Reactor Outlet Temperature Research Articles

Performance analysis of the temperature-upgraded flash-driven low-temperature advanced natural circulation heating reactor system

To address the current deficiencies in outlet temperature and thermal power of low-temperature heating reactors while ensuring safety and economic viability, this study introduces the Temperature-Upgraded Flash-driven Low-temperature Advanced Natural Circulation Heating Reactor (TU-FLANC). The FLANC system innovatively utilizes the flashing phenomenon of the coolant in the rising channel to significantly increase the coolant circulation flow rate and thus enhance thermal power at atmospheric pressure. The TU system employs an Absorption Heat Pump (AHP) to upgrade the temperature of the reactor’s output heat. The two systems are interconnected via a Coupled System Heat Exchanger (CSHEX), achieving an upgrade in reactor thermal power and outlet temperature at atmospheric pressure. To evaluate the performance of the TU-FLANC system, a mathematical model of the system was established, and a computational program was developed. The impact of key parameters such as evaporator temperature, condenser temperature, and solution concentration on system performance was analyzed. The results indicate that the evaporator temperature and solution concentration have the most significant impact on the system’s coefficient of performance (COP) and the coefficient of performance considering pump work (COPW). Through Differential Evolution (DE) algorithm optimization, the optimal solution concentration combinations were determined to maximize COP and COPW under different temperature upgrade demands. For a temperature upgrade demand of 50 °C, the optimal solution concentration combinations are 40.02 % and 57.48 %, with corresponding COP and COPW values of 0.5282 and 0.4886, respectively. The research findings highlight the significant innovative potential of the TU-FLANC system in enhancing heat power and outlet temperature.

Reinforcement Learning-Based Control Sequence Optimization for Advanced Reactors

The last decade has seen the development and application of data-driven methods taking off in nuclear engineering research, aiming to improve the safety and reliability of nuclear power. This work focuses on developing a reinforcement learning-based control sequence optimization framework for advanced nuclear systems, which not only aims to enhance flexible operations, promoting the economics of advanced nuclear technology, but also prioritizing safety during normal operation. At its core, the framework allows the sequence of operational actions to be learned and optimized by an agent to facilitate smooth transitions between the modes of operations (i.e., load-following), while ensuring that all safety significant system parameters remain within their respective limits. To generate dynamic system responses, facilitate control strategy development, and demonstrate the effectiveness of the framework, a simulation environment of a pebble-bed high-temperature gas-cooled reactor was utilized. The soft actor-critic algorithm was adopted to train a reinforcement learning agent, which can generate control sequences to maneuver plant power output in the range between 100% and 50% of the nameplate power through sufficient training. It was shown in the performance validation that the agent successfully generated control actions that maintained electrical output within a tight tolerance of 0.5% from the demand while satisfying all safety constraints. During the mode transition, the agent can maintain the reactor outlet temperature within ±1.5 °C and steam pressure within 0.1 MPa of their setpoints, respectively, by dynamically adjusting control rod positions, control valve openings, and pump speeds. The results demonstrate the effectiveness of the optimization framework and the feasibility of reinforcement learning in designing control strategies for advanced reactor systems.

The investigation of thermo-economic performance for dry-cooled closed Brayton cycle coupled to nuclear microreactors using different coolants

Dry-cooled closed Brayton cycle (CBC) coupled to gas-cooled nuclear microreactors offers a compact structure and can be deployed in water-deficient areas. The gas-cooled reactor utilizes coolants including supercritical carbon dioxide (S–CO2), helium, and He–Xe mixture. The choice of working fluids for CBC strongly affects its size and performance, where smaller plant sizes, higher thermal efficiency, and lower investments are preferred. This study investigates the thermo-economic performances of dry-cooled CBC coupled to nuclear microreactors using different coolants. A design method for dry-cooled CBC is developed based on the integration of thermodynamic modeling and component preliminary design. Baseline designs are first established, followed by an analysis of the effects of key design parameters. Furthermore, a multi-object optimization is conducted to compare the Pareto frontiers of CBC using different working fluids. The results demonstrate that the helium simple cycle exhibits superior efficiency and precooler size due to its higher reactor outlet temperature, though with a larger capital cost. The Pareto frontier of the He–Xe cycle is worse than that of the helium cycle. The S–CO2 recompression cycle has a comparable efficiency with a smaller capital cost at mediate reactor outlet temperatures but suffers from large precooler sizes. The findings revealed that the S–CO2 recompression cycle is a more promising choice if the reactor outlet temperature can be further elevated.

Characteristic analysis of natural circulation residual heat removal in small reactor

In order to study the characteristics of small helium-xenon cooled nuclear reactor that only relies on natural circulation to remove residual heat after shutdown, this paper carries out geometric and physical modeling of helium-xenon cooled nuclear reactor, and uses CFD to simulate the process of natural circulation residual heat removal. Variation laws of the hot spot temperature on the surface of fuel cladding and the mass flow of helium-xenon mixed gas under different working conditions are calculated, and the transient characteristics of temperature, flow and other related parameters in the system loop are analyzed. The calculation results show that during the natural circulation residual heat removal process, the overall change trend of the hot spot temperature on the surface of the fuel cladding, the average temperature of the primary coolant and reactor outlet temperature first rises to the highest value and then decreases, and the mass flow of helium-xenon mixed gas shows an exponential decay trend; Increasing the initial mass flow of helium-xenon mixed gas and reducing the residual heat of the reactor core can reduce the maximum hot spot temperature on the surface of the fuel cladding. The relevant research results provide a useful reference for the optimal design of natural circulation residual heat removal of helium-xenon cooled nuclear reactor.

Neutronics and thermal-hydraulics coupling analysis using the FLUENT code and the RELAP5-3D code for a molten salt fast reactor

The present study proposes a method for analyzing the thermal hydraulics coupling with the neutron point kinetics of a molten salt fast reactor. First, it has been analyzed by the FLUENT code that the flow behaviors in the reactor under the steady state conditions are greatly influenced by the installation condition of the inlet piping. Among them, the case where the inlet pipes are not offset is selected as a representative case. Next, the method of coupling the neutronics and thermal-hydraulics using UDF of the FLUENT code is explained when a transient analysis is conducted. In the case of using the system code RELAP5-3D, it is explained that thermophysical property binary files of the molten salts are generated, and the kinetic parameters for the implemented point kinetics model are modified in consideration of the inflow and outflow of delayed neutron precursors. A ULOF event has been simulated by the FLUENT code and the RELAP5-3D code, and it has been confirmed that the short-term evolutions in the comparison of reactor power and outlet temperature by the two codes show similar trends. It has been confirmed that when all the pumps are tripped, the core average temperature increases and the negative temperature reactivity coefficient feedback reduces the reactor power to the decay heat level. An event of single pump trip is also calculated with two codes, and it has been confirmed that the molten salt fast reactor has self-control characteristics on the basis of the negative temperature reactivity coefficient.

Thermodynamic evaluation of hydrogen and electricity cogeneration coupled with very high temperature gas-cooled reactors

Hydrogen production using thermal energy, derived from nuclear reactor, can achieve large-scale hydrogen production and solve various energy problems. The concept of hydrogen and electricity cogeneration can realize the cascade and efficient utilization of high-temperature heat derive for very high temperature gas-cooled reactors (VHTRs). High-quality heat is used for the high-temperature processes of hydrogen production, and low-quality heat is used for the low-temperature processes of hydrogen production and power generation. In this study, two hydrogen and electricity cogeneration schemes (S1 and S2), based on the iodine-sulfur process, were proposed for a VHTR with the reactor outlet temperature of 950 °C. The thermodynamic analysis model was established for the hydrogen and electricity cogeneration. The energy and exergy analysis were conducted on two cogeneration systems. The energy analysis can reflect the overall performance of the systems, and the exergy analysis can reveal the weak parts of the systems. The analysis results show that the overall hydrogen and electricity efficiency of S1 is higher than that of S2, which are 43.6% and 39.2% at the hydrogen production rate of 100 mol/s, respectively. The steam generators is the components with the highest exergy loss coefficient, which are the key components for improving the system performance. This study presents a theoretical foundation for the subsequent optimization of hydrogen and electricity cogeneration coupled with VHTRs.

Kinetic modeling of thermal reactor in Claus process using CHEMKIN-PRO software

We reported a kinetic modeling of thermal reactor in Claus process using CHEMKIN-PRO software. Five hypothetical acid gases with different H2S and NH3 contents were selected and analyzed with a focus on the reaction kinetics occurring in thermal reactor. Modeling results revealed that temperature in thermal reactor initially increased due to the facile oxidation of H2S and NH3, after which it maintained a constant value due to the competing pyrolysis and S2 formation reactions. These patterns lead to equilibrium temperature and gas composition at the reactor outlet. At this point, the reactor outlet temperature and gas composition were greatly affected by the ratio of H2S/NH3 in the acid gases. Accordingly, the ratio of H2S/SO2 in the outlet gas flowing into the subsequent catalytic reactor of the Claus process was changed, necessitating an appropriate process operation. Based on these results, we suggest that the Claus process can be properly controlled by adjusting the air flow rate according to H2S/NH3 ratio. The results indicated that the ratio of H2S/SO2 in the outlet gas decreased with increasing air flow rate. It is expected that the Claus process efficiency can be improved by appropriately controlling the air flow rate in correspondence with H2S/NH3 ratio.

Special Section: Selected Papers From the Ninth International Symposium on Supercritical Water-Cooled Reactors

Special Section: Selected Papers From the Ninth International Symposium on Supercritical Water-Cooled Reactors

Multidimensional Modeling of Steam-Methane-Reforming-Based Fuel Processor for Hydrogen Production

We present a three-dimensional (3-D) steam-methane-reforming (SMR) model consisting of a steam-reforming (SR) reactor, water gas shift reactor, preferential oxidation reactor, catalytic burner, heat exchangers, and balance of plant components. The mass and energy balance equations are derived considering the kinetic expressions of various SMR reactions and implemented in the commercial computational fluid dynamics software program Fluent by employing user-defined functions. The 3-D SMR model is then applied to a 10-kW SR reformer geometry and simulated for comparison with in-house experimental data. The simulation results and the experimental data show good agreement, and the model accurately captures the experimental exhaust gas compositions and the reactor outlet temperatures. The proposed 3-D simulation tool for predicting various transport and chemical processes is highly desirable from the viewpoint of design and optimization of full-scale SMR-based fuel processors.

Combined cycles-coupled high-temperature and very high-temperature gas-cooled reactors: Part II – Engineering design

Next generation nuclear power plant concepts, such as the high-temperature and very high-temperature gas-cooled reactors, have significant potential for addressing ever growing energy needs, but their implementation must first overcome several engineering limitations. Accordingly, based on the theoretical optimization performed in the Part I of this study, the parameters of combined cycle-coupled high-temperature and very high-temperature gas-cooled reactors were evaluated with the consideration of current engineering limitations including the compressor pressure ratio, reactor inlet temperature, turbine blade cooling, main steam parameters, and exhaust humidity of the steam turbine. Four different combined cycles were then designed and compared with respect to these five parameters. The resulting design values were also compared to the theoretical optimization values in Part I of this paper, revealing that the ratio of the design value to the theoretical value decreased with increasing reactor outlet temperature. The comparison also suggested that the combined cycle-coupled very high-temperature gas-cooled reactor has significant potential, as its cycle efficiency could be further improved once the identified engineering restrictions are overcome.

Combined cycle-coupled high-temperature and very high-temperature gas-cooled reactors: Part I—Cycle optimization

Very high-temperature gas-cooled reactors (VHTRs) have attracted worldwide attention because of their multiple uses, which include hydrogen production and high-efficiency power generation. Efficient power conversion is a key to improving the competitiveness of VHTRs. The combined cycle is a cyclic form of energy cascade utilization that makes full use of the high-temperature heat source of VHTRs. In this paper, a theoretical optimization method of combined-cycle efficiency is proposed for combined cycle-coupled high-temperature gas-cooled reactors (HTGRs) and VHTRs without considering specific engineering constraints. Based on a total differential analysis combined with a numerical analysis, the multi-variable combined-cycle efficiency was reduced to a function of two key parameters: the reactor outlet temperature and the main steam pressure. The remaining parameters can be determined by optimization within the defined domain. The theoretical optimization method proposed in this paper is conceptually clear and solves the problems presented by the many variables involved in combined cycle-coupled HTGRs without a clear variable optimization strategy. The results of this study provide guidance for the theoretical analysis and parameter design of combined cycle-coupled VHTRs.

ANALYSIS OF SUPERCRITICAL CO2 CLOSED BRAYTON CYCLE APPLIED TO SMR

Supercritical CO2 Brayton cycle has been studied to be used as power conversion system in many fields because of its competitive efficiency and compact structure. When applied to nuclear power systems, cycle parameters that have direct effects on cycle performances will be restricted differently under different reactor designs. At the same time, the small reactor systems based on existing technology and experience in PWR, especially the Small Modular Reactor (SMR), have been favored owing to their advantages on safety, feasibility, and economic benefit. The focus of the present work is on the performances of recuperated S-CO2 Brayton cycle applied to small PWR systems that have a relatively low range of core outlet temperature below 330 oC. The calculation model is based on the laws of thermodynamics and the cycle performance were analyzed. The results show that the inlet parameters of compressor have obvious effects on cycle efficiency due to the radical change of CO2’s thermal physical properties near the critical point. With given reactor outlet temperature and recuperator effectiveness, the cycle efficiency reduces as the compressor inlet temperature rises from 32 to 40 oC. And there exists an optimal compressor inlet pressure to achieve maximum cycle efficiency. Furthermore, this optimal inlet pressure depends on the compressor inlet temperature. It will slightly increase and the maximum cycle efficiency will decrease at elevated compressor inlet temperature. Once the compressor inlet pressure exceeds the optimal value, the influence of compressor inlet temperature on cycle efficiency decreases to negligible. Pinch point is a key consideration for S-CO2 Brayton cycle. Promotion of the recuperator effectiveness can improve the cycle efficiency, but temperature difference at the cold end of recuperator ( ΔTc ) decreases at the same time. Thus the recuperator effectiveness and cycle efficiency has upper limitations to avoid the pinch point. Cycle efficiency shows two extremums according to compressor inlet pressure for given ΔTc . However, the latter situation is not suitable for practical engineering on account of internal pinch point. The results are helpful for the application of S-CO2 Brayton cycle in nuclear power system and provide a basis for subsequent experimental research.

The impact of emergency operating safety procedures on mitigation the nuclear thermal power plant severe accident

The most important public concerns is the safety of nuclear power reactors. It is extremely important to protect the public from the nuclear radiation exposure in the undesired case of a nuclear power plant (NPP) accident. The proper performance of the safety systems of nuclear power plants is one of the most highly important concerns which enhances the use of nuclear energy options. This research paper focuses on the response and performance of the emergency safety systems of a pressurized water reactor (PWR) during loss of coolant accident (LOCA) for a selected reference PWR. The simulation depicts the reactor behavior during hot leg loss of coolant accident event and the leakage area is 200 cm2. This was accomplished by modeling the PWR and the passive safety systems employed using PCTran code which is designed to describe the emergency core cooling system (ECCS) response and core behavior under severe accident conditions. The ECCSs are designed to cool down the reactor core and to prevent core damage. Results of the core temperature distribution, reactor coolant inlet and outlet temperatures, reactor coolant mass flow rate, and other parameters have been compared with the reference data and demonstrated to be in good agreement with each other. This study demonstrates that the PCTran model is capable of contributing to the process of safety analysis of the NPP.

(Solar) Mixed Reforming of Methane: Potential and Limits in Utilizing CO2 as Feedstock for Syngas Production—A Thermodynamic Analysis

The reforming of natural gas with steam and CO2 is commonly referred to as mixed reforming and considered a promising route to utilize CO2 in the production of synthetic fuels and base chemicals such as methanol. In the present study, the mixed reforming reaction is assessed regarding its potential to effectively utilize CO2 in such processes based on simple thermodynamic models. Requirements for the mixed reforming reactions based on process considerations are defined. These are the avoidance of carbon formation in the reactor, high conversion of the valuable inlet streams CH4 and CO2 as well as a suitable syngas composition for subsequent synthesis. The syngas composition is evaluated based on the module M = ( z H 2 − z CO 2 ) / ( z CO 2 + z CO ) , which should assume a value close to 2. A large number of different configurations regarding CO2/H2O/CH4 at the reactor inlet, operating pressure and outlet temperature are simulated and evaluated according to the defined requirements. The results show that the actual potential of the mixed reforming reaction to utilize CO2 as feedstock for fuels and methanol is limited to approximately 0.35 CO2/CH4, which is significantly lower than suggested in literature. At 900 °C and 7 bar at the reactor outlet, which is seen suitable for solar reforming, a ratio of H2O/CH4 of 1.4 can be set and the resulting value of M is 1.92 (CO2/CO/H2 = 0.07/0.4/1).

Techno-economic assessment of chemical looping reforming of natural gas for hydrogen production and power generation with integrated CO2 capture

The current study presents the techno-economic analysis of the CLR-CC process. The CLR-CC process comprises of chemical looping reforming (CLR) of Natural Gas, water gas shift, CO2 capture and compression, and combined cycle power plant. A 1-D phenomenological model was developed using MATLAB and is used to study the performance of CLR, whereas the remaining part of the process was analysed using commercial software tools like Aspen and Thermoflow. The effect of design conditions in CLR, mainly the air flowrate to the oxidation reactor, oxidation reactor outlet temperature and the steam flowrate to the fuel reactor of CLR, on the overall techno-economic performance of the CLR-CC process is reported. The CH4 conversion in CLR, net electrical efficiency, CO2 avoidance rate and the Levelised Cost of Electricity (LCOE) have been identified as techno-economic performance indicators. For the sensitivity study carried out in this study through 12 cases, the net electrical efficiency of the CLR-CC process varies between 40.0 and 43.4%, whereas the LCOE varies between 75.3 and 144.8 $/MWh, which is highly dependent on the fuel cost and process contingency rates.

A Design of Parameters with Supercritical Carbon Dioxide Brayton Cycle for CiADS

Recompression supercritical carbon dioxide (SCO2) Brayton Cycle for the Chinese Initiative Accelerator Driven System (CiADS) is taken into account, and flexible thermodynamic modeling method is presented. The influences of the key parameters on thermodynamic properties of SCO2 Brayton Cycle are discussed and the comparative analyses on genetic algorithm and pattern search algorithm are conducted. It is shown that the cycle parameters such as turbine inlet temperature, pressure ratio, outlet temperature at the hot end of condenser, and terminal temperature difference of regenerator 1 and regenerator 2 have significant effects on the cycle thermal efficiency. The calculation results indicate that pattern search algorithm has better optimization performance and quicker calculating speed than genetic algorithm. The result of optimization of the parameters for CiADS with supercritical carbon dioxide Brayton Cycle is 35.97%. Compared with other nuclear power plants of SCO2 Brayton Cycle, CiADS with SCO2 Brayton Cycle does not have the best thermal efficiency, but the thermal efficiency can be improved with the reactor outlet temperature increases.

Combined cycle schemes coupled with a Very High Temperature gas-cooled reactor

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/VHTRs). In this paper, physical and mathematical models of two combined cycle schemes coupled with the VHTR, Reheated Combined Cycle (RCC) and Regenerative-Reheated Combined Cycle (RRCC), are established. Their topping cycle is a no precooling and no intercooling Brayton cycle, and their bottoming cycle is a supercritical Rankine cycle. The effects and mechanism of key parameters were analyzed. Based on parameter analysis, two schemes were compared within the temperature range of the VHTRs (ROT 950–1200 °C). The analysis shows that, for the combined cycle of the VHTR, by adding a recuperator, can further utilize the helium turbine exhaust heat, then to improve the cycle efficiency. When the ROT is 1050 °C, the cycle efficiency of the RRCC (recuperator's effectiveness 0.4）is 56.4%, which is 2.18% higher than that of the RCC. But because of the regenerative process, the reactor inlet temperature (RIT) of the RRCC is higher than 490 °C, additional reactor pressure vessel (RPV) cooling system is necessary, and it increases the system complexity and reduce the cycle's efficiency. The RIT of the RCC can be controlled below 490 °C, no RPV cooling system is required. Amongst the main parameters, the recuperator's effectiveness and compression ratio are the most important factor affecting the cycle efficiency of the VHTR. The cycle efficiency can be increased by 0.61% when the recuperator's effectiveness is increased by 0.1. The main factors that limit the increase of the recuperator's effectiveness are the RIT and the system flow resistance. When the average compression ratio increases by 0.1, the combined cycle efficiency increases by 0.33% (RCC) and 0.373% (RRCC). The main factors that limit the increase of compression ratio are the manufacturing capacity of magnetic bearings, turbines and compressors. These results provide insights on the combined cycle of the VHTRs, 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 VHTR in the future.

Cooling Performance Analysis of ThePrimary Cooling System ReactorTRIGA-2000Bandung

The conversion of reactor fuel type will affect the heat transfer process resulting from the reactor core to the cooling system. This conversion resulted in changes to the cooling system performance and parameters of operation and design of key components of the reactor coolant system, especially the primary cooling system. The calculation of the operating parameters of the primary cooling system of the reactor TRIGA 2000 Bandung is done using ChemCad Package 6.1.4. The calculation of the operating parameters of the cooling system is based on mass and energy balance in each coolant flow path and unit components. Output calculation is the temperature, pressure and flow rate of the coolant used in the cooling process. The results of a simulation of the performance of the primary cooling system indicate that if the primary cooling system operates with a single pump or coolant mass flow rate of 60 kg/s, it will obtain the reactor inlet and outlet temperature respectively 32.2 °C and 40.2 °C. But if it operates with two pumps with a capacity of 75% or coolant mass flow rate of 90 kg/s, the obtained reactor inlet, and outlet temperature respectively 32.9 °C and 38.2 °C. Both models are qualified as a primary coolant for the primary coolant temperature is still below the permitted limit is 49.0 °C.

A control approach investigation of the Xe-100 plant to perform load following within the operational range of 100 – 25 – 100%

This paper describes the Xe-100 plant load following analyses done in Flownex® thermal-fluid system simulation software for normal operation from 100 – 25 – 100% electrical power. The plant model encompasses all major components in the Xe-100 plant’s primary helium side including the pebble bed reactor, helium circulator, and steam generator, which transfers heat to the secondary steam side feeding steam to a steam-turbine in the Rankine cycle. The requirement for load following was to have a ramp rate of 5% per minute when the turbine-generator power level ramps down from full power to 25% power level and back to full power. The control approach, which pairs selected manipulated variables namely the: reactor control rods; helium circulator speed; feed water pump speed; turbine throttle valve to selected controlled variables namely the: reactor outlet temperature; main steam temperature; main steam pressure; turbine-generator power, is discussed in this paper. The controller actions on the manipulated variables and their response during the load following signal are illustrated. The deviation of the controlled variables during load following are shown within their required limits. This paper shows that the Xe-100 plant can achieve a 100 – 25 – 100% electrical load ramp at a rate of 5% per minute.

Energy, exergy and exergoeconomic analyses of a combined supercritical CO2 recompression Brayton/absorption refrigeration cycle

Exergoeconomic analysis is performed for a novel combined SCRB/ARC (supercritical CO2 recompression Brayton/absorption refrigeration cycle) in which the waste heat from the SCRBC is recovered by an ARC for producing cooling. Parametric analysis is conducted to investigate the effects of the decision variables on the performance of the SCRB/ARC cycle. The performances of the SCRB/ARC and SCRBC cycles are optimized and compared from the viewpoints of first law, second law and exergoeconomics. It is concluded that combining the SCRBC with an ARC can not only enhance the first and second law efficiencies of the SCRBC, but also improve the exergoeconomic performance. The results show that the largest exergy destruction rate occurs in the reactor, while the components in the ARC have less exergy destruction. The reactor and turbine are the first and second important components from exergoeconomic aspects. When optimization is based on the exergoeconomics, the first and second law efficiencies and the total product unit cost of SCRB/ARC are 26.12% higher, 2.73% higher and 2.03% lower than those of the SCRBC. The optimization study also reveals that an increase in the reactor outlet temperature can enhance both thermodynamic and exergoeconomic performances of the SCRB/ARC. For the basic design case, the SCRB/ARC can produce 71.76MW of the cooling capacity and 6.57MW of the cooling exergy at the expense of only 0.36MW of power in comparison with the SCRBC.