMSOL Multiphysics. • Spiral, longitudinal and transverse finned MH reactors are extensively studied. • Performance study on the developed single-stage compressor is carried out. [ABSTRACT FROM AUTHOR]

The limited amount of economically suitable natural uranium resources forces us to improve the existing structure of the nuclear power system and its fuel cycle. With the current natural uranium reserves, it becomes practically impossible to significantly increase nuclear power plant (NPP) capacities in the existing system on the basis of thermal reactors operating in the open nuclear fuel cycle (ONFC). In order to solve this problem, the article considers the introduction of fusion-fission reactors (FFRs). FFR blankets produce 233U, which is further utilized in thermal reactors. In this article, fuel compositions of VVER-1200 reactors with the addition of 233U and thorium are studied, which make it possible to reduce the consumption of natural uranium and/or utilize already available raw materials in the form of depleted and regenerated uranium. On the basis of the scenario of the Russian nuclear power system (NPS) development within the ONFC with VVER-1200 reactors, the required 233U production volumes and the corresponding FFR fraction are determined for all fuel options. The risks of thorium introduction into the nuclear fuel cycle (NFC) are reviewed. [ABSTRACT FROM AUTHOR]

Readings of background cores of self-powered neutron detectors (SPND) are analyzed. A new method for independent evaluation of reactor thermal power is proposed. [ABSTRACT FROM AUTHOR]

A reactor is an important piece of equipment used for reactive power compensation in power system and has a significant impact on the safe operation of power system. Thermal behavior is one of the main causes of reactor failures. For an accurate analysis of the thermal behavior of reactors, electromagnetic–thermal–fluid multi-physics coupling modeling is chosen. However, there is a huge difference in size between the overall structure of the reactor and its insulating material, which makes it difficult to perform mesh generation, resulting in dense mesh and significantly increased solution degrees of freedom, thus making the solution of the reactor's multi-physics field model very time-consuming. To address this, this paper proposes a simplified processing method to accelerate the solution calculation of the reactor's multi-physics model. This method calculates the equivalent turns of each encapsulate with parallel coils in the reactor, simplifying the encapsulate into a single-layer coil, thereby greatly reducing the division and solution degrees of freedom of the multi-physics model, and thus accelerating the simulation calculation. Taking a BKDCKL-20000/35 dry-type air-core shunt reactor as an example, the outer diameter of the coil is nearly 12,000 times bigger than the coil insulation, which is a huge size difference. Both refined models and simplified models are established. Compared to the simulation results of the detailed model, the simplified model demonstrates good accuracy; the maximum relative error of temperature is just 2.19%. Meanwhile, the computational time of the simplified model is reduced by 35.7%, which shows promising effectiveness and significant potential for applying the optimization design and operation prediction of dry-type air-core shunt reactors for enhanced thermal performance. [ABSTRACT FROM AUTHOR]

The analysis of electro-magnetohydrodynamic (EMHD) has great importance due to its several functions such as fluid pumping, flow regulation in fluidics systems, thermal reactors, chromatography, micro coolers and fluid stirring. Based on above applications of EMHD, the consequences of electromagnetic induction on the ternary nanofluid (TNF) flow comprised of motile microbes over a Riga plate are observed. Additionally, the THF flow is subjected to the influence of uniform heat source, thermophoretic effect, activation energy, multiple slip conditions and Arrhenius activation energy. The TNF is made by the scattering of Al2O3, TiO2 and SiO2 nanoparticles in the base fluid, ethylene glycol (50%–C2H6O2) and water (50%–H2O). The phenomena have been formulated in the form of the system of PDEs, which are simplified to the dimensionless nonlinear system of ODEs by applying similarity substitutions. The solution of the obtained set of a differential equation is derived through the MATLAB package. It has been detected that the ternary hybrid nanofluid velocity significantly lessens with the varying numbers of ternary nanoparticles, while augments with the upshot of the Hartmann number. Furthermore, the influence of ternary nanoparticles drops, while the heat sink constant effect elevates the energy curve. [ABSTRACT FROM AUTHOR]

In the future, advanced reactors are expected to play an important role in nuclear power. However, their development and deployment are hindered by the absence of reliable and efficient models for analysis of system thermal hydraulics (TH). For instance, mixing and thermal stratification in reactor enclosures cannot be captured by traditional one-dimensional system codes, yet usage of high-resolution solvers is computationally expensive. Recent developments of coarse grid (CG) and system codes with three-dimensional capabilities have shown that they are promising tools for system-level analysis. However, these codes feature large turbulence model form and discretization errors and require further improvements to capture turbulent effects during complex transients. Improvements can be achieved by using data-driven (DD) approaches. This paper provides an overview of recent applications of DD methods in the areas of fluid dynamics and TH. It is demonstrated that they are being widely applied for engineering-scale analysis (e.g., closures for large eddy simulations/Reynolds-averaged Navier-Stokes using direct numerical simulation data). However, they cannot be directly employed for the system scale because of some features of the latter: usage of CG, transient nature of the considered phenomena, nonlinear interaction of multiple closures, etc. At the same time, accumulated experience allows outlining of potential frameworks for further developments in DD CG modeling of system-level TH. [ABSTRACT FROM AUTHOR]

The present investigation pertains to a theoretical study of mathematical model for methane steam reforming in membrane reactor, by simulating the operating variables of the reactor for high hydrogen yield and methane conversion. Basically, it deals with the development of the mathematical model of a fluidized bed Auto thermal membrane reactor (without integrated O2 perm-selective membranes), by using the mass balance macroscopically. Model is validated with the available experimental data in the literature and was found that the prediction from the models is in excellent agreement with the experimental values, with a maximum deviation of –12 to +13% and –12 to +1.8% for methane gas conversion and hydrogen yield, respectively. Finally, it investigates the effect of operating variables namely, reactor pressure, temperature, and steam to methane ratio (SMR) and permeates side pressure, on the methane gas conversion and hydrogen. The prediction reveals that the hydrogen yield and methane conversion increases with increase in reactor temperature and pressure whereas decreases with increase in SMR and permeate side pressure. [ABSTRACT FROM AUTHOR]

Methane sorption enhanced reforming (SER) is investigated in this work as a promising route for blue H 2 production. A 1-D dynamic heterogeneous model is developed to evaluate the thermal behavior of a fixed bed reactor under adiabatic conditions. The heterogeneous model allows to decouple the feed gas temperature from the initial solid one in order to investigate the behavior of the reforming step in a temperature swing reforming/regeneration process. The effects of the feed gas temperature, the initial bed temperature, and the bed thermal capacity are studied by evaluating the global impact of each parameter through a set of key performance indices (CH 4 conversion, H 2 yield and purity, carbon capture ratio) calculated as integrals over the duration of the reforming step. The results highlight the minor effect of the initial bed temperature on the process performances showing the potential of minimizing the extent of a cooling step between regeneration and reforming stages. Besides, due to the endothermic nature of the methane sorption enhanced reforming process at high temperatures, thermal energy must be provided to the SER process to achieve high CH 4 conversion and high carbon capture ratio. This can be made either in the form of high feed temperature or by utilizing the energy stored in the bed benefiting from the bed thermal capacity. • Dynamic heterogeneous model reveals the thermal behavior of the SER process. • Strategies to cover the energy demand for efficient H 2 production are assessed. • SER allows single step production of >95% purity hydrogen with >85% carbon capture rate. • Potential to avoid the cooling step between regeneration and reforming stages is demonstrated. [ABSTRACT FROM AUTHOR]

To alleviate the effect of solar radiation fluctuation on the solar volumetric reactor, phase change material (PCM) is applied to buffer the temperature vibration and improve the stability of thermochemical reactions. In this work, we analyzed the heat flow and distribution characteristics of the conventional double-walled volumetric reactor filled with PCMs (SVR1). We then proposed a novel solar volumetric reactor design (SVR2) to solve the problems of local high temperature, slow charging-discharging rate, and fluctuating methane conversion in various radiation conditions. The heat and mass transfer model coupled with thermochemical reaction kinetics was established to compare the performance of SVR1 and SVR2 under steady state, heat charging-discharging mode, and actual solar radiation fluctuation, respectively. The results show that compared to SVR1, the maximum temperature of SVR2 decreases by 106.3 K, and the minimum methane conversion rate increases from 77.4% to 93.6% under natural solar radiation fluctuation. [Display omitted] • A novel solar volumetric reactor filled with PCMs (SVR2) is proposed. • The location of the catalyst bed and the heat storage zone is rearranged. • The heat storage zone is composed of Na 2 CO 3 and SiC porous foam. • The radial temperature difference on the rear side of SVR2 is minimal. • The fluctuation of methane conversion rate in SVR2 decreases by 16.2%. [ABSTRACT FROM AUTHOR]

The highest‐temperature step in iodine–sulfur and hybrid–sulfur thermochemical cycles for hydrogen generation is the sulfuric acid decomposition reaction. To efficiently utilize solar energy directly to operate this step, the development of a catalytic solar receiver reactor is essential. A cavity‐type reactor coupled to a solar dish and a numerical analysis of the reactor predicting the reaction conversion as a function of the solar absorption coefficient is presented in this study. The catalytic receiver reactor consists of a double‐walled quartz cylindrical tube to form the cavity and a flat quartz plate window for entry of the concentrated solar radiation. Two catalysts, Fe1.8Cr0.2O3 and Fe2O3/SiO2, are tested in the solar catalytic receiver reactor and SO2 yields of ≈40% and 38% are observed, respectively. Numerical analysis of the reactor is performed and a reaction conversion–absorption coefficient correlation is established. For the catalytic packed bed assuming absorption coefficient of 0.65, a steady‐state temperature of 1212 K is achieved, accomplishing an approximate theoretical efficiency of ≈56%. The numerical analysis suggests that by utilizing a material of construction with high absorption coefficient, significantly enhanced sulfuric acid decomposition can be achieved by the cavity‐type solar receiver reactor. [ABSTRACT FROM AUTHOR]

Thermochemical heat storage is a key technology to solve the mismatch between supply and demand of renewable energy and realize long-term energy storage. This work is concerned about a shell-and-tube thermochemical energy storage reactor and its aim is to address a challenge associated the low reaction rate from the tube centre of the reactor due to low thermal conductivity of the storage material. We proposed the integration of porous copper thermal bridges into the reactor and examined the performance enhancement with a validated mathematical model. By optimizing the structural parameters (numbers, thickness, and porosity) of the thermal bridge, the discharging rate and water temperature of the reactor can be maximized while the fan's electricity consumption is reduced. The results show that, with the addition of the thermal bridges with optimal structural parameters, the total heat release and water peak temperature lift can be increased by 11.33% and 39.75%, respectively, with the peak outlet water temperature reaching 59.02 °C. Reducing air velocity from 0.428 m/s to 0.107 m/s, the fan's electricity consumption can be reduced by 85.07% and 91.72% in the charging and discharging processes, which can be reduced by another 62.34% and 16.55%, respectively, after adding the thermal bridge. • Porous thermal bridges integrated into a shell-and-tube thermochemical reactor (TCR). • Optimal numbers, thickness and porosity of thermal bridges were obtained. • Fan's electricity consumption (FEC) proposed as TCR performance evaluating indicator. • Improvement of TCR reaction rate and reduction of FEC achieved simultaneously. [ABSTRACT FROM AUTHOR]

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A novel graphite matrix was prepared by adding carbon black (CB) as a densification agent to traditional matrix A3-3 graphite preparation. The particle size of CB densifier we chose was approximately 50–150 nm, which was smaller than the pore diameter of densified matrix graphite (500-1000 nm). Five different mass fractions of CB were mixed and compared with as-received A3-3 by various characterization methods, which indicated that CB can effectively fill the pores of A3-3 and improve its anti-infiltration capability against molten salt (fluoride salt for molten salt reactor and heat storage salt). Meanwhile, considering the requirements for A3-3 graphite in scenarios of solid fuel molten salt reactor and thermal energy storage system, all the samples were compared as well before and after purification. The results showed that purification treatment resulted in slight increase of the pore size and open porosity of graphite and thus weakened its anti-infiltration capability against molten salt, but the thermal properties of graphite improved inversely. However, the addition of excessive CB could cause the significantly decline of thermal properties of A3-3. Comprehensively considering the anti-infiltration effect and requirements of thermal properties, adding 5 % CB was the most preferrable choice for the matrix graphite before and after purification. [Display omitted] [ABSTRACT FROM AUTHOR]

This work investigates the option of modifying the Advanced Test Reactor by replacing the current beryllium reflector with heavy water. Such a change may provide some potential benefits for not only increasing the thermal irradiation capabilities but also resolving other problems such as reflector integrity issues due to fast fluence damage, which is always a limiting factor in the lifetime of the current beryllium reflector. This paper presents the analysis and estimation of the ATR core physics parameters by replacing the current beryllium reflector with heavy water (D 2 O). The paper first describes the details of two selected conceptual designs, which are partially reflected with either beryllium or graphite, and how they are derived from the baseline beryllium reflector concept. Then, reactor physics performance parameters for the two new concepts are assessed by comparing with those of the baseline concept. The performance parameters considered in this paper include in-pile tube neutron and gamma fluxes and heating rates, maximum loop voiding reactivity, core power behavior with different power splits, predicted cycle length with a given fuel loading, and thermal hydraulic analysis with a higher lobe power split. It is important to note that this study focuses on the reactor physics aspects and does not delve into the engineering challenges associated with such a design modification. • Many of thermal test reactors, including ATR, are approaching their end of life. • Such test reactors suffer degradation of reflector materials due to the fast fluence. • However, the higher fluence is necessary to meet the high demands of experiments. • Alternative means of neutron reflectors other than Be reflector need to be examined. • Two types of D 2 O reflected core models and their characteristics are investigated. [ABSTRACT FROM AUTHOR]

• Machine-learning potential for the Zr-C-Ag ternary system was developed. • Ag diffusion in ZrC 0.94 and ZrC 0.97 was computed using molecular dynamics simulations. • Ag diffusion accelerates with higher temperature and increased C vacancy concentration. The ternary machine-learning interatomic potential for a Zr–C–Ag system was developed using first-principles calculations, moment tensor potential, and molecular dynamics simulations to calculate the diffusion coefficient of Ag in ZrC. The developed potential was utilized to investigate the vacancy formation energy, Ag substitutional energy, binding energy between Ag and vacancy, Ag interstitial energy, migration energy of Ag to an adjacent C vacancy in ZrC, and thermal expansion of ZrC. The results conformed to previously reported experimental and computational results, thereby validating the accuracy of the developed potential. The diffusion coefficients of Ag in ZrC 0.94 and ZrC 0.97 in the temperature range of 2800–3200 K were calculated using molecular dynamics simulations with the developed machine-learning interatomic potential. These calculation results can aid the safety analysis of radioactive 110mAg release in nuclear thermal propulsion reactors. [ABSTRACT FROM AUTHOR]

This paper assesses the time to radiation (radiotoxicity) and radiological (radiation risk) equivalence between natural uranium and radioactive waste of thermal and fast reactors at an increasing content of Np, Am, and Cm in radioactive waste. We calculate radiation risk by adapting models of the ICRP and other international organizations for the Russian Federation, taking into account background epidemiological indicators including cancer incidence, cancer mortality, and overall mortality. The radiation risk of internal exposure considers both the time after radionuclide intake and equivalent dose dynamics in human organs and tissues. To determine the time to radiological equivalence, we estimate the lifetime attributable risk of a single intake of natural uranium radionuclides and radioactive waste. An increase in the Np, Am, and Cm content of radioactive waste within 0.1–0.4% causes no effect on the radiological equivalence time, equal to ~100 years. However, a further increase from 0.5–0.8% prolongs the time to 300 years. A problem for optimizing the time to radiological equivalence is posed providing for waste storage costs and content of Np, Am, and Cm in long-lived radioactive waste. [ABSTRACT FROM AUTHOR]

• Optimizing the refueling time within the BN-800 reactor. • Proving a mathematical model of a system of three plugs with eccentricities. • Proving a mathematical model of large and medium plugs rotation in the BN-800. Sodium-cooled fast reactors (SFR) are included in the list of fourth-generation nuclear energy systems, the so-called generation IV (GEN-IV). It is the only technology of GEN-IV that possesses the significant practical experience of design, construction, and operation of high-power reactors. Due to the high temperature of the coolant at the BN-600 and BN-800 reactor core outlets, the steam generator produces steam with higher enthalpy, and this significantly increases the efficiency of cogeneration at SFR power plants in comparison with pressured water reactor (PWR) or boiling water reactor (BWR) units. The primary nuclear fuel effectiveness rises due to cogeneration with higher efficiency of a sodium-cooled fast reactor nuclear power plant (NPP) in comparison with thermal reactors. In addition, it is necessary to reduce the reactor refueling outages to improve the nuclear power plant utilization factor. It is possible to reduce the duration of the reactor refueling by the route optimization of the refueling machine movement. The prevailing in the world thermal neutron reactors with water cooling have a refueling machine that points the certain fuel assembly using two coordinates. The fast neutron reactors use sodium as a coolant; thus, there is a problem with its violent reaction with water and air oxygen. Therefore, it is necessary to exclude the contact of sodium and surrounding air during the refueling. To achieve this, the system of refueling machine pointing is used, consisting of two or three eccentrically located rotating plugs with hydraulic locks. The article presents the results of the creation of mathematical models of refueling machine movement and fuel assembly gripping. The time-optimal algorithms for the operation of refueling machines with three rotating plugs are proposed. The use of the new algorithm allows to reduce the time of movement of the grip of the refueling machine by 30–37%. [ABSTRACT FROM AUTHOR]