Study of microwave plasma-assisted chemical vapor deposition of poly-and single-crystalline diamond films

We study conditions for microwave plasma-assisted chemical vapor deposition of high-quality single-crystal diamond films in a CVD reactor. These conditions are studied using the results of homoepitaxial growth of polycrystalline diamond films on diamond substrates and on the basis of numerical simulation of the microwave discharge in a CVD reactor. A high-quality single-crystal diamond layer is synthesized on a synthetic, type Ib diamond substrate. The properties of the obtained monolayer are studied by means of Raman and X-ray diffraction spectroscopy as well as optical and atomic-force microscopy.     

Experimental and numerical investigation on performance of a swirling jet reactor

In this work, a three-dimensional Computational Fluid Dynamic (CFD) analysis of a swirling jet reactor was implemented to gain a better understanding of fluid dynamics into the reactor. The effect of different geometries of the reactor, by considering different diameters of the injection slots of the reactor, on flow velocity and flow pressure distributions was investigated. Firstly, a one-phase model was implemented by considering only water into the reactor. Then, a two-phase model was defined including dissolved air into the water. The inlet flow pressure was set to 0.25 bar to consider non-cavitating conditions and, then, to get more accurate results on fluid dynamics into the reactor due to the absence of cavitating conditions. Data collected from experimental tests were used to calibrate and validate the model. Results of numerical simulations were in good agreement with experimental data, showing for all the geometries a rotating flow around the central axis of the reactor and at the exit of the double cone. The highest flow velocities and flow pressure drops were observed for the reactor geometry with the smallest injection slots diameters. Finally, noise measurements were performed during another set of experimental tests by considering different inlet flow pressures.     

Behavior of cold-worked AISI-304 steel in stress-corrosion cracking process: Microstructural aspects

Austenitic stainless steel is one of the key structural materials for a wide-range of components for present nuclear power plants. Moreover, this type of steel is also foreseen as a key structural material in future reactor systems, the so-called Generation IV. However, for the successful application of these materials in new environmental conditions an integrated Research and Development program needs to be successfully completed. This work is focused to the evaluation of cold-worked AISI-304 stainless steel from 20 to 45% of cold-worked deformation by different spectroscopic techniques within the aim to study the microstructural characteristics. In particular, positron annihilation spectroscopy and small angle neutron scattering have been used for characterization of phase transformation and microstructural behavior. Furthermore, outcomes of corrosion properties of cold-worked AISI-304 stainless steel exposed for 100 and 500 h in super-critical water reactor conditions are correlated with the obtained results.     

Thermal ignition of a heterogeneous system in a stirring semibatch reactor

The thermal ignition of a heterogeneous two-phase system of two immiscible liquids in a stirring semibatch reactor was modeled. The model took into account the dispersion of one phase in the other, the mass transfer of a reagent from the disperse phase into the dispersion medium, and the bimolecular exothermal reaction that occurred in the latter. The kinetic dependences of reagent concentrations, the dynamics of reactor heating, and the critical conditions of thermal ignition were studied. It was found that the initial temperature of the reactor had a considerable effect on its dynamic behavior.     

Effect of reactor surface modification on the neutral gas temperature in a transformer-coupled toroidal plasma

Transformer-coupled toroidal plasma (TCTP) has found applications in versatile fields as a high-power-density plasma source. However, most research on TCTP has focused on plasma states in the TCTP, without any change in reactor structures. Therefore, in this paper, we present a study on the effects of inner-surface modification of a TCTP reactor on plasma conditions. Using two types of reactors with different inner surfaces, the silicon-wafer etch rate by fluorine atoms from dissociated NF₃ gas molecules is compared. Then a computer simulation, which derives various plasma parameters, is carried out. As a result, the TCTP reactor with a grooved inner surface shows a higher etch rate than the reactor with a normal inner surface. The computer simulation suggests the reason for this etch rate difference is that the reactor with the grooved inner surface structure has a higher neutral gas temperature than the reactor with the normal inner surface so that more pyrolytic dissociation, resulting in a higher fluorine atom density, is achieved. Our results may be useful for those fields that require a higher neutral temperature or a higher degree of pyrolysis.     

Electric-arc high-capacity reactor for the synthesis of carbon soot with a high content of endohedral metallofullerenes

An electric-arc reactor is designed for synthesizing carbon soot containing endohedral metallofullerenes during the sequential evaporation of five composite graphite electrodes. The preparation conditions of the composite graphite electrodes and the electric-arc evaporation parameters are optimized, which increases the reactor capacity and the content of endohedral metallofullerenes in carbon soot.     

基于FLUENT的核热耦合程序反应性反馈参数敏感性

将计算流体力学模型与中子动力学模型耦合来进行反应堆瞬态安全分析的方法,由于可以开展复杂几何结构的三维流动传热分析,因此受到很大的关注。基于FLUENT用户自定义功能（UDF）开发了一套可用于池式铅堆瞬态安全分析的核热耦合程序,程序耦合了临界/次临界点堆中子动力学模型和燃料棒模型。由于反应堆处于不同寿期时,随着燃料燃耗、可燃毒物积累等因素导致反应性反馈系数有较大变化,因此使用开发的核热耦合程序对中国科学技术大学提出的小型自然循环铅冷快堆进行不同关键反馈系数下无保护的瞬态超功率事故安全分析。调整点堆模块考虑到的四个反应性反馈系数,可以发现燃料多普勒系数对堆安全的影响最大,同时定量的分析结果表明超功率事故引入时间长短对事故演化有重要影响。     

Influence of the gamma-ray fraction in the reactor radiation on the total signal of a self-powered neutron detector

For controlling the linear power density in the reactor core, the Khortitsa-M software program as a part of the in-core instrumentation system (ICIS) employs only self-powered neutron detector (SPND) data with the neutronic calculation for the consistent determination of the power density in unmeasurable fuel assemblies (FAs). The confidence of the interpretation of the SPND data essentially determines the safe and efficient operation of a reactor. Previously, it was assumed that the gamma-ray fraction in the reactor radiation does not exceed one percent and is independent of the fuel enrichment and the FA and SPND burnups. Since it is difficult to estimate the contribution of the reactor gamma radiation to the SPND current experimentally, in this work, we present a calculated estimate using modern software and libraries of constants. On the basis of the results of this study, the question is discussed whether it is appropriate to take into account the reactor gamma radiation in the transfer function from the SPND current to the power density of six fuel elements surrounding the SPND with allowance for both the type of FA and the FA and SPND burnups.     

TPD study in LSM/YSZ/LaAlO system for the use of fuel cell type reactor

Behaviors of oxygen species in the LSM/YSZ/LaAlO SOFC type reactor were investigated. The fuel cell type temperature-programmed desorption (FC-TPD) measurements were employed in three operating modes; i.e. (1) open circuit, (2) closed circuit without applied potential and (3) closed circuit with applied potential modes. Various pretreatment conditions, i.e. (a) open circuit, (b) closed circuit without applied potential and (c) closed circuit with applied potential, were investigated. The FC-TPD technique enables to discuss the oxygen species responsible for a combustion reaction and those for a coupling reaction, separately. The open circuit type FC-TPD showed that the applied potential during the pretreatment caused the increase in the amount of surface oxygen and the decrease in activation energy of desorption of oxygen at the anode catalyst. The closed circuit FC-TPD provided the combined effects of desorption and permeation. In addition, the FC-TPD analysis could correlate the behavior of adsorbed oxygen species to the NEMCA effect observed in the oxidative coupling of methane in the SOFC reactor.     

Heat and mass transfer intensification in coaxial reactor

The work considers heat and mass transfer in the homophasic polymerization reactor. The reactor is a coaxial channel with internal tube in the form of a channel of confusor-diffuser type. The authors compared the degree of polymer transformation in the intensified coaxial reactor with internal tube of confusor-diffuser type and the reactor with constant rectilinear longitudinal section. It was found that in coaxial channels with internal tube of confusor-diffuser type, it is possible to reach high values of the transformation degree and to improve the quality of the obtained polymer.     

Sonoelectrochemical hydrogenation of safrole: A reactor design,statistical analysis and computational fluid dynamic approach

In this work, ultrasound-assisted electrocatalytic hydrogenation (US-ECHSA) of safrole was carried out in water medium, using sacrificial anode of nickel. The ultrasonic irradiation was carried out at frequency of 20 kHz ± 500 Hz with a titanium cylindrical horn (MS 73 microtip; Ti-6AI-4V alloy; 3.0 mm diameter). The optimal conditions were analyzed by statistical experimental design (fractional factorial). The influence of the sonoelectrochemical reactor design was also investigated by using computational fluid dynamics as simulation tool. Among the five parameters studied: catalyst type, use of β-cyclodextrin as inverse phase transfer catalyst, sonoelectrochemical reactor design, ultrasound mode and the temperature of the solution, only the last three were significant. The hydrogenation product, dihydrosafrole, reached 94% yield, depending on the experimental conditions applied. Data of computational fluid dynamics showed that a wing shape tube added to the sonoelectrochemical reactor can work as a cooling apparatus, during the electrochemical process. The reactional solution temperature diminishes 14 °C when compared to the four-way-type reactor. Cooper cathode, absence of β-cyclodextrin, four-way-type reactor, ultrasound continuous mode (14 W) and absence of temperature control were the most effective reaction parameters for the safrole hydrogenation using US-ECHSA method. The proposed approach represents an important contribution for understanding the hydrodynamic behavior of sonoelectrochemical reactors designs and, consequently, for the reducing of the experimental costs inherent to the sonoelectrochemical process.     

The procedure and results of calculations of the equilibrium isotopic composition of a demonstration subcritical molten salt reactor

A subcritical molten salt reactor with an external neutron source is studied computationally as a facility for incineration and transmutation of minor actinides from spent nuclear fuel of reactors of VVER-1000 type and for producing ²³³U from ²³²Th. The reactor configuration is chosen, the requirements to be imposed on the external neutron source are formulated, and the equilibrium isotopic composition of heavy nuclides and the key parameters of the fuel cycle are calculated.     

Comparison of two different ultrasound reactors for the treatment of cellulose fibers

The pulp and paper industry is in continuous need for energy-efficient production processes. In the refining process of mechanical pulp, fibrillation is one of the essential unit operations that count for up to 80% of the total energy use. This initial study explores the potential and development of new type of scalable ultrasound reactor for energy efficient mechanical pulping. The developed reactor is of continuous flow type and based on both hydrodynamic and acoustic cavitation in order to modify the mechanical properties of cellulose fibers. A comparison of the prototype tube reactor is made with a batch reactor type where the ultrasonic horn is inserted in the fluid. The pulp samples were sonicated by high-intensity ultrasound, using tuned sonotrodes enhancing the sound pressure and cavitation intensity by a controlled resonance in the contained fluid. The resonant frequency of the batch reactor is 20.8 kHz and for the tube reactor it is 22.8 kHz. The power conversion efficiency for the beaker setup is 25% and 36% in case of the tube reactor in stationary mode. The objective is to verify the benefit of resonance enhanced cavitation intensity when avoiding the effect of Bjerkenes forces. The setup used enables to keep the fibers in the pressure antinodes of the contained fluid. In case of the continuous flow reactor the effect of hydrodynamic cavitation is also induced. The intensity of the ultrasound in both reactors was found to be high enough to produce cavitation in the fluid suspension to enhance the fiber wall treatment. Results show that the mechanical properties of the fibers were changed by the sonification in all tests. The continuous flow type was approximately 50% more efficient than the beaker. The effect of keeping fibers in the antinode of the resonant mode shape of the irradiation frequency was also significant. The effect on fiber properties for the tested mass fraction was determined by a low-intensity ultrasound pulse-echo based measurement method, and by a standard pulp analyzer.     

Self-Ignition and Combustion of Gas Mixtures in a Medium with Vortex Flow

Experiments carried out in a rapid-injection setup with tangential introduction of the mixture into the reactor show that the mixtures self-ignite at temperatures substantially lower than the values reported in the literature. The measured ignition delay times do not exceed 0.1–0.2 s, although thermal conditions in the reactor allow the mixture to ignite with delays of more than 10 s. Videorecording shows that the mixture spontaneously ignites in a small volume at the center of the reactor; i.e., tangential mixture injection produces a vortex with a hotspot having a temperature at its center by more than 200 K higher than that of the reactor walls. An obstacle destroying the vortex eliminates the anomalous behavior of the self-ignition process. Temperatures measured at the center of the reactor with a thermocouple confirm the formation of a hotspot. The flame initiated by the ignition at a hotspot propagates through the mixture at a velocity several times higher than the laminar flame speed characteristic of the mixture. The mechanism of the formation of hotspots in unsteady vortex flows and their possible effect on explosion risk assessment in some practical situations are discussed.     

Optimization of the physical characteristics and the regime of uniform partial refuelings of a fast nuclear reactor

This paper covers some specific features of the optimization problem with integer-valued and continuously changing parameters that has been formulated for a fast reactor operating under the steady-state regime of the uniform partial refueling. Effective algorithms for calculating the physical characteristics and an iterative procedure of constructing optimum values of parameters are proposed. The paper considers the solution of a problem on minimization of the loss of energy generation in a reactor of the BREST-800 type that occurs because average fuel burnup in fuel assemblies being removed does not achieve its maximum permissible level. For several core arrangements, the comparison with nonoptimum solutions is given and the role of various factors contributing to an increase in average fuel burnup is evaluated.     

Investigation of ammonia stripping with a hydrodynamic cavitation reactor

Ammonia is a commonly used compound in the domestic and industrial fields. If ammonia found in wastewater after use is not treated, even at low concentrations it may cause toxic effects in the receiving environment. In this study, a hydrodynamic cavitation reactor (HDC) was designed with the aim of removing ammonia. The effect of parameters like different cavitation numbers, airflow, temperature and initial concentration on NH₃ removal was researched. The potential of hydrodynamic cavitation for removal of volatile gases, like NH₃, was assessed with the aid of two film theory mathematical equations. Experimental studies were performed at fixed pH = 11. Under the conditions of 0.12 cavitation number, 25 L/min airflow, 30 °C temperature and 2500 mg/L initial concentration, in 24 h 98.4% NH₃ removal efficiency was achieved. With the same experimental conditions without any air, the HDC reactor provided 89.5% NH₃ removal at the end of 24 h.The HDC reactor is very effective for the removal of volatile gases from wastewater and it was concluded that even in the absence of aeration, the desired NH₃ removal efficiency was provided.     

Thermal regimes of a counterflow reactor: a gas-liquid system

A counterflow reactor model for a system of two phases one of which involves an exothermic bimolecular reaction is considered. At a stationary temperature distribution in the reactor, there are high and low heating regions. For the adiabatic case, maximum heating is only possible at the bottom of the reactor. The maximum stationary temperature in the reactor decreases and shifts toward the top of the reactor as the intensity of heat exchange with the environment increases.     

Preliminary results of calculations for heavy-water nuclear-power-plant reactors employing <Superscript>235</Superscript>U, <Superscript>233</Superscript>U,and <Superscript>232</Superscript>Th as a fuel and meeting requirements of a nonproliferation of nuclear weapons

A physical design is developed for a gas-cooled heavy-water nuclear reactor intended for a project of a nuclear power plant. As a fuel, the reactor would employ thorium with a small admixture of enriched uranium that contains not more than 20% of ²³⁵U. It operates in the open-cycle mode involving ²³³U production from thorium and its subsequent burnup. The reactor meets the conditions of a nonproliferation of nuclear weapons: the content of fissionable isotopes in uranium at all stages of the process, including the final one, is below the threshold for constructing an atomic bomb, the amount of product plutonium being extremely small.     

Formation of Si-nanoparticles in a microwave reactor: Comparison between experiments and modelling

The formation and growth of silicon-nanoparticles from silane in a microwave reactor was investigated. Experiments were performed for the following conditions: precursor concentration 380–2530 ppm, pressures of 20–30 mbar, microwave powers 120–300 W. The formed particles were examined in-situ with a particle mass spectrometer. Additionally, particles were collected on grids and analyzed by transmission electron microscopy, X-ray diffraction, and by determining the specific surface area by BET. The particle size was found to be in the range of 5–8 nm in diameter. A simple model was used to simulate the particle formation processes taking place inside the reactor. The microwave energy coupled into the reactor flow was treated as a spatially distributed energy source resulting in a local temperature increase. The particles were assumed to have a monodisperse size distribution. To allow an approximation of their shape they were characterized by their volume and surface area. The model takes nucleation, convection, coagulation, and coalescence into account. The fluid flow inside the microwave reactor was simulated with the commercial CFD-code Fluent.     

堆振荡器法测量反应性的误差因素分析

为合理选择堆振荡器法实验条件,利用数值求解和公式推导,对影响测量精度的几项主要因素进行了分析。研究表明,通过选择合适的反应性振荡幅度及频率,可以提高堆振荡器法测量反应性的精度。由分析结果可知,对于中子代时间较短的反应堆,要使用堆振荡器法测量小反应性,在测量条件允许的情况下,应尽可能选择高频率的反应性振荡。