Thermal Reactor Systems Research Articles

Regulated Formation of Inhibited Color and Enhanced Flavor Derived from Heated 2-Threityl-Thiazolidine-4-Carboxylic Acid with Additional Cysteine Targeting at Different Degradation Stages.

This study explored the addition of cysteine (Cys) affecting the color formation of heated 2-threityl-thiazolidine-4-carboxylic acid (TTCA) models under different reaction conditions and pointed out that temperature was considered to be the key parameter influencing the color inhibition behavior of Cys on TTCA reaction models. Results revealed that additional Cys not only controlled the reaction progress and blocked the formation pathway of browning but also changed the formation rate, intensity, and profile of the flavor generated from the TTCA reaction model. Meanwhile, the mechanism of Cys simultaneously regulating the formation of color and flavor was revealed through monitoring of the characteristic downstream products during TTCA degradation and model reaction systems. At the initial stage, the additional Cys acted as a color inhibitor before the deoxyxylosone degradation, preventing the formation of downstream browning precursors. With the continuous depletion of Cys as well as the generation of furans or α-dicarbonyl compounds, Cys became a flavor enhancer to act on the browning precursors and to provide more sulfur/nitrogen elements for the TTCA thermal reaction system. Therefore, Cys had the potential to act as both color inhibitor and flavor fortifier to match with TTCA for the preparation of a light-colored flavoring base with a desired flavor during thermal processing.

Relationship between olefins and coking propensity of heavy residual oil derived from vacuum residue thermal cracking products

Olefins, especially olefinic-bond-containing aromatics (OAH) may have a significant effect on the coking propensity of heavy residual oil (RO) derived from vacuum residue (VR) thermal cracking products in the further deep processing. However, this has been rarely studied in the past. In this work, the structure of RO (boiling point > 500 °C distillate) products and their SARA fractions derived from thermal cracking of VR under different conditions were systematically characterized by 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) spectroscopy to investigate the occurrence pattern of olefins. The coking propensity of RO in the further processing was evaluated by thermal gravimetric (TG) and coking factor analysis, and the effect of different olefins on the coking propensity of RO in further processing was revealed. The results showed that the thermal cracking led to the occurrence of olefins, especially OAHs in resins (Re) and asphaltenes (Asp). The highest olefinic hydrogen contents of RO and its SARA fractions were detected at the thermal cracking condition of 415 °C for 40 min, which were 2.9 %, 4.0 %, 3.4 %, 2.8 %, and 2.4 %, respectively. Interestingly, RO obtained at the thermal cracking condition of 415 °C for 40 min also had the highest content of TG carbon residue (11.2 wt%) and the largest value of coking factor (5.33 %). Significantly, the TG carbon residue content and coking factor value of RO linearly increased with the total olefinic hydrogen content of RO, suggesting that the occurrence of olefins during thermal cracking significantly contributed to a greater coking propensity of RO in further deep processing. More importantly, an in-depth investigation by adding different olefin model compounds to the original VR thermal reaction system revealed that the olefinic-bond-containing aromatics in Asp may confer the greatest contribution to the increasing coking propensity of RO, followed by the olefinic-bond-containing aromatics in Re.

Evidence of Kinetically Relevant Consistency in Thermal and Photo-Thermal HCOOH Decomposition over Pd/LaCrO3 /C3 N4 Composite.

Photo-thermal catalysis has been an attractive alternative strategy to promote chemical reactions for years, however, how light cooperates with thermal energy is still unclear. We meet this demand by exploring reaction mechanism via pressure dependency studies as well as H/D exchange experiments with HCOOH decomposition as a probe over a palladium nanoparticle (Pdn ) and isolated Pd (Pd1 ) decorated LaCrO3 /C3 N4 composite catalyst, in which the H2 formation rate shows a first-order dependence on HCOOH and inverse first-order dependence on CO partial pressures no matter the reaction was driven by thermal or photo-thermal energy. Additionally, negligible kinetic isotopic effects (KIEs: kH /kD ) were determined under both dark and light conditions at 1.04 and 1.18 when the HCOOH was replaced by HCOOD. Besides, when the reactant HCOOH was further replaced by DCOOD, the KIE values of 1.55 (dark) and 1.92 (light) were obtained, which indicates that the HCOOH decomposition follows kinetically relevant (KR) of C-H bond rupture within HCOOH molecule under both thermal and photo-thermal reaction conditions and the catalytic surface was found to be densely covered by CO based on the pressure dependency studies as well as the in situ Fourier transform infrared spectroscopy (FTIR) analysis. Clearly, the HCOOH decomposition driven by thermal and photo-thermal energy follows the same reaction mechanism. Nevertheless, light induced hot electrons and the derived thermal effect do cause the enhancement of the reaction activity in some circumstances compared with bare thermal catalysis, which clarifies the confusion on cooperation mechanism of photo and thermal energies from the kinetic perspective. Hot electrons induced by photo-illumination was confirmed by in situ FTIR CO chemisorption with ∼10 cm-1 redshift identified of the CO feature once light was introduced. Meanwhile, the photo thermal reaction system suffers from severe electron-hole re-combination at high reaction temperatures and make the thermal effect of photo irradiation dominant with respect to the effect at low reaction temperatures. This research provides insight to the mechanism on how photo-thermal reaction works and draws attention to the photo-thermal reaction process in boosting catalytic activity.

Applicability of several Feynman-α formulae to a subcritical thermal reactor

ABSTRACT For an university training and research reactor of Kindai University, the Feynman-α analyses based on several formulae are carried out to examine the applicability of these formulae to the subcritical thermal reactor system. The original formula, in which the effect of delayed neutrons is neglected, results in a prompt-neutron decay constant sensitive to an upper limit of the gate time range of the analysis and consequently has difficulty in determining the decay constant. This difficulty originates from the neglect of delayed neutrons. An improved formula, where a term proportional to the gate time is added to the original formula, gives a desirable decay constant insensitive to the upper limit and the insensitive decay constant well agrees with that obtained from the Rossi-α analysis. The application of a difference filtering technique also leads to a successful result similar to the above improved formula. An alternative index Z to the traditional index Y of the original formula has been sometimes employed as an indication of the non-Poisson nature of the counting statistics. The Z is defined as dividing the Y by the mean number of neutron counts accumulated in the gate time. The formula for the Z never results in a reasonable decay constant even though the effect of delayed neutrons is considered. This study suggests that the improved formula considering delayed neutrons for the Y and the formula for the difference filtering technique should be employed to determine the prompt-neutron decay constant of thermal reactors.

IMPROVEMENT OF SCALE-XSProc MULTIGROUP CROSS SECTION PROCESSING BASED ON THE CENTRM POINTWISE SLOWING DOWN CALCULATION

The SCALE-XSProc multigroup (MG) cross section processing procedure based on the CENTRM pointwise slowing down calculation is the primary procedure to process problem-dependent self-shielded MG cross sections and scattering matrices for neutron transport calculations. This procedure supports various cell-based geometries including slab, 1-D cylindrical, 1-D spherical and 2-D rectangular configurations and doubly heterogeneous particulate fuels. Recently, this procedure has been significantly improved to be applied to any advanced reactor analysis covering thermal and fast reactor systems, and to be comparable to continuous energy (CE) Monte Carlo calculations. Some reactivity bias and reaction rate differences have been observed compared with CE Monte Carlo calculations, and several areas for improvement have been identified in the SCALE-XSProc MG cross section processing: (1) resonance self-shielding calculations within the unresolved resonance range, (2) 10 eV thermal cut-off energy for the free gas model, (3) on-the-fly adjustments to the thermal scattering matrix, (4) normalization of the pointwise neutron flux, and (5) fine MG energy structure. This procedure ensures very accurate MG cross section processing for high-fidelity deterministic reactor physics analysis for various advanced reactor systems.

Empirical correction of kinetic model for polymer thermal reaction process based on first order reaction kinetics

• A thermal reaction kinetic model in integral form is derived. • Correction methods are provided to compensate the variation of reaction rate. • The value of pre-exponential factor not need to be determined. • The model shows good fitting and has a very wide adaptability. Based on the theory of first-order reaction kinetics, a thermal reaction kinetic model in integral form has been derive. To make the model more applicable, the effects of time and the conversion degree on the reaction rate parameters were considered. Two types of undetermined functions were used to compensate for the intrinsic variation of the reaction rate, and two types of correction methods are provided. The model was explained and verified using published experimental data of different polymer thermal reaction systems, and its effectiveness and wide adaptability were confirmed. For the given kinetic model, only one parameter needs to be determined. The proposed empirical model is expected to be used in the numerical simulation of polymer thermal reaction process.

Recent advances in homogeneous photocatalytic carboxylation incorporated with CO<sub>2</sub>

<p indent="0mm">Carbon dioxide (CO₂) has the advantages of low price, non-toxic, abundant and renewable. As CO₂ is an indispensable part of natural photosynthesis, it seems feasible to achieve artificial CO₂ fixation with the aid of light. For light-driven utilization of CO₂, two major categories can be diversified: (1) Photoreduction of CO₂ into other C1 resources, such as carbon monoxide, methanol, formic acid, and methane; (2) photocarboxylation, which is a green and sustainable method of fixing CO₂ into organic molecules. Therefore, taking CO₂ as a C1 synthon to participate in the reaction is an effective means to utilize it. Carrying out carboxylation reaction with CO₂ as raw material to produce acrylic acid, benzoic acid or other high value-added carboxylic acid derivatives has been a very important research significance. The carboxylation reactions using CO₂ usually include: (1) The use of strong nucleophiles such as Grignard reagents; (2) the use of stoichiometric metal reducing agents; (3) high temperature, high pressure and other conditions to activate the thermodynamic and dynamic stable CO₂. In the past decade, the homogeneous photocatalytic reaction has made a great progress. Researchers found photocatalytic organic reactions have many advantages, such as mild reaction conditions, high selectivity, and environmental protection. Compared to conventional thermal reaction system with CO₂ in the carboxylation reaction, the carboxylation reaction in photocatalysis has the following advantages: (1) Avoid the utilization of unstable strong reductant; (2) most of the reaction under mild conditions are performed; (3) during the reaction and post-processing to reduce the environmental impact. This article mainly introduces and summarizes the homogeneous carboxylation reactions involving photocatalytic CO₂ in recent years. At the same time, the study of mechanism is also an important part in the homogeneous photocatalytic reaction, especially in the field of the carboxylation reactions. The current photocatalytic carboxylation reaction can be roughly divided into three categories: (1) The electron transfer process occurs between the substrate and the photocatalyst, and the nucleophilic attack on the CO₂ molecule occurs after the formation of the corresponding anion intermediate to achieve carboxylation; (2) single electron transfer (SET) occurs between the CO₂ molecule and the photocatalyst, forming a CO₂ radical anion and then reaction with the substrates; (3) with assistant of the transition metal to form complex with the substrate and/or CO₂, a series of photocatalytic electron transfer processes and ligand transfer reactions to achieve the carboxylation. In addition, there is a carboxylation reaction realized by a synergistic [4+2] mechanism. Considering the importance of the study on the reaction mechanism in organic catalytic reactions, this article will focus on the employ the different types of intermediates generated in the reaction to achieve the homogeneous photocatalytic carboxylation of various substrates with CO₂, which include four types reaction mechanisms such as anionic intermediates, CO₂ radical anions, transition metal participation, and synergistic processes.

Photocatalytic uphill conversion of natural gas beyond the limitation of thermal reaction systems

Dry reforming of methane is one of the key reactions to exploit natural gas feedstocks by their catalytic conversion to synthesis gas (CH4 + CO2 → 2H2 + 2CO), which is used in the production of transportable liquid fuel. However, this reaction suffers from thermodynamic conversion limits and high thermal energy requirements. Herein we report that a SrTiO3-supported rhodium (Rh/STO) catalyst efficiently promotes methane reforming under ultraviolet light irradiation without heat supply at low temperatures, which cannot be achieved by conventional thermal catalysis. The photoexcited holes and electrons are used for CH4 oxidation over STO and CO2 reduction over rhodium, respectively. Isotope analysis clarified that the lattice oxygens (O2−) act as mediator to drive dry reforming of methane. The materials design of Rh/STO can be extended in principle to diverse uphill reactions that utilize photon energy to obtain valued products from different carbon resources. Despite its potential, catalytic dry reforming of methane has not yet reached practical application due to high thermal energy requirements. Now, a photocatalytic method is introduced based on strontium titanate-supported rhodium nanoparticles that afford syngas production solely under light irradiation.

Extraction of alumina from high-alumina coal ash using an alkaline hydrothermal method

As a type of industrial solid waste with huge emission and heap stock, high-aluminum pulverized coal ash has a significant negative impact on resources and the environment. At the same time, as a secondary resource, its aluminum content can reach 50%, which is close to that of medium-grade bauxite; thus, it can be used as a substitute for bauxite resources. We propose a new method for extracting aluminum from fly ash via leaching. By designing the thermal reaction system of the molten brine, high-purity hydroxyl sodalite (90.2%) was prepared from fly ash. In this study, aluminum and other valuable elements were extracted using a hydrochloric acid leaching method from prepared high-purity hydroxyl sodalite in the form of ions by converting fly ash into a fixed hydroxyl sodalite solid product system. The major factors affecting the leaching rate are the hydrochloric acid concentration, liquid–solid product quality ratio, reaction temperature, and reaction time. Through analysis and calculation, within the scope of study, the leaching rate of aluminum reached more than 90%. The optimal experimental conditions are a leaching concentration of 1.5 mol/L, a liquid–solid volume–mass ratio of 20, a leaching time of 120 min, and a leaching temperature of 85 °C. Aluminum exists in the leaching solution in the form of Al3+, while the silica is partly dissolved in the hydrochloric acid solution; the other part remains in the solid phase as the main part of the hydrochloric acid leaching residue in the form of silica gel. In addition, this method not only can treat high-alumina fly ash, but also can be applied to other types of fly ash.

An overview on neutronic simulation schemes for reactor transient and safety analysis

The prediction of dynamic behavior of neutron distribution is essential for both design and safety analysis. In the present article, we have attempted to summarize various models for the analysis of time-dependent behavior of the thermal reactor systems currently under design. The underlying equations and various computer codes developed have also been presented. An overview has been presented on the current status of the reactor kinetics capabilities for thermal reactor design and analysis. As the new reactor concepts are being proposed, it has become essential to extend the design and safety analysis to multi-physics modeling. The recent work on the development of coupled neutronic–thermal–hydraulic capabilities for modern reactor designs such as AHWR, HTRs, and MSRs has also been presented.

Pyrolytic characteristics and kinetic studies of agricultural wastes—Four kinds of grasses

ABSTRACTSeveral grasses are among the agricultural wastes generated annually in a large quantity during farming activities. In this study, thermogravimetric analysis was used to evaluate the fuel properties of a number of grasses, including Aeluropus sinensis, Conyza canadensis, Imperata cylindrica, and Setaria viridis. The pyrolysis behavior was also compared with the other biomasses. The thermal reaction systems fitted well with the distributed activation energy model and the global kinetic model and it is obvious that the values of E and k0 calculated by the distributed activation energy model were much higher than that of the global kinetic model.

Formulation of a point reactor kinetics model based on the neutron telegraph equation

A Telegraph model of the Point Reactor Kinetics (TPRK) is developed based on the monoenergetic, non-fractional order telegraph approximation of the neutron transport equation. The model was used to develop a complete theory of the point reactor kinetics based on the non-fractional neutron telegraph equation. The inhour equation in the new form was obtained alongside different known reactor kinetics approximations applied to the model and their analytical solutions. The matrix form of the model was also obtained, which is needed for numerical solutions of the model. We solved this model for a step insertion of reactivity for an infinite thermal nuclear reactor system. In our model the value of the velocity of the neutrons propagation is finite and equals v/3 because of the neutron telegraph equation. Although this value is still under research, it is different from infinite as in the diffusion approximation which contradicts causality. Values of the relaxation time (τ), which is the main difference between the (TPRK) and the Diffusion Point Reactor Kinetics (DPRK), is studied for different materials based on theoretical approach and its effect on the neutron density calculations have been calculated. The most important notice in the solution of the (TPRK) model is that there is a relaxation (retardation) in the time response of the solution. This is similar to what was found earlier in the literature concerning the solutions of the neutron telegraph equation.

Investigation of waste incineration of fluorotelomer-based polymers as a potential source of PFOA in the environment

In light of the widespread presence of perfluorooctanoic acid (PFOA) in the environment, a comprehensive laboratory-scale study has developed data requested by the U.S. Environmental Protection Agency (EPA) to determine whether municipal and/or medical waste incineration of commercial fluorotelomer-based polymers (FTBPs) at end of life is a potential source of PFOA that may contribute to environmental and human exposures. The study was divided into two phases (I and II) and conducted in accordance with EPA Good Laboratory Practices (GLPs) as described in the quality assurance project plan (QAPP) for each phase. Phase I testing determined that the PFOA transport efficiency across the thermal reactor system to be used in Phase II was greater than 90%. Operating at 1000°C over 2s residence time with 3.2–6.6mgdscm−1 hydrogen fluoride (HF), corrected to 7% oxygen (O2), and continuously monitored exhaust oxygen of 13%, Phase II testing of the FTBP composites in this thermal reactor system yielded results demonstrating that waste incineration of fluorotelomer-based polymers does not result in the formation of detectable levels of PFOA under conditions representative of typical municipal waste combustor (MWC) and medical waste incinerator (MWI) operations in the U.S. Therefore, waste incineration of these polymers is not expected to be a source of PFOA in the environment.

Energy from thorium—An Indian perspective

Nuclear energy as a sustainable resource in India has been very clearly formulated in the three stage nuclear programme. The role of thorium as a potential fuel in the third stage of this programme has also been elucidated. With this aim there have been pioneering research efforts in all aspects of the thorium fuel cycle. Thorium being fertile and not accompanied by the fissile species requires the use of a fissile topping. There have been several studies in India on the use of thorium in different reactor systems from thermal to intermediate and fast spectrum, molten salt reactors, high temperature reactors, compact nuclear power packs and even Subcritical systems. In this paper, we present some of the research studies on use of thorium in thermal reactor systems. We give an overview of the neutronic properties of thorium and the bred fissile material and then proceed to show the performance potential in different reactor systems. We also present the innovative Indian reactor designs which utilize thorium, namely the Advanced Heavy Water Reactor (AHWR) and the Indian High Temperature Reactors.

Power spectral analysis for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source

A series of power spectral analyses for a thermal subcritical reactor system driven by a pulsed 14 MeV neutron source was carried out at Kyoto University Critical Assembly (KUCA), to determine the prompt-neutron decay constant of the accelerator-driven system (ADS). The cross-power spectral density between time-sequence signal data of two neutron detectors was composed of a familiar continuous reactor noise component and many delta-function-like peaks at the integral multiple of pulse repetition frequency. The prompt-neutron decay constant inferred from the reactor noise component of the cross-power spectral density was consistent with that obtained by a pulsed neutron experiment. However, the reactor noise component of the auto-power spectral density of each detector was hidden by a white chamber noise in the higher-frequency range and this feature resulted in a considerable underestimation of the decay constant. For several runs with a low pulse-repetition frequency, furthermore, we attempted to infer the decay constant from point data of the delta-function-like peaks. The analysis for a run under a slightly subcritical state resulted in the consistent decay constant; however, those for other runs under significantly subcritical states underestimated the decay constant. Considering the contribution of a spatially higher mode to the point data, the above underestimation was solved to obtain the consistent decay constant. While the Feynman-α formula for a pulsed neutron source is too complicated to be fitted directly to variance-to-mean ratio data, the present analysis on frequency domain is much simpler and the conventional formula based on the first-order reactor transfer function is available for fitting to power spectral density data.

Structure and Properties of Microwave Absorption Ag/Fe3O4 Nanoparticles

The authors report the microwave absorption Ag/Fe3O4 nanoparticles fabricated through an ethylene glycol thermal reaction systems in one pot and a silver mirror reaction coating silver to the surface of Fe3O4 nanoparticles, respectively. The result shows monodispersity spheroidic Ag/Fe3O4 nanoparticles have been successfully fabricated, and they exhibit ferromagnetic behavior with high saturation magnetization. Microwave absorption performance shows the coating of Ag to the surface of Fe3O4 nanoparticles has indeed increased the ability of electromagnetic shielding at 2–18 GHz, and the reflection ability of Ag-Fe3O4 nanocomposites at 13–16 GHz is much superior to both Fe3O4 and Ag@Fe3O4 nanoparticles.

Application of the Modified Source Multiplication (MSM) Technique to Subcritical Reactivity Worth Measurements in Thermal and Fast Reactor Systems

The Amplified Source Multiplication (ASM) method and its improved Modified Source Multiplication (MSM) method have been widely used in the CEA's EOLE and MASURCA critical facilities over the past decades for the determination of reactivity worths by using fission chambers in subcritical configurations. They have been successfully applied to absorber (single or clusters) worth measurement in both thermal and fast spectra, or for (sodium or water) void reactivity worths. The ASM methodology, which is the basic technique to estimate a reactivity worth, uses relatively simple relationships between count rates of efficient miniature fission chambers located in slightly subcritical reference and perturbed configurations. If this method works quite well for small reactivity variation (a few effective delayed neutron fraction), its raw results needs to be corrected to take into account the flux perturbation in the fission chamber. This is performed by applying to the measurement a correction factor called MSM. Its characteristics is to take into account the local space and energy variation of the spectrum in the fission chamber, through standard perturbation theory applied to neutron transport calculation in the perturbed configuration. The proposed paper describes in details both methodologies, with their associated uncertainties. Applications on absorber cluster worth in the MISTRAL-4 full MOX mock-up core and the last core loaded in MASURCA show the importance of the MSM correction on raw data.

Evaluation and use of the prompt fission neutron spectrum and spectra covariance matrices in criticality and shielding

The prompt fission neutron spectra covariance matrices of 235U, 238U and 239Pu were evaluated using the Monte Carlo method for two empirical spectra formulations, Watt and Kornilov, and compared to the existing evaluations such as JENDL-3.3. The fission spectra, together with the covariance matrices and the methods for the calculation of the corresponding sensitivity profiles were validated on several applications, including shielding (VENUS-3 benchmark, pressure vessel dosimetry) as well as on fast and thermal reactor systems (KRITZ and SNEAK critical experiments). A new set of parameters for a Kornilov model is proposed that improve both benchmark performance and the agreement with recently measured differential spectra. A recommendation to use constrained sensitivity coefficients was confirmed for the case of the fission spectrum induced uncertainty in the effective multiplication factor ( k eff ) and in the detector responses, in order to assure the proper normalisation of the corresponding covariance matrices.

Plutonium management with thorium-based fuels and inert matrix fuels in thermal reactor systems

The plutonium that is produced by light water reactors worldwide is currently re-used to a limited extent. In the last century, the expected introduction of fast reactors and the associated need for large amounts of plutonium did not take place. The result is that worldwide a stockpile of excess plutonium has formed, which is the dominant contributor to the radiotoxicity of spent nuclear fuel for storage times from ∼10 2 to 10 5 years. One option to reduce or stabilize the plutonium stockpile is to utilize this plutonium in advanced fuel types, such as thorium-based and inert matrix fuels. Because these fuels do not contain uranium, the plutonium consumption rate is very high. In this paper, the status of the fuel research and some recent developments are given.

High-Temperature Heat Exchanger Tube-Sheet Assembly Investigation With Computational Fluid Dynamics

Many modern sulfur recovery unit process waste heat recovery exchangers operate in high-temperature environments. These exchangers are associated with the thermal reactor system where the tube-sheet–tube-ferrule assemblies are exposed to gasses at temperatures approaching 3000°F. Because sulfur compounds are present in the process gas, the carbon steel tube sheet and tubes in the assembly will be deteriorated by sulfidation as the operating metal temperature rises above 600°F. Ferrule systems are used to protect the carbon steel from exposure to excessive temperatures. The temperature distribution in the steel tube-sheet–tube-ferrule system is affected by process gas flow and heat transfer through the assembly. Rather than depend on “assumed” heat transfer coefficients and fluid flow distribution, a computational fluid dynamics investigation was conducted to study the flow fields and heat transfer in the tube-sheet assembly. It was found that the configuration of the ferrule installation has a large influence on the temperature distribution in the steel materials and, therefore, the possible sulfidation of the carbon steel parts.