Search

As the fourth generation advanced reactor, the Brayton cycle system of small helium-xenon cooled reactor has the advantages of light weight, compact structure, simple system, fast start or stop, and is very suitable for the energy supply of remote areas and islands. Nuclear power plant is radioactive and highly hazardous after accidents, so it is very important to study its safety characteristics. In addition, helium-xenon cooled reactor is an advanced future reactor type, and its accident safety characteristics are not yet clear. Therefore, it is necessary to carry out the safety characteristics research of Brayton cycle system of small helium-xenon cooled reactor, especially under the condition of unprotected control. Firstly, based on Modelica language, through the modular dynamic modeling of key equipment, the accident safety characteristics analysis program of helium-xenon cooled reactor Brayton cycle system was developed. Secondly, the steady-state rated condition of the system was simulated, and the reliability of the accident safety characteristics analysis program of the system was preliminarily verified by comparing the error between the simulation value and the design value of the steady-state rated condition of the system, in which the maximum relative error is 2.31%. Finally, the transient conditions of various system accidents were simulated, and the dynamic response characteristics of transient conditions such as step introduction positive reactivity accident, step introduction negative reactivity accident, coolant incorrect charging accident and coolant incorrect discharging accident were analyzed. The results show that the simulation results of the system analysis program are reasonable. The reactor system has a certain self-stability and self-adjustment ability for step introduction positive reactivity accident and coolant incorrect charging accident under the condition of constant load and unprotected control. Under the conditions of step introduction positive reactivity accident and coolant incorrect charging accident, after the rotational speed increases by 21.6% and 12% respectively, it can be stabilized in another steady-state without protection and control. However, under the conditions of constant load and unprotected control, the reactor system can not be stabilized under another steady-state condition through self-regulation for the step introduction negative reactivity accident and the coolant incorrect discharge accident. Under the conditions of step introduction negative reactivity accident and coolant incorrect discharge accident, the corresponding rotational speed drop rate at 800 s is 85 rpm/s and 10 rpm/s respectively. It is necessary to control the rotational speed drop rate of the rotor through some protection and control measures to ensure the safety of reactor system. The relevant results provide a theoretical basis for the safety analysis of Brayton cycle system of helium-xenon cooled reactor.

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The highly loaded design method of helium compressors can effectively solve the difficulty in compressing helium in High Temperature Gas-cooled Reactors (HTGR). But it also causes obviously different attack angle characteristics of blade surface loads in a highly loaded helium compressor compared to air compressors. This difference inevitably affects separation characteristics and flow loss within the compressor. In the current study, the effects of highly loaded design methods and changes in attack angle on the separation characteristics of the compressor cascade are analyzed by applying a numerical simulation method first. Then, the influence of Mach number on the loss characteristics of the cascade for a highly loaded helium compressor is systematically analyzed. Finally, the effect of differences in the material properties of working fluid on the separation characteristics is discussed. The results indicate that the proportion of secondary flow loss to the total loss in highly loaded compressor cascades is 2.46 times larger than that in conventionally loaded ones. While the properties of working fluid have an effect on the performance of the compressor cascade, their effects on the weight factor of vortex loss are highly limited. [ABSTRACT FROM AUTHOR]

Hypersonic vehicles as next-generation aircraft have broad applications, but existing technologies of onboard power generation are hardly applicable due to the change of engines. In this research, a catalytic steam reforming enhanced closed-Brayton-cycle power generation system based on is developed. This system combines the closed Brayton cycle (CBC) and catalytic steam reformed fuel vapor turbine (CSRFVT) to supply electric power. The zero-dimensional models of CBC and the CSRFVT are established to evaluate system performance. Results indicate the products with a water content of 30% have the strongest working ability, which can reach 330 kJ/kg. Moreover, the thermal efficiency and electric power of the parallel arrangement are higher than that of the series arrangement. Besides, the lower pressure of water is beneficial to the electric power. However, the difference in electric power between various pressures is less than 1 kW. In addition, under the same heat absorption, the total electric power of the system based on fuel and water is higher, and the former's outlet temperature of cooling channels is lower. The maximum total electric power of the novel system is about 120 kW. This research provides an innovative technical solution for the power generation of hypersonic vehicles. • A novel power generation system based on hydrocarbon fuel and water is proposed. • A zero-dimensional model of the system performance is established. • The products with a water content of 30% have the strongest working ability. • The maximum total electric power of this system is 120 kW at Ma 6. Abstract. [ABSTRACT FROM AUTHOR]

The present research has analyzed the energy and exergy of a combined system of simultaneous power generation and cooling. To provide a comprehensive data sheet of this system, the system has been investigated in the temperature range of 300–800 °C, and 6 working fluids, including air, carbon dioxide, nitrogen, argon, xenon, and helium, have been investigated. The parameters affecting the performance of the system, namely the compressor inlet pressure, the compressor pressure ratio, and the intermediation pressure ratio were investigated. The power produced by the Brayton cycle at a pressure ratio of 5.2 is the highest due to the increase in compressor power consumption and turbine power generation. The results of the parametric study showed that the exergy efficiency of the system has the maximum value at the pressure ratio of 4.73. The results of the parametric study showed that increasing the pressure of the compressor does not have a significant effect on the electricity consumption and the temperature of the working fluid due to the constant pressure ratio. The input energy to the heat exchanger of the absorption chiller decreases with the increase in the Brayton cycle pressure ratio, and as a result, the cooling created by the chiller also decreases. In this method, three objective functions of exergy efficiency, energy efficiency, and total production power are considered as objective functions. The most optimal value of intermediation pressure ratio was obtained after the optimization process of 1.389. Also, the most optimal value of the pressure ratio of high-pressure and low-pressure turbines was reported as 2.563 and 1.845, respectively. [ABSTRACT FROM AUTHOR]

The growing demand for electricity in long-duration space missions has become a pressing concern. The space nuclear closed-Brayton-cycle (CBC) power generation system offers advantages in power output, operational lifespan, and range. However, a significant speed disparity exists between its compressor and alternator. To address this challenge, this paper proposes a double-rotor CBC configuration. A corresponding dynamic model that couples the nuclear reactor and radiator is formulated, and dynamic analysis is conducted to facilitate system control. The study delves into the dynamic start-up process of the double-rotor CBC system and examines how various component parameters impact its power generation performance. The findings indicate that through the introduction of suitable reactivity to regulate reactor power and the incorporation of a PID controller to manage flow distribution between two turbines, the system can achieve start-up within 5200 s. Moreover, the innovative double-rotor structure suggested in this paper enables the separation of compressor and alternator speeds. Consequently, the compressor and alternator can operate within their optimal speed ranges independently, which is a feature that holds potential benefits for the system's practical implementation. In addition, the steady-state operation of the system showcases the recuperator's heat transfer power at around 1127.60 kW, a parameter of significant importance. Following steady-state operation, the double-rotor CBC system demonstrated an electrical power output of 175.99 kW and a thermal efficiency of 32.38%. [ABSTRACT FROM AUTHOR]

Waste heat recovery is one of the main practices used to reduce the carbon footprint of the industrial sector regarding environmental concern. The supercritical carbon dioxide (s-CO2) cycle is one of the most attractive heat-to-power technologies; due to the abrupt variation in CO2 properties in the vicinity of its critical point, small compression work is required and finally a high cycle efficiency is achieved. In the literature, among the various proposed layouts, the recompression s-CO2 Brayton cycle is considered to be the most efficient one. The most critical component of such a cycle is definitely the main compressor, as the related usual design procedures have been developed in the past for ideal gas as a working fluid. This study presents a methodology for the preliminary design of a centrifugal compressor with a vaned diffuser, suitable for fulfilling the desired operating requirements of a particular supercritical CO2 recompression Brayton cycle. Furthermore, it demonstrates the numerical investigation of the three-dimensional (3D) flow phenomena occurring in it, focusing on the investigation of possible condensation. To this end, a one-dimensional flow model was developed to provide information regarding the geometry of the compressor and predict its prospective performance. Commercial computational fluid dynamics (CFD) software was then employed to examine the three-dimensional flow. The effect of accuracy in the evaluation of real gas properties approaching the critical point was examined, showing that a look-up table with more points around the critical point can reduce the numerical relative error by up to 0.3% for the value of specific heat capacity. In addition, the possibility of condensation occurrence was investigated at the impeller's inlet, where the flow is accelerated. The supersaturation pressure ratio was defined and implemented in order to identify regions where static pressure is lower than saturation pressure, possibly leading to local two-phase flow. [ABSTRACT FROM AUTHOR]

As a new type of large-scale energy storage system, pumped thermal electricity storage (PTES) requires frequent load variation to smooth out grid fluctuations. However, there is a lack of research on the variable load of PTES systems. Therefore, five variable load methods are innovatively proposed in this paper, and the dynamic characteristics of the closed Brayton cycle PTES system with liquid-phase storage are simulated for variable load, separately. The results show that: for the same total air discharge time, during charge process, the rotor speed fluctuation rates of the five modes are "air charge + low-pressure and high-pressure sequential air discharge (CLHS)" (+0.80%), "air charge + low-pressure air discharge (CL)" (+1.07%), "air charge + high-pressure air discharge (CH)" (+1.40%), "air charge + high-pressure and low-pressure sequential air discharge (CHLS)" (+1.51%), "air charge + high-pressure and low-pressure simultaneous air discharge (CHL)" (+2.51%), from small to large. During discharge process, the rotor speed fluctuation rates are "CL" (-3.31%), "CHLS" (-3.96%), "CLHS" (-4.39%), "CH" (-5.61%), "CHL" (-9.83%), from small to large. During both charge and discharge processes, the load regulation ranges are "CHL", "CLHS"/"CHLS", "CH", "CL", from large to small. It can be seen that the modes with smaller rotor speed fluctuation rates also have smaller load regulation ranges, while the modes with larger load regulation ranges have larger rotor speed fluctuation rates. Therefore, in operation, different variable load modes should be selected according to the actual needs of rotor stability and load regulation range. The results of this study can provide a reference for the actual operation of pumped thermal electricity storage system. [ABSTRACT FROM AUTHOR]

The optimization of the closed Brayton cycle results in the inlet condition of supercritical CO 2 (sCO 2) compressors being near the critical point. However, this proximity leads to decreased robustness and accuracy during numerical simulations. To enhance computational fluid dynamics (CFD) robustness and accuracy, a method utilizing Cubic B-spline smoothing is proposed to reconstruct thermodynamic properties using property look-up tables (LUTs). After revealing the characteristics and action mechanism of sCO 2 thermodynamic properties on the solver, effects of the method on solution robustness, accuracy, and the relationship with resolution are systematically investigated. The results demonstrate that this method effectively addresses the deficiencies arising from the inability of original LUTs to adapt to the high resolution and the presence of pseudo-convergence. The residuals achieve the convergence requirement in half the iteration steps compared to the original method, resulting in an over one-fold reduction in calculation time. The solution robustness is significantly enhanced by over tenfold, and the calculation accuracy is improved. This improvement increases the sensitivity of friction loss and secondary flow loss to drastic changes in thermodynamic properties. As a result, a highly robust and accurate performance prediction scheme for centrifugal compressor components is established. • Unveiling supercritical CO 2 characteristics and action mechanism on the solver. • Resolving poor solver robustness through thermodynamic property reconstruction. • Introducing a cost-effective and accurate robust compressor simulation method. • Addressing conflicts with high-resolution tables and pseudo convergence. [ABSTRACT FROM AUTHOR]

• Key dimension parameters of the PMG were obtained and the simulation model of PMG was established. • Comprehensive research on the electromagnetic field and loss calculation were performed. • The cooling paths of the PMG were designed and the resulting temperature profiles were calculated. • Different cooling schemes were compared and the appropriate cooling advice was proposed. The closed Brayton cycle (CBC) system is a prime energy conversion technology to convert heat from the reactor to electric power for space missions due to its light weight, compact and stable operation. The CBC system incorporates a permanent magnet generator (PMG) mounted on the CBC shaft with the turbine and compressor. To ensure safe operation of the CBC system, a small fraction of the working fluid is used to provide the required cooling. In this study, four different cooling schemes used in CBC system are concluded and the key dimensions of the PMG are obtained through mechanical design theory and electromagnetic theory. Comprehensive research on the electromagnetic field and loss calculation is then performed. Furthermore, the cooling paths of the PMG are designed and the resulting temperature profiles are calculated. Finally, different cooling schemes are compared and the appropriate cooling advice is proposed. [ABSTRACT FROM AUTHOR]

The growing demand for electricity in long-duration space missions has become a pressing concern. The space nuclear closed-Brayton-cycle (CBC) power generation system offers advantages in power output, operational lifespan, and range. However, a significant speed disparity exists between its compressor and alternator. To address this challenge, this paper proposes a double-rotor CBC configuration. A corresponding dynamic model that couples the nuclear reactor and radiator is formulated, and dynamic analysis is conducted to facilitate system control. The study delves into the dynamic start-up process of the double-rotor CBC system and examines how various component parameters impact its power generation performance. The findings indicate that through the introduction of suitable reactivity to regulate reactor power and the incorporation of a PID controller to manage flow distribution between two turbines, the system can achieve start-up within 5200 s. Moreover, the innovative double-rotor structure suggested in this paper enables the separation of compressor and alternator speeds. Consequently, the compressor and alternator can operate within their optimal speed ranges independently, which is a feature that holds potential benefits for the system’s practical implementation. In addition, the steady-state operation of the system showcases the recuperator’s heat transfer power at around 1127.60 kW, a parameter of significant importance. Following steady-state operation, the double-rotor CBC system demonstrated an electrical power output of 175.99 kW and a thermal efficiency of 32.38%.

Waste heat recovery is one of the main practices used to reduce the carbon footprint of the industrial sector regarding environmental concern. The supercritical carbon dioxide (s-CO2) cycle is one of the most attractive heat-to-power technologies; due to the abrupt variation in CO2 properties in the vicinity of its critical point, small compression work is required and finally a high cycle efficiency is achieved. In the literature, among the various proposed layouts, the recompression s-CO2 Brayton cycle is considered to be the most efficient one. The most critical component of such a cycle is definitely the main compressor, as the related usual design procedures have been developed in the past for ideal gas as a working fluid. This study presents a methodology for the preliminary design of a centrifugal compressor with a vaned diffuser, suitable for fulfilling the desired operating requirements of a particular supercritical CO2 recompression Brayton cycle. Furthermore, it demonstrates the numerical investigation of the three-dimensional (3D) flow phenomena occurring in it, focusing on the investigation of possible condensation. To this end, a one-dimensional flow model was developed to provide information regarding the geometry of the compressor and predict its prospective performance. Commercial computational fluid dynamics (CFD) software was then employed to examine the three-dimensional flow. The effect of accuracy in the evaluation of real gas properties approaching the critical point was examined, showing that a look-up table with more points around the critical point can reduce the numerical relative error by up to 0.3% for the value of specific heat capacity. In addition, the possibility of condensation occurrence was investigated at the impeller’s inlet, where the flow is accelerated. The supersaturation pressure ratio was defined and implemented in order to identify regions where static pressure is lower than saturation pressure, possibly leading to local two-phase flow.

Space nuclear reactor power (SNRP) using a gas-cooled reactor (GCR) and a closed Brayton cycle (CBC) is the ideal choice for future high-power space missions. To investigate the safety characteristics and develop the control strategies for gas-cooled SNRP, transient models for GCR, energy conversion unit, pipes, heat exchangers, pump and heat pipe radiator are established and a system analysis code is developed in this paper. Then, analyses of several operation conditions are performed using this code. In full-power steady-state operation, the core hot spot of 1293 K occurs near the upper part of the core. If 0.4 $ reactivity is introduced into the core, the maximum temperature that the fuel can reach is 2059 K, which is 914 K lower than the fuel melting point. The system finally has the ability to achieve a new steady-state with a higher reactor power. When the GCR is shut down in an emergency, the residual heat of the reactor can be removed through the conduction of the core and radiation heat transfer. The results indicate that the designed GCR is inherently safe owing to its negative reactivity feedback and passive decay heat removal. This paper may provide valuable references for safety design and analysis of the gas-cooled SNRP coupled with CBC. [ABSTRACT FROM AUTHOR]

Summary: This work analyzes the feasibility of integrating a modified commercial Capstone C30 microturbine unit into a non‐nuclear testbed developed for performance evaluation of microreactor design concepts. Testing will be conducted to provide detailed reactor core and heat removal section thermal hydraulic performance data for prototypical geometries and operating conditions and demonstrate integration with relevant power conversion units. The modified C30 power conversion unit (PCU) uses external electrical heating, rather than fossil fuel combustion, to provide a maximum power output of ~30 kWe in a closed Brayton cycle (CBC) loop using nitrogen as the working fluid. A 75 kWt electrically heated test article was evaluated as the heat source to provide a turbine inlet temperature of 600°C to the modified C30 PCU. The operation of a test article supplying a maximum thermal power of 250 kWt was also considered. The analyses performed here indicate that the CBC PCU will be capable of operating over a range of steady state and transient conditions to evaluate test article heat transfer performance in representative operational scenarios. Normal, off‐design operation and dynamic stability of the PCU are analyzed, and a proposed set of tests of the power control schemes and heat source‐PCU coupling are outlined. This study supports the timely development of microreactors intended for deployment by the end of this decade. [ABSTRACT FROM AUTHOR]

Summary: Space nuclear reactor power system (SNRPS), especially megawatt power level, is very attractive for the future civil and military space demands. The high‐temperature gas‐cooled reactor coupled with closed Brayton cycle (CBC) can achieve high‐power output for space applications. For the gas‐cooled SNRPS with CBC, dynamic models for all components, including reactor, turbine, compressor, alternator, ducting, pump, recuperator, gas cooler and heat pipe radiator, are developed in this article. Then, a transient system analysis code (SAC‐SPACE) is developed to perform the safety characteristics analysis of the SNRPS. In the full‐power steady‐state analysis, the maximum fuel temperature has a margin of 1323 K from the melting point. Moreover, the transient responses of the SNRPS under the mechanical failure of one Brayton loop (MFOBL1) and the reactivity insertion accident (RIA) are simulated and analyzed. During the MFOBL1, the maximum fuel temperature is 1275 K lower than the melting point, and finally, the reactor power stabilizes at 56.8% of the rated power. For the RIA, as long as the reactivity introduced into the core does not exceed 0.61 $, the SNRPS can reach a new steady‐state safely by itself without other protection strategies. It can be concluded that the SNRPS has good self‐stability due to the negative reactivity feedback of the reactor. This article may provide useful theoretical supports for the design and safety analysis of the gas‐cooled SNRPS with CBC. [ABSTRACT FROM AUTHOR]

The lithium-cooled reactor with Brayton conversion power system mainly consists of fast reactor, intermediate heat exchanger, closed Brayton cycle (CBC) loops filled with Helium–Xenon (He–Xe) binary gas mixtures and heat rejection loop which radiate residual heat through heat pipes to outer space. In this study, a dynamic model of 100-kWe lithium-cooled reactor with Brayton conversion power system was established based on RESYS code, which include reactor core thermal-hydraulic model, six-group neutron kinetics model and decay heat model, heat exchanger model, Closed Brayton cycle model including turbine, compressor and rotating shaft, heat pipe radiator model etc. The nominal steady-state simulation is carried out to verify the correctness and accuracy of individual component model the integrated system model. Four typical transient conditions including accidental reactivity insertion, loss of coolant flow of primary loop, partial and total external load loss and a step reduction in the mass flow rate of heat rejection loop are simulated to analysis the transient characteristics and prove the safety features for those simulated scenarios. The results are helpful for the design, evaluation and operation of space liquid-lithium-cooled reactor power system with He–Xe closed Brayton cycle. [ABSTRACT FROM AUTHOR]

The compressor of closed Brayton cycle (CBC) plant operating with working fluid other than air is a vital element of the energy conversion unit. However, due to insufficient understanding of the influence of the physical properties of working fluids on the performance of the compressor, the actual working conditions and design conditions of the compressor's performance deviate greatly. In this paper, the objective is to analyze the influence mechanism of the physical properties on the performance of the cascade of compressor (static pressure ratio and total pressure loss coefficient). Therefore, the impact of a specific heat ratio on the performance of the compressor cascade is studied utilizing carbon dioxide (γ = 1.29), air and carbon monoxide (γ = 1.4), argon and helium (γ = 1.667). Moreover, the relationships of static pressure ratio and total pressure loss coefficient with physical properties of the working fluids are analyzed in the compressor cascade. It is established that a higher specific heat ratio fluid gives a higher coefficient of total pressure loss and static pressure ratio in contrast to smaller specific heat ratio at matching inlet Reynolds number and Mach number. [ABSTRACT FROM AUTHOR]

Thermodynamic cycles are currently the most wanted means of converting nuclear power into available work due to the higher conversion efficiencies provided. Rankine cycles have been greatly applied for terrestrial reactors and nuclear submarines, while a lot of space projects have been using Brayton cycles for power conversion mainly due to mitigation in power-to-radiator area ratio. Regenerative Brayton cycles can present a considerable power conversion efficiency improvement when compared to the regular ones because of a reduction on the power demand from the hot heat exchanger of a cycle to achieve the same net output power. In this work, a cross-flow heat exchanger with He-Xe (40 g/mol) working fluid and Inconel 617 structural material used as the recuperator for the closed Brayton cycle of a nuclear reactor applicable for space systems is assessed in terms of heat transfer performance. The recuperator tubes are arranged in a staggered distribution around the exchanger axis. The matrix of tubes has a fixed count of 4 rows along the exchanger axis, while the number of tubes around the axis is variable, where the samples of 5, 7, 9, 12 and 16 are tested. The characteristic curves of heat transfer rate, effectiveness, convection coefficient and Colburn factor are built for each of the studied geometries in function of the Reynolds number. The obtained values for each of these parameters range between 1892.49 and 8493.21W (heat transfer rate), 0.165 and 0.325 (effectiveness), 60.3822 and 176.9682 W/m2K (cold side convection coefficient), 30.3276 and 104.3263 W/m2K (hot side convection coefficient), 0.0071 and 0.0109 (cold side Colburn factor), 0.0523 and 0.1370 (hot side Colburn factor).

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• A one-dimensional model is developed for the reactor to search the minimum mass according to the thermal–hydraulic limitations. • A He-Xe gas-cooled reactor coupled with a Closed Brayton cycle is optimized in terms of system mass and thermal efficiency. • Masses of the reactor core and coolers dominate the total mass in most cases. • Increasing the recuperator effectiveness from 90% is required for thermal efficiencies above 40%, but its mass can surpass that of other components. Nuclear microreactors represent an option for distributed power generation, which can be deployed in military installations, remote off-grid villages, and locations recovering from natural disasters. Small system mass is necessary to achieve their mobility. In this study, a He-Xe gas-cooled reactor coupled with a Closed Brayton cycle (CBC) is optimized in terms of system mass and thermal efficiency. A single-channel model is developed for the reactor to predict the minimum mass according to the thermal–hydraulic limitations. Masses of the heat exchanger and turbo-machines are calculated based on empirical curves. The simple regenerative and intercooling cycles are considered. A parametric study is conducted to investigate the influence of key parameters on system mass and to explore the tradeoffs between different components that satisfy the power requirements of 8 MWe. Furthermore, the Non-dominated Sorting Genetic Algorithm (NSGA-II) is used to optimize the system mass and thermal efficiency. Optimal values of critical parameters on the Pareto Frontier are presented and discussed. Results show that the masses of the reactor core and coolers dominate the total mass in most cases, and increasing the height of the reactor core can help reduce the system mass by allowing a smaller core radius. The Pareto Frontier shows that at thermal efficiencies around 40% or below, the system mass is depressed by using large CPR, molecular weight of the mixture, height of the reactor core, and small recuperator effectiveness. Increasing the recuperator's effectiveness from about 90% is required for higher thermal efficiency design, but its mass increases dramatically and can surpass the mass share of other components. The current analysis can provide a guide for detailed system and component design. [ABSTRACT FROM AUTHOR]

• The application background of helium compressor is introduced. • The theoretical research of helium compressor is reviewed. • The challenges and potential breakthroughs were highlighted. The power conversion unit of a high-temperature gas-cooled reactor (HTGR) could be a closed Brayton cycle power plant with helium as the working fluid. The helium compressor is the main component of such a power conversion unit, and its performance has significant effects on the power output and cycle efficiency. However, helium is difficult to compress owing to its thermo-physical properties, making the helium compressor design challenging. This paper provides a review of the studies and applications of helium compressors. The background of the helium compressor is introduced, the theoretical studies on helium compressors are reviewed and the development of the helium compressor is discussed. Based on the review, the helium compressor future challenges and potential breakthroughs in different aspects are highlighted. The results show that helium compressor development requires a special design technique which takes the thermo-physical properties of helium into consideration and advanced technologies suitable for helium compressor should focus on development. [ABSTRACT FROM AUTHOR]

Highlights • Three independent variables are derived from the model of space Brayton cycle. • Three control methods are envisaged: inventory, rotating speed, and bleed controls. • Performance of off-design conditions and load rejection accident are investigated. Abstract The closed Brayton cycle system is a potential choice for the power conversion system for future space nuclear reactors owing to its high energy-conversion efficiency and compact configuration, especially with regard to high power demand. The load change requires a rapid and safe adjustment of the power generation unit. Thus, the off-design features are key for understanding and designing the control schemes of the space nuclear Brayton cycle. In this study, a cycle's model is established and three independent variables are derived from the model with constraints. The corresponding control methods in theory are envisaged based on the model: inventory control, bleed control, and rotating speed control. The control mechanism and system performance under off-design conditions with these three methods are investigated, and it is observed that inventory control can maintain high efficiency when the electric load changes in a large scope. Bleed control can adjust output power in a relatively narrow range but can be used to prevent the over-speed of a turbomachine in case of a load rejection accident. The reduction in the rotating speed can decrease the output power to match the change in electric load quickly. It is an effective and important control method for the space Brayton cycle system. The results are helpful for the design and operation of space Brayton cycle system. [ABSTRACT FROM AUTHOR]

Highlights • The experimental tests on performance of helium compressors were implemented. • The applicability of the design methods of the helium compressors was verified. • The complete performance of the full-scale helium compressor was obtained. Abstract In the six candidate types of the fourth-generation nuclear power system, the Helium Gas Turbine System (HGTS) will be the ideal power conversion system for both the Modular High Temperature Gas-cooled Reactor (Modular HTGR) and the Gas-cooled Fast Reactor. The main advantages of HGTS are the compact and simple configuration and the high power-generation efficiency by taking advantage of high temperature heat source. At present, one of the main research contents of HGTS in China is helium compressors in HTR-10GT project. Previous researches showed that the aerodynamic performance of the helium compressors was one of the key factors of the efficiency of HGTS and had direct influences on the efficiency of the system. With different working fluids, features of helium compressors are different from conventional compressors. There were very limited experimental and theoretical studies in the research field of helium compressors. In this paper, a performance test system for the full-stage and full-scale helium compressors was employed to test and investigate the performance of the helium compressors of HTR-10GT, including pressure ratio, efficiency and surge and block boundaries. The performance of the high-pressure compressor (HPC) was measured at rated conditions and at different rotating speeds and different inventory levels. The results showed that the pressure ratio of the HPC satisfied the requirements of the HGTS, and the efficiency of the HPC was below expectation. The experimental study represented the applicability of the helium compressor design methods and provided the key aerodynamic performance data for future studies, such as off-design conditions, studies on compressor design methods and further improvement on the performance of the helium compressors. [ABSTRACT FROM AUTHOR]

Abstract Helium Gas Turbine System (HGTS) has compact and simple configuration, and can make full use of high temperature heat source to achieve high power generation efficiency. It will be the desirable power conversion system for the Modular High Temperature Gas-cooled Reactor (Modular HTGR) in the future. But there are some technical challenges to be solved for HGTS, including helium compressor and active magnetic bearings, etc. Helium compressor is key component for HGTS. Its aerodynamic performance had direct influences on the efficiency of the HGTS. Its features are different from those of conventional air compressors or gas turbines due to the different working fluids. The experimental and theoretical studies on helium compressors were very limited. In this paper, a performance test system for HTR-10GT project was established for the full-stage and full-scale helium compressors. Performance of low-pressure compressor (LPC) of HTR-10GT was tested and investigated on this test system. The pressure ratio and efficiency of the LPC were obtained at rated conditions and at different rotating speed, different inventory level. Surge and block boundaries of LPC were also explored. The results showed that the performance of LPC satisfied the design requirements. And the experimental study in the paper verified the validity and effectiveness of the design methods of the helium compressors at the LPC conditions, and provided the key aerodynamic performance data for further studies, such as off-design conditions, inventory control and load rejection control. Highlights • The experimental tests on performance of helium compressor were implemented. • The validity of the design methods of the helium compressor was verified. • The complete performance of the helium compressor was obtained. [ABSTRACT FROM AUTHOR]

The compressor of closed Brayton cycle (CBC) plant operating with working fluid other than air is a vital element of the energy conversion unit. However, due to insufficient understanding of the influence of the physical properties of working fluids on the performance of the compressor, the actual working conditions and design conditions of the compressor’s performance deviate greatly. In this paper, the objective is to analyze the influence mechanism of the physical properties on the performance of the cascade of compressor (static pressure ratio and total pressure loss coefficient). Therefore, the impact of a specific heat ratio on the performance of the compressor cascade is studied utilizing carbon dioxide (γ = 1.29), air and carbon monoxide (γ = 1.4), argon and helium (γ = 1.667). Moreover, the relationships of static pressure ratio and total pressure loss coefficient with physical properties of the working fluids are analyzed in the compressor cascade. It is established that a higher specific heat ratio fluid gives a higher coefficient of total pressure loss and static pressure ratio in contrast to smaller specific heat ratio at matching inlet Reynolds number and Mach number.

According to versatile and long-lasting requirements of deep space missions, space nuclear reactor (SNR) power system is becoming a more suitable choice compared to traditional solar and chemical power systems in large-scale and long-life applications. From NASA’s previous research, the gas-cooled reactor along with closed Brayton cycle (CBC) could achieve optimized weight-power ratio and be more applicable for large power system (100 kWe or MWe level). In this paper, a concept of integrated gas-cooled space nuclear reactor named IGCR-200 is introduced, which is designed based on the TRISO particle fuel and could achieve 200 kWe output combined with highly efficient He/Xe CBC generator. The design requirements include an operation lifetime of at least 10 years in full power mode, maximum fuel temperature < 1600K, negative temperature reactivity feedback, passive decay heat removal, redundancy in reactor control, and sub-criticality during water flooding accidents. It has an outer diameter of 70.0 cm, a height of 66.0 cm (reactor part), a total mass around 1000 kg, total Uranium inventory of 226.8 kg (235U enrichment as 93%), and 1 MW thermal power output. The reactor physics, thermal hydraulics and other required analysis are taken out to show the feasibility and performances of the design.

Rapid development of the aviation industry has brought great convenience to people's travel and goods transportation. The inevitable issues are high level of energy consumption and the huge environment pollution by kerosene combustion. On the other hand, there is a greater requirement for the electricity capacity as well as the power ratings of aircraft generators to meet the continuous intensification of the electrification degree in modern aircraft. The question that is tried to identify in this paper is: can the waste heat in the aircraft be collected to generate power for meeting the electricity demand? In this paper, an electricity supply system driven by the heat collected from the commercial aeroengine wall is first proposed. It is an integrated system by coupling the topping gas turbine with bottomed closed Brayton cycle via the liquid sodium. A comprehensive mathematical model is developed for the system in the aspects of thermodynamics and economics. The analysis results demonstrate that the proposed system is capable of satisfying the megawatt-scale power requirements of commercial aeroengine. The fluid He–Xe (40 g/mol) is a better choice to cycle the given power system than He and air considering its larger net power output, lower compression ratio and smaller component size. The system with He–Xe can supply 1299 kW electricity power when the compression ratio is just about 7.1. In that case, the oil cost savings is about 3.66 percentages lower than that of the original oil consumption. • Novel electricity system is given by using waste heat of commercial aeroengine. • Effects of different working fluids and operation parameters are examined. • He–Xe (40 g/mol) is recommended as the system working fluid than air and He. • The compression ratio is suggested at 7.1with an operation pressure of 3.55 MPa. • Oil cost savings is about 3.66% lower than that of original oil consumption. [ABSTRACT FROM AUTHOR]

Heat pipe cooled reactors with closed Brayton cycle (CBC) have the potential of achieving both high efficiency and high safety. However, the coupled characteristics and performance of CBC coupled with heat pipe reactors have not been well studied. Few works consider both the neutron dynamics in heat pipe cooled reactors and the dynamic heat and mass transfer in CBC. In this paper, a novel nuclear power system configuration, heat pipe cooled reactor with CBC, is proposed and comprehensively analyzed. A dynamic model is built based on the modular modeling idea, and verified using a Brayton cycle test bench. The proposed system has load following capability within certain motor speed, and its maximum thermal-electric energy conversion efficiency exceeds 20%. The dynamic charge amount control strategy is further proposed to improve efficiency. The maximum efficiency improvement is about 5% at 2kWe. The self-power-regulation and inherent passive safety of the reactor are verified through dynamic simulation. The power and temperature overshoots of the dynamic responses are selected as quantitative indicators of system dynamic performance. MAPs of the temperature and power overshoots for unit changes in output power are obtained, and can be used to evaluate the system safety during dynamic operations. • Coupled dynamic model of heat pipe cooled reactor and closed Brayton cycle. • Considering both the neutron dynamics and dynamic heat and mass transfer. • Dynamic charge amount control strategy for higher energy conversion efficiency. • MAPs for evaluating the efficiency and safety of the system. [ABSTRACT FROM AUTHOR]

To exploit the advantages of Fluoride-Salt-cooled high-Temperature Advanced Reactors (FuSTAR) such as high temperature, inherent safety, compact structure, and modularization, an energy conversion system based on a closed Brayton cycle was adopted, and the superstructure design was optimized to attain the best parameters and configuration. To enhance the convergence rate of a single computation, the simultaneous equation method was employed, while the particle swarm method was utilized to prevent local optimality. Irreversible analysis and sensitivity analysis were performed to evaluate the system's performance. The findings demonstrate that thermal efficiency can be significantly enhanced by incorporating reheating into the system. Furthermore, for air and Ar, the recompression intercooling configuration proved effective in reducing the heat transfer temperature difference and enhancing thermal efficiency. For CO2 and Xe, the incorporation of reheating, recompression, and intercooling significantly improved thermal efficiencies beyond 53%, indicating their immense potential for further development. Introducing reheating into the Xe cycle led to a substantial increase in both thermal efficiency and the area of the temperature-entropy graph. The irreversible analysis revealed that for CO2 and SF6, the predominant loss occurred in the cooler and recuperator. In contrast, for the Xe cycle, all kinds of irreversible losses were evenly distributed across each device. Sensitivity analysis indicated that the thermal efficiency of near-critical fluids was more sensitive to the lowest pressure than that of far-critical fluids. Both the near-critical split ratio and the far-critical minimum pressure had a significant impact on the mass flow rate. The design results of this method can guide the selection of the optimal power cycle system configuration for FuSTAR. [ABSTRACT FROM AUTHOR]

The long lunar night, which cannot be powered by solar energy, brings a huge challenge to the lunar base energy system. Closed Brayton cycle (CBC) system is considered as an effective solution, but cannot be driven by low temperature heat sources. Organic Rankine cycle (ORC) system is used to couple into the CBC system to recover waste heat and produce more electricity. In this paper, a mathematical model of CBC-ORC system driven by collector or heat storage unit is developed, the variation of thermal efficiency, exergy destruction, and Brayton-Rankine rotating unit (BRRU) mass is evaluated during the whole lunar day. Results are as follows: when the helium mole fraction is 0.9, CBC stops on the day of 7.7 at night, which is earlier than the stop time for other helium mole fractions. The maximum power generation can reach 169.21 kW. Thermal and exergy efficiency can reach 34.49% and 31%, respectively. After three-objective optimization, the results of thermal efficiency (30.07%), exergy destruction (169.62 kW) are similar to the basic working condition, and the BRRU mass (720.3 kg) can be extremely reduced by 78.76% compared to the basic working condition, which is essential to the practical applications. • Energy system model is established by combining lunar environmental parameters. • Adjusting CBC maximum operating pressure can reduce BRRU mass by up to 11.47%. • Helium mole fraction significantly alters the stop time of CBC at the lunar night. • Increasing the condensing temperature can reduce the system mass by 22.51%. • CBC maximum operating pressure is meaningful for adjusting the distribution of exergy. [ABSTRACT FROM AUTHOR]

Introduction- Actually in Colombia, there is great interest in the application of renewable energy and the diversification of the energy matrix. Therefore, in this work, are presented the results of the simulation of a hybrid solar thermal plant of closed Brayton cycle in Colombia, that receives heat from a concentration system of central tower and heliostats. The solar resource is estimated by a time model validated initially, additionally with a combustion chamber that uses natural gas as fuel, which guarantees the stability of the heat supplied to the plant. The location of the plant is selected based on the global and diffuse average monthly radiation per day, and additionally, a simulation of the main operating parameters is carried out, optimizing the power and overall performance as a function of the pressure ratio. Finally, an exergy analysis of the plant is developed, especially of the components affected by the variation of the radiation during the day. Objective- Evaluate a thermal solar plant of closed Brayton cycle concentration, through an energetic and exegetical analysis under the environmental conditions of Colombia. Methodology- Integrate a model of solar resource, an energetic model and an exergy model applied to the environmental conditions of Colombia in model language in a Dymola compiler. Results- The evolution of the main operating parameters of the plant throughout the day, the variation of the performance and the power depending on the pressure ratio are presented and analyzed. Conclusions- It is technically feasible the operation of a solar thermal plant of concentration of Brayton cycle in some places of Colombia, given the available solar resource and the fuel saving that it generates despite the detriment of the energetic and exegetical performance. [ABSTRACT FROM AUTHOR]

With gradual increase in reactor outlet temperature, the efficient power conversion technology has become one of developing trends of (very) high temperature gas-cooled reactors (HTGRs). In this paper, different cycle power generation schemes for HTGRs were systematically studied. Physical and mathematical models were established for these three cycle schemes: closed Brayton cycle, simple combined cycle, and reheated combined cycle. The effects and mechanism of key parameters such as reactor core outlet temperature, reactor core inlet temperature and compression ratio on the features of these cycles were analyzed. Then, optimization results were given with engineering restrictive conditions, including pinch point temperature differences. Results revealed that within the temperature range of HTGRs (700–900 °C), the reheated combined cycle had the highest efficiency, while the simple combined cycle had the lowest efficiency (900 °C). The efficiencies of the closed Brayton cycle, simple combined cycle and reheated combined cycle are 49.5%, 46.6% and 50.1%, respectively. These results provide insights on the different schemes of these cycles, and reveal the effects of key parameters on performance of these cycles. It could be helpful to understand and develop a combined cycle coupled with a high temperature reactor in the future. [ABSTRACT FROM AUTHOR]

Sodium-cooled fast reactor (SFR) is considered the most promising of the Generation IV reactors for their near-term demonstration of power generation. Small modular SFRs (SM-SFRs) have less investment risk, can be deployed more quickly, are easier to operate and are more flexible in comparison to large nuclear reactor. Currently, SFRs use the proven Rankine steam cycle as the power conversion system. However, a key challenge is to prevent dangerous sodium-water reaction that could happen in SFR coupled to steam cycle. Nitrogen gas is inert and does not react with sodium. Hence, intercooled closed Brayton cycle (CBC) using nitrogen as working fluid and with a single shaft configuration has been one common power conversion system option for possible near-term demonstration of SFR. In this work, a new two shaft nitrogen CBC with parallel turbines was proposed to further simplify the design of the turbomachinery and reduce turbomachinery size without compromising the cycle efficiency. Furthermore, thermodynamic performance analysis and preliminary design of components were carried out in comparison with a reference single shaft nitrogen cycle. Mathematical models in Matlab were developed for steady state thermodynamic analysis of the cycles and for preliminary design of the heat exchangers, turbines and compressors. Studies were performed to investigate the impact of the recuperator minimum terminal temperature difference (TTD) on the overall cycle efficiency and recuperator size. The effect of turbomachinery efficiencies on the overall cycle efficiency was examined. The results showed that the cycle efficiency of the proposed configuration was comparable to the 39.44% efficiency of the reference cycle. In addition, the study indicated that the new configuration has the potential to simplify the design of turbomachinery, reduce the size of turbomachinery and provide opportunity for improving the efficiency of the turbomachinery. The findings so far revealed that the proposed two-shaft CBC with nitrogen as working fluid could be a promising power conversion system for SM-SFRs near-term demonstration. [ABSTRACT FROM AUTHOR]

An irreversible regenerative closed Brayton cycle has been optimized using a thermoeconomic objective criterion which is defined as the ratio of net power output to the total cost rate. The total cost rate includes fuel, investment, environmental and operation & maintenance cost rates. In the considered model pressure drops, heat leakages, irreversibilities due to finite-rate heat transfer and internal dissipations have been included. The effects of design parameters, such as isentropic temperature ratio of compressor and turbine, regenerator effectiveness, pressure loss parameter of the cycle, on the general and optimal thermoeconomic performances have been investigated in detail. The results of the study will be helpful for the performance analysis and optimization of practical Brayton heat engine systems. [ABSTRACT FROM AUTHOR]

This article proposes a novel power plant comprising a closed Brayton cycle (CBC) and a Rankine cycle (RC) coupled in series with respect to the flue gases instead of a conventional combined cycle, where the cold energy of the LNG is used to cool the CBC compressor suction. The research study focuses on finding working fluids best suited to the proposed CBC-RC plant and on achieving high efficiency. The proposed working fluids that fulfil the requirements for the CBC are He, N2 and for the RC are CO2, ammonia, ethanol or water. An analysis of the power plant using different working fluids is carried out and it is ascertained that the best efficiency conditions for the CBC are achieved with He and CO2 for the RC. As a result, a thermal efficiency of 67?60%, an overall efficiency of 55?13% and a specific power of 2?465 MW/(kg s-1 LNG) is achieved. [ABSTRACT FROM AUTHOR]

Abstract: One promising avenue for the development of next generation CST (Concentrating Solar Thermal) technology focuses on the use of a direct-heated sCO2 (supercritical-CO2) CBC (closed Brayton cycle) as the generator power cycle. Initial investigations into such a CST plant, while promising, have found its power output and efficiency to be sensitive to fluctuations in solar heat input and ambient temperature over a day and between seasons. Given the difficulty in developing complete models across all operating conditions due to non-linearities in CO2 properties, an extremum-seeking controller is proposed to maximise the power output of the CBC as the solar heat input and cooling-air temperatures change. This controller achieves this effect by manipulating the CO2 mass inventory in the CBC. Slack variables are introduced into the extremum-seeking control performance metric to impose constraints on turbine inlet temperature and pressure to protect the CBC from damage. The performance of the proposed scheme is tested through simulations on representative summer and winter days. Simulations indicate that the performance of the CBC under ESC (extremum-seeking control) based inventory-control compares favourably to operation with a fixed-CO2 inventory in both summer and winter and does not require retuning between seasons. [Copyright &y& Elsevier]

In this study, an elastohydrodynamic model was created for predicting the pressure field in a compliant thrust bearing assembly lubricated by high pressure CO2. This application is of significance due to ongoing research into the closed-cycle supercritical CO2 turbine as a high-efficiency alternative to steam turbines. Hardware development for this concept has been led by Sandia National Laboratories, where turbomachinery running on gas foil thrust and journal bearings is being tested. The model accounts for the fluid velocity field, hydrodynamic pressure, and frictional losses within the lubrication layer by evaluating the turbulent Reynolds equation coupled with an equation for structural deformation in the bearings, and the fluid properties database RefProp v9.0. The results of numerical simulations have been compared with empirical correlations, with reasonable agreement attained. Of particular interest is the contrast drawn between the performance of high pressure CO2 as a lubricant, and ambient pressure air. Parametric studies covering a range of fluid conditions, operating speeds, and thrust loads were carried out to illustrate the value of this model as a tool for improved understanding and further development of this nascent technology. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the relative hot-to-cold side volume-ratios on dynamic characteristics of a CBC (closed Brayton cycle) with sCO2 (supercritical carbon-dioxide) as the working-fluid is investigated in this study. The analysis of the CBC is conducted in the context of power generation in a direct-heated (no thermal-oil loop) and dry-cooled parabolic-trough solar thermal power plant, using a control-oriented model of the CBC. Dynamic performance of the sCO2 CBC with different relative volume-ratios between the hot and cold sides of the sCO2 CBC is compared using simulations for conditions on a representative summer day. The CBC hot-to-cold side volume-ratio influences CO2 mass movement and hence power output. Increasing the hot-to-cold side volume-ratio in the CBC results in a slower, more gradual dynamic response when there are fluctuations in solar heat input and ambient air temperatures. The dynamic response characteristics of a CBC with a hot-to-cold side volume-ratio less than one are shown to differ significantly from a CBC with a volume-ratio greater than or equal to one. [Copyright &y& Elsevier]

Abstract: The dynamics of a direct-heated closed Brayton power conversion system (PCS) with supercritical carbon-dioxide as the working-fluid (sCO2 PCS) is investigated in this study. Simulations of the dynamic response of the sCO2 PCS to changes in ambient air temperatures and solar energy input from parabolic trough collectors on representative days for summer and winter are presented. A control-oriented model describing sCO2 PCS dynamic behaviour has been constructed using mathematical models of heat-exchangers and turbomachinery. Changes in solar heat input causes movement of carbon-dioxide (CO2) mass between the hot and cold-sides of the PCS. Movement of mass results in variations in CO2 mass-flow rate, pressures, temperatures, and net-power output. The sCO2 PCS maintains a relatively stable net-power output when operating under conditions representative of an average day in summer with capped heat input. Turbine inlet temperatures rise well above nominal values due to reductions in CO2 mass-flow rates. A significant power output penalty is incurred on a winter day due to conditions at the compressor inlet becoming subcritical. The simulations highlight the potential for utilising CO2 charge manipulation for sCO2 PCS mass-flow rate control in summer, and the need for control of compressor inlet conditions in winter, for sustained fully supercritical operation of the PCS within allowable limits. [Copyright &y& Elsevier]