High-temperature Reactor Research Articles

Design and optimization of thermal insulation structure for high-temperature pipeline inside the lower tank wall

The operating temperature of the high-temperature pipeline running through the lower tank of a high temperature reactor is relatively high, while the temperature limit of the wall material is relatively low, thus thermal insulation design of high-temperature pipeline is required. Simulated the temperature field of the lower tank wall insulation structure, and compared with the experimental data to verify the accuracy of the model. On the basis of the initial scheme, the structural load was reduced by the introduction of heat pipes. When 10 heat pipes were arranged, the thickness of the carbon steel layer in the thermal insulation design could be reduced from 10 cm to 3 cm or less, and the failure of some heat pipes would not cause the local temperature of the wall material to exceed the limit. This is an innovative thermal insulation and heat conduction design for high-temperature pipeline penetrating the tank wall.

Ammonia energy storage for hybrid electric aircraft

This work considers the development of a hybrid electric vertical takeoff and landing aircraft with an NH3 engine. An NH3 cracker with an external heat supply from the engine and a high-temperature catalytic reactor is needed to crack part of the NH3 in H2 and N2. The engine has two turbochargers in cascade, an intercooler, and an SCR catalyst with additional NH3 injection before the catalyst to control emissions. The H2 is used to ignite an NH3 mixture which may also be enriched with hydrogen to address particularly slow-burning points. The proposed learn burn engine which features direct injection and jet ignition of H2 may have power densities above 100 kW per liter and fuel conversion efficiencies approaching 50%. This engine can be further specialized to work on a narrow range of speeds and loads, ideally, one single point, to produce electricity on board the aircraft. The energy storage per unit mass of the complete system is expected to reduce vs. diesel but not dramatically. Importantly, it is much better than the storage of energy in a battery.

Dechlorination and fuel gas generation in chemical looping conversion of waste PVC over inherently Na/Ca/K-containing bauxite residue-based oxygen carriers

The inert atmosphere in chemical looping (CL) technology can considerably inhibit the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during the thermal treatment of polyvinyl chloride plastic (PVC) waste. In this study, PVC was innovatively converted to dechlorinated fuel gas via CL gasification under a high reaction temperature (RT) and the inert atmosphere by applying an unmodified bauxite residue (BR) as both a dechlorination agent and oxygen carrier. The dechlorination efficiency reached 49.98% at an oxygen ratio of only 0.1. Furthermore, a moderate RT (750 °C in this study) and an increased oxygen ratio enhanced the dechlorination effect. The highest dechlorination efficiency (92.12%) was achieved at an oxygen ratio of 0.6. Iron oxides in BR improved the generation of syngas from CL reactions. The yields of the effective gases (CH4, H2, and CO) increased by 57.13% to 0.121 Nm3/kg with an increase in oxygen ratio from 0 to 0.6. A high RT improved the production of the effective gases (an 809.39% increase to 0.344 Nm3/kg from 600 to 900 °C). Energy-dispersive spectroscopy and X-ray diffraction were used to study the mechanism, and formation of NaCl and Fe3O4 was observed on the reacted BR, indicating the successful adsorption of Cl and its capability as an oxygen carrier. Therefore, BR eliminated Cl in situ and enhanced the generation of value-added syngas, thereby achieving efficient PVC conversion.

Evolution of the microstructure of superfine grain graphites under thermal oxidation

Nuclear graphite is used as a moderator and structural material in a number of Gen-IV reactor designs, such as the (Very) High Temperature Reactors. Chronic or acute thermal oxidation affects the mechanical properties of the graphite components and the impact on the structural integrity of the core depends on the evolution of the microstructure during oxidation.This study qualitatively examined the microstructure of four superfine grain graphites using polarised and fluorescent optical microscopy. These graphites had similar physical properties but notable differences in the oxidation rate at 700 °C. Using fluorescent microscopy, it was possible to distinguish between open and closed porosity in graphite, which is useful in understanding the progression of thermal oxidation and penetration depth. Based on the samples in this work, fine open and closed porosity may be linked to increased surface oxidation and relatively high oxidation rate, whereas high penetration depth may be linked to relatively low open porosity consisting mainly of large pores. Fairly large domains of coherent crystallite orientation, perhaps due to the presence of agglomerates, may also indicate lower oxidation rates at 700 °C.This paper demonstrated that fluorescent microscopy combined with image analysis, is a useful tool in understanding the progression of thermal oxidation and the corresponding effect on the microstructure.

Effect of Oxygen Ion Irradiation on Nb-1Zr-0.1C Alloy Characterized Using X-Ray Diffraction Line Profile Analysis

One of the proposed materials for structural application in compact high-temperature reactors (CHTRs) is Nb-1Zr-0.1C alloy. Using the Variable Energy Cyclotron at the Variable Energy Cyclotron Centre, Kolkata, Nb-1Zr-0.1C alloy was irradiated with a 160-MeV oxygen (O6+) ion up to three different doses. Emulation of neutron irradiation by ion irradiation could be achieved as the weighted recoil spectra of the oxygen ion are found to be similar to the neutron recoil spectra of CHTRs within recoil energy ranging from 100 eV to 100 keV. The irradiated materials along with one as-received sample were characterized using different X-ray diffraction line profile analyses (XRDLPAs) to systematically evaluate microstructural parameters. A decrease in the domain size with an increase in microstrain and dislocation density is observed at first dose and then found to saturate with further irradiation. An increase in the Wilkens arrangement parameter indicates the formation of less correlated dislocations (clusters) after irradiation. Transmission electron microscopy analysis of as-received and highest-dose samples shows the formation of densely populated defect clusters after irradiation. Nanohardness increased after irradiation due to pinning of the dislocation movement by point defects and defect clusters/loops, as well as carbides in the matrix. The results extracted from the XRDLPAs are compared with our earlier studies of light ion–irradiated (H+) Nb-1Zr-0.1C alloy and oxygen-irradiated pure Nb to understand the effect of the type of ion and the alloying elements, respectively, on the evolution of the microstructure. It may be concluded that changes in dose and dose rate affect the movement of point defects toward sinks. Hence, possible correlated dislocation formation is observed in light ion–irradiated Nb alloy, but correlation is found to decrease with dose for heavy ion–irradiated Nb alloy. On the other hand, the presence of finely dispersed carbides restricts the formation of dislocation loops by making complexes with the defects in heavy ion (O6+)–irradiated Nb-1Zr-0.1C alloy, which is in contrast to pure Nb irradiated using the heavy ion (O6+) in a similar environment.

Dl-Methionine-Mediated Reversible Deactivation Radical Polymerization of Styrene and Methyl Methacrylate.

Reversible deactivation radical polymerization (RDRP) is a facile and highly efficient technique for the synthesis of well-defined polymer with precise structure. dl-Methionine (Met) as a RDRP control agent is described and assessed for RDRP of styrene (St) and methyl methacrylate (MMA) with AIBN as radical initiator at 75°C, which enables excellent control of this polymerization. The addition of dl-Methionine significantly decreased the dispersity (Đ) of the polymers for both monomers and first-order linear kinetic plots of polymethyl methacrylate (PMMA) are observed in DMSO. Considering the heat resistance of dl-Methionine, kinetic studies indicate that polymerization develops at a faster rate at higher reaction temperature (100°C) with the same dl-Methionine content. Well-defined polymethyl methacrylate-block-polystyrene (PMMA-block-PSt) is successfully achieved by the chain extension reaction that demonstrates the high end fidelities of this polymerization approach. The system allows the use of dl-Methionine, a rich source and easily synthesized agent, to mediate RDRP strategy.

Boosting Methanol-Mediated CO2 Hydrogenation into Aromatics by Synergistically Tailoring Oxygen Vacancy and Acid Site Properties of Multifunctional Catalyst.

Even though the direct hydrogenation of CO2 into aromatics has been realized via a methanol-mediated pathway and multifunctional catalyst, few works have been focused on the simultaneously rational design of each component in multifunctional catalyst to improve the performance. Also, the structure-function relationship between aromatics synthesis performance and the different catalytic components (reducible metal oxide and acidic zeolite) has been rarely investigated. Herein, we increase the oxygen vacancy (Ov ) density in reducible Cr2 O3 by sequential carbonization and oxidation (SCO) treatments of Cr-based metal-organic frameworks. Thanks to the enriched Ov , Cr2 O3 -based catalyst affords high methanol selectivity of 98.1 % (without CO) at a CO2 conversion of 16.8 % under high reaction temperature (350 °C). Furthermore, after combining with the acidic zeolite H-ZSM-5, the multifunctional catalyst realizes the direct conversion of CO2 into aromatics with conversion and selectivity as high as 25.4 % and 80.1 % (without CO), respectively. The property of acid site in H-ZSM-5, especially the Al species that located at the intersection of straight and sinusoidal channels, plays a vital role in enhancing the aromatics selectivity, which can be precisely controlled by varying the hydrothermal synthesis conditions. Our work provides a synergistic strategy to boost the aromatics synthesis performance from CO2 hydrogenation.

Study on iterative algorithm of full plate cross-flow and counter-flow printed circuit heat exchanger for fluoride-salt-cooled high-temperature advanced reactor

In the concept of Fluoride-Salt-cooled high-Temperature Advanced Reactor (FuSTAR), the Printed Circuit Heat Exchanger (PCHE) is mainly considered in its supercritical carbon dioxide (S–CO2) Brayton cycle secondary loop. The design of the PCHE is based on the property of working fluid provided by the Brayton cycle system design. Therefore, a fast and iterative PCHE design method is required. In this study, a mathematical model based on Picard's iterative method is proposed. The model can solve full plate temperature field with complex boundary conditions and initial values including cross-flow and counter-flow PCHE in parallel. Based on FuSTAR Brayton cycle design conditions, three sizes of cross-flow and counter-flow PCHEs are simulated respectively by the mathematical model. Compared with Computational Fluid Dynamics (CFD) models, a one and three-dimensional coupling model and a three-dimensional model, the mathematical model reduced the computing time from 1 to 10 h to 1–10 s, and the maximum temperature mean deviation is 18.6% for the smallest size case because of the edge effect and local disturbance, but 8.4% for other size. Taking secondary loop recuperator design as example, the computing speed and accuracy of the mathematical model can meet the design requirements of FuSTAR PCHE.

Comparison of Melted Corium Relocation during Severe Accident of High Temperature Reactor using Moving Particle Semi-Implicit Method

System failure in nuclear reactors can cause degradation of a reactor core, allowing melting and relocation of the corium to the lower plenum in the nuclear reactor system. In this study, a severe accident simulation was carried out using the Moving Particle Semi-Implicit (MPS) method. In this method, we model the relocation of molten corium on the reactor core (support plate) to the lower plenum for several conditions with variations: corium material, lower plenum conditions, temperature, viscosity, and density. Those treatments were carried out in order to be able to compare and analyze the characteristics of the corium melt by reviewing the velocity profiles. The formation of a corium pool and debris bed can result in significant temperature differences and high heat flux against the walls of the reactor vessel, causing a decrease in the integrity of the reactor vessel and reactor failure.Keywords: Corium, Uranium Dioxide (UO2), Zirconium Dioxide (ZrO2), Fluid Relocation, Moving Particle Semi-Implicit (MPS).

Characterization of the oxide film and deuterium permeation behavior of CoCrMnFeNi high entropy alloy oxidized at 550 ℃ for 24 h

High entropy alloys have become potential candidate materials for high temperature nuclear reactor due to its high strength, high hardness, excellent corrosion resistance and radiation resistance, therefore the compatibility of hydrogen isotopes with HEAs becomes a key issue that has attracted a lot of attentions. The deuterium permeation behavior of the CoCrMnFeNi high entropy alloy after oxidation at 550 °C for 24 h was investigated by gas-phase deuterium permeation testing, SEM, X-ray diffraction methods in this paper. The results show that an oxide film with a thickness of about 1 μm was formed on the surface of the sample after oxidation. The outer layer of the oxide film is rich in Mn2O3 and the inner layer is rich in Cr2O3. The deuterium permeability of the CoCrMnFeNi sample after oxidation was reduced by an order of magnitude and was 1/7–1/17 times as high as that for the unoxidized one.

Assessing the efficiency of CO2 hydrogenation for emission reduction: Simulating ethanol synthesis process as a case study

Hydrogenation of CO2 to synthesize ethanol is a potential way to reduce CO2 emissions while producing value-added fuels and chemicals. However, the emission of tail gas as well as the consumption of heat and electricity may also generate additional CO2 emissions. This raises the question of how efficient this process is in reducing CO2 emissions. In this study, Aspen Plus is used to investigate the efficiency of this process towards reduction of CO2 emission. The effect of key parameters such as single pass CO2 conversion, tail gas splitting ratio, and reaction temperature on CO2 conversion efficiency, hot utility/electricity consumption, as well as CO2 emission reduction/utilization rate is examined. It is recommended that a medium single pass conversion (e.g., 15%), a high splitting ratio (e.g., 0.8), and a relatively high reaction temperature (e.g., 250 ℃) for practical applications of this technology. With an annual CO2 processing capacity of 268 kt, our study suggests that up to 86.9% of CO2 emissions can be eliminated, resulting in the production of 141 kt/year of ethanol, demonstrating the high efficiency of this process in reducing CO2 emissions.

Fractographic studies and tensile strength of MPG-6 graphite based on uncalcined coke, neutron-irradiated at a high temperature

This paper presents the results of studies of the mechanical properties and fracture characteristics of MPG-6 graphite in the unirradiated state and neutron-irradiated at high temperature. MPG-6 is considered as a material for future high-temperature gas-cooled reactors (HTGR). In particular, MPG-6 is considered as one of the candidate materials for prismatic fuel blocks of the Russian experimental hydrogen-producing nuclear power plant with the VTGR high-temperature reactor currently under design.It is shown that MPG-6 graphite, based on uncalcined petroleum coke, which causes a small difference in the size of crystallites in areas with different preferred orientations of crystallites, has higher radiation stability of mechanical properties than GR-280 graphite based on calcined coke.

Heating-free synthesis of red emissive carbon dots through separated processes of polymerization and carbonization

Polymerization and carbonization are believed as two basic processes for the bottom-up synthesis of carbon dots (CDs). Since these two processes usually occur simultaneously due to the high reaction temperature and fast reaction rate, it is still a challenge to separate and control these two processes. In the present work, we reported a new room temperature method, which achieved the separated and controlled polymerization and carbonization processes. The polymerization process is realized by dissolving o-phenylenediamine (OPD) in ethanol at room temperature, and finally obtained polymer dots (PDs) without any lattice with a sphere size of 29.6 nm. The carbonization process begins in a manual way by adding concentrated sulfuric acid. After carbonization, CDs (noted as CPDs in this work) with a size of 3.6 nm and a clear lattice can be obtained. Importantly, the separated polymerization and carbonization make us possible to adjust the composition or interactions of intermediate products during the synthesis process. As a prototype, we added acetic acid (AA) additives into OPD precursors during the polymerization stage. Due to the crosslink enhanced emission (CEE) effect via hydrogen bonds which are produced by the amide groups from AA reaction products with H in the –NH3+ or aromatic ring, the resulted CPDs show improved PLQY from an initial 6.87% (without AA) to 16.47%. The current work realized the separated and controllable polymerization and carbonization processes, opening up the door for tuning the composition and interactions of intermediate products before carbonization.

Diffusion study of uranium mononitride/zirconium carbide composite for space nuclear propulsion

The next generation of space exploration will require extensive developments in rocket technology. Space nuclear propulsion is of interest due to its high fuel density and power; however, it also has high temperature and stability demands. This study examines a uranium mononitride (UN) and zirconium carbide (ZrC) ceramic-ceramic particle composite as a potential fuel for these missions. Based on the constituent properties, this fuel composite is expected to be thermally efficient and resistant to the hot hydrogen propellant. One of the main concerns with this composite is the unknown diffusion behavior between UN and ZrC over time. Diffusion couple experiments and isothermal furnace tests of composites were two experimental techniques used to determine how these constituents will behave when left in contact at high temperatures. UN and ZrC were found to have limited but observable diffusion at the phase boundary. The resulting phase is a UZr(CN) quaternary phase. UZr(CN) has been examined for other high temperature and gas nuclear reactors with preliminary success; however, there lacks sufficient data to fully understand this phase. Based on the limited information available, the resultant quaternary phase could be deemed acceptable and even provide better adhesion for the fuel particles (UN) to the matrix (ZrC).

Study on the mechanisms of hydrogen production from alkali lignin gasification in supercritical water by ReaxFF molecular dynamics simulation

Lignin is a major polymer in the black liquor of paper mill and one of the most important components of biomass. Supercritical water gasification (SCWG) technology, which is an efficient and clean method for waste lignin treatment, has a good application prospect. To improve the conversion efficiency of lignin, it is necessary to reveal the detail mechanisms of lignin gasification in supercritical water (SCW). Based on the actual molecular structure of lignin, a model of complex lignin was constructed by using Materials Studio (MS). The effects of different reaction parameters on gasification results were analyzed with the reactive force field molecular dynamics method (ReaxFF MD). The simulation results show that higher reaction temperature and lower reactant concentration lead to higher efficiency of lignin gasification in SCW, and lignin has the highest gasification efficiency at 3500 K and 15 wt%. Additionally, the decomposition pathway of lignin and the generation paths of CO2, H2 were clarified. This work will provide theoretical guidance for further research to improve the SCWG efficiency of lignin.

A Consistent Low-Order Acceleration Technique for Coarse Mesh Transport (COMET) Methods

The COarse MEsh Transport (COMET) method, a hybrid continuous energy stochastic and deterministic transport method/tool based on the incident flux response expansion theory, is capable of providing highly accurate and efficient continuous energy whole-core neutron solutions to various heterogeneous reactor cores. In this work, a novel low-order (zeroth-order) acceleration technique is developed to significantly improve COMET’s computational efficiency for core calculations. This new method is based on consistent coupled low-order and high-order calculations to obtain the COMET core solution. In the low-order calculations, COMET is used to converge the total partial current escaping from each coarse mesh and the core eigenvalue. The resulting fixed-source problem in which the off-diagonal terms (equivalent to the scattering and fission neutron sources) are constructed by the zeroth-order solution are efficiently solved by the high-order COMET calculations. The resulting high-order angular flux on each coarse mesh bounding surface is then used to update (collapse) the low-order response coefficients. The coupled low-order and high-order calculations are repeated until both the eigenvalue and the low-order response coefficients are converged. The new acceleration method is implemented into COMET and tested in a set of stylized Advanced High Temperature Reactor (AHTR) benchmark problems. It is found that the core eigenvalues and the local fission density distributions predicted by COMET with the low-order acceleration agree very well with those computed by the original COMET. The eigenvalue discrepancy varies from 0 to 1 pcm, and the average relative differences in the stripewise and assembly-average fission density distributions are in the range of 0.021% to 0.032% and 0.004% to 0.01%, respectively. The comparisons have shown that the new low-order acceleration method can maintain COMET’s accuracy while improving its computational efficiency for core calculations by 12 to 16 times.

Experimental Performance of a Nonlinear Control Strategy to Regulate Temperature of a High-Temperature Solar Reactor

Abstract Despite the significant potential of solar thermochemical process technology for storing solar energy as solid-state solar fuel, several challenges have made its industrial application difficult. It is important to note that solar energy has a transient nature that causes instability and reduces process efficiency. Therefore, it is crucial to implement a robust control system to regulate the process temperature and tackle the shortage of incoming solar energy during cloudy weather. In our previous works, different model-based control strategies were developed namely a proportional integral derivative controller (PID) with gain scheduling and adaptive model predictive control (MPC). These methods were tested numerically to regulate the temperature inside a high-temperature tubular solar reactor. In this work, the proposed control strategies were experimentally tested under various operation conditions. The controllers were challenged to track different setpoints (500 °C, 1000 °C, and 1450 °C) with different amounts of gas/particle flowrates. Additionally, the flow controller was tested to regulate the reactor temperature under a cloudy weather scenario. The ultimate goal was to produce 5 kg of reduced solar fuel magnesium manganese oxide (MgMn2O4) successfully, and the controllers were able to track the required process temperature and reject disturbances despite the system's strong nonlinearity. The experimental results showed a maximum error in the temperature setpoint of less than 0.5% (6 °C), and the MPC controller demonstrated superior performance in reducing the control effort and rejecting disturbances.

Visible Light-Driven Sandwich-like g-C3N4-Catalyzed Oxidation to Produce Cumene Hydroperoxide

Cumene hydroperoxide (CHP) is an important intermediate for the production of phenol, acetone, propylene oxide, and other raw materials in the petrochemical industry. However, due to the high reaction temperature and pressure, the current process for the industrial production of CHP has problems of potential safety hazards and high energy consumption. In this work, carbon nitride (g-C3N4) with a unique sandwich structure was discovered as a photocatalyst. It efficiently activates molecular oxygen in the air, oxidizes cumene (CM) to prepare CHP, and realizes high atom economy transformation at room temperature, atmospheric pressure, and solvent-free conditions. The continuous flow strategy was adopted to improve the gas–liquid mass transfer efficiency and reduce the phenomenon of back-mixing, thereby reducing the decomposition of the products and improving the product selectivity. The conversion rate was the same as that of the batch reaction, reaching 23%. The selectivity of the product CHP increased from 82 to 92%, and the reaction residence time was shortened from 10 h to 70 min. The catalysts have the advantages of high efficiency, easy availability, environmentally friendly, etc., and are recyclable and stable. This work provides a new strategy for establishing green, sustainable, clean, and efficient methods for the preparation of peroxides.

Statistical evaluation of the epoxidation of esters from vegetable oils and optimization of reaction conditions

The increasing glycerol consumption will result in an issue for further applications of methyl esters, which are produced together with glycerol by transesterification of vegetable oils/animal fats on industrial scale. One possibility is the formation of bio-epoxides, which can be used for bio-lubricants, precursors for chemicals or CO2 capture, and so they can replace products from crude oil. Therefore, the mathematical models describing epoxidation of methyl esters, i.e., the influence of reaction conditions (time, temperature, etc.) on the properties of epoxides (iodine and epoxide values, relative conversion to oxirane, etc.) were created/calculated to decrease the production cost. It was found that (i) higher initial iodine value of esters, (ii) higher reaction temperature, (iii) higher concentration of formic acid and (iv) longer reaction time caused more formed epoxides. In contrast, a higher concentration of hydrogen peroxide caused epoxide ring opening and the formation of side products. The catalyst (H2SO4) and the intensity of stirring were statistically insignificant. The drying of epoxides was carried out by distillation and improved by the addition of a small amount of methanol. The models allow the synthesis of epoxides with desired properties, which are biodegradable and nontoxic with variety of applications.

High-temperature reactivity of vanadium oxide clusters in methane activation: Vibrational degrees of freedom matter.

Understanding the properties of small particles working under high-temperature conditions at the atomistic scale is imperative for exact control of related processes, but it is quite challenging to achieve experimentally. Herein, benefitting from state-of-the-art mass spectrometry and by using our newly designed high-temperature reactor, the activity of atomically precise particles of negatively charged vanadium oxide clusters toward hydrogen atom abstraction (HAA) from methane, the most stable alkane molecule, has been measured at elevated temperatures up to 873K. We discovered the positive correlation between the reaction rate and cluster size that larger clusters possessing greater vibrational degrees of freedom can carry more vibrational energies to enhance the HAA reactivity at high temperature, in contrast with the electronic and geometric issues that control the activity at room temperature. This finding opens up a new dimension, vibrational degrees of freedom, for the simulation or design of particle reactions under high-temperature conditions.