Pulsed Reactor Research Articles

Precise kinetic measurements and spatial uniformity of catalytic beds

Sufficient uniformity of the gas phase and surfaces within a catalytic bed is an essential prerequisite for precise kinetic characterization of heterogeneous catalysts. In addition to uniformity, the gas transport regime must be mathematically well-defined and allow for controlled alterations of the catalyst state. The Thin-Zone Temporal Analysis of Products (TZTR) reactor satisfies these requirements for industrially-relevant powdered catalysts. Numerical simulations of pulse-response experiments were used to chart the conditions of spatial uniformity within the TZTR for very fast (DaII up to 100) irreversible reactions, such as strong chemisorption or oxidation reactions. The simulations demonstrated that even when an initial catalyst state is so reactive that uniformity cannot be readily achieved, a series of reactant pulses eventually creates a catalyst state which is spatially uniform and at the same time reactive enough for kinetic characterization. This point on the scale of possible catalyst states is attained when the total amount of pulsed molecules exceeds the initial number of active sites in the sample, i.e. the theoretical monolayer coverage. Simulations also indicated that the rate at which the catalyst bed becomes more uniform from one pulse to the next is sensitive to reaction order: the desired uniformity is established for a second order adsorption after smaller amount of pulses than for a first order adsorption. Thus, a wider range of spatially uniform, yet kinetically-relevant catalyst states can be characterized for a second order adsorption. These results not only expand the range of validity for the TZTR approach, but also set new bounds for generally achievable precise kinetic measurements.

Low Temperature Atomic Layer Deposition of Crystalline In2O3 Films

Crystalline In2O3 thin films were deposited by atomic layer deposition (ALD) using tris(2,2,6,6-tetramethyl-3,5-heptanedionato) indium(III), [In(TMHD)3] as an indium source and O2 plasma. Resulting growth rates were studied as a function of precursor pulse, reactant pulse, deposition temperature, and number of ALD cycles. The film growth rate was found to be 0.14 A/cycle within the wide ALD temperature window of 100–400 °C. X-ray photoelectron spectroscopic (XPS) and X-ray diffraction (XRD) analysis revealed stoichiometric In2O3 thin films with polycrystalline cubic structure, even at 100 °C. All the as-deposited films were smooth, with RMS roughness values between 0.39 to 0.47 nm, as shown by atomic force microscopic (AFM) analysis. The optical properties and electrical resistivities of the films were determined by spectroscopic ellipsometry (SE) and four-point probe measurements. The highly transparent (ca. 94% in the visible region) films had a refractive index of 2.01–2.05 and a resistivity of 2.5–3 m...

On the development of the quantitative texture analysis and its application in solving problems of the Earth sciences

A history of texture analysis (TA) evolution is shown, beginning from the first experimental and theoretical attempts to find and characterize preferred orientations of crystal lattices of grains in real polycrystalline samples. Stages of formation of TA theoretical apparatus, its basic elements, and also application of its capabilities for quantitatively describing anisotropic properties of textured samples are discussed. Attention is also paid to the limitations and difficulties associated with the analysis. The application of the quantitative TA apparatus is demonstrated by example describing elastic properties of textured materials up to multiphase samples containing pores and cracks. A wide scope of TA includes the analysis based on neutron scattering which has been effectively developed at the Frank Laboratory of Neutron Physics. A practical opportunity to determine the bulk crystallographic textures of single-phase and multiphase materials is offered by the use of modern neutron diffractometers, including the SKAT diffractometer at the IBR-2 pulsed reactor. This is especially important for studying samples of natural rocks. The examples given show how the neutron scattering data for the quantitative TA are used in combination with other physical and petrological methods for solving fundamental problems of geology and geophysics based on the analysis of a structure and properties of the Earth’s lithosphere matter. The review includes a detailed list of references of original works concerning the TA elaboration, overview publications and monographs, and also information on the most popular TA-related software.

Dynamics model of the IBR-2M pulsed reactor for analysis of fast transition processes

A nonlinear model of the IBR-2M pulsed reactor dynamics relating values of variables at discreet instants of time (when power pulses appear) is developed on the basis of the MATLAB program system. The tests of the model by simulating calculated processes in the IBR-2M reactor proved the correctness of the model. A tentative estimate of the transfer coefficient for the linear part of the automatic regulator is obtained.

Correlation Fourier diffractometry: 20 Years of experience at the IBR-2 reactor

The high-resolution Fourier diffractometer (HRFD) was commissioned at the IBR-2 pulsed reactor at FLNP JINR in 1994. The specific feature of the HRFD design is the use of fast Fourier chopper for modulating the primary neutron beam intensity and the correlation method of diffraction data acquisition. This allowed to reach with HRFD extremely high resolution (Δd/d ≈ 0.001) over a wide range of inter-planar spacings at a relatively short flight path between chopper and sample (L = 20 m). Over time, a lot of diffraction experiments on crystalline materials, the main goal of which was to study their atomic and magnetic structures, were performed at HRFD. Successful implementation of the Fourier diffractometry technique at the IBR-2 reactor stimulated the construction of yet another Fourier diffractometer intended for internal mechanical stress studies in bulk materials (FSD, Fourier Stress Diffractometer). In this paper the experience of using this technique at the IBR-2, which is a long-pulse neutron source, is considered, the examples of HRFD studies are given, and possible solutions for existing technical problems of using correlation diffractometry and ways of increasing the intensity and resolution of HRFD are discussed.

Dynamic modelling of balance of plant systems for a pulsed DEMO power plant

The current baseline concept for a European DEMO defines a pulsed reactor producing power for periods of 2–4h at a time, interrupted by dwell periods of approximately half an hour, potentially leading to cyclic fatigue of the heat transfer system and power generation equipment. Thermal energy storage systems could mitigate pulsing issues; however, the requirements for such a system cannot be defined without first understanding the challenges for pulsed operation, while any system will simultaneously increase the cost and complexity of the balance of plant.This work therefore presents a dynamic model of the primary heat transfer system and associated steam plant for a water-cooled DEMO, without energy storage, capable of simulating pulsed plant operation. An operating regime is defined such that the primary coolant flows continuously throughout the dwell period while the secondary steam flow is reduced. Simulation results show minimised thermal and pressure transients in the primary circuit, and small thermally induced stresses on the steam turbine rotor. If the turbine can be kept spinning to also minimise mechanical cycling, pulsed operation of a water-cooled DEMO without thermal energy storage may be feasible.

Integral cross section measurement of theU235(n,n′)U235mreaction in a pulsed reactor

The integral measurement of the neutron inelastic cross section leading to the 26-minute half-life $^{235m}\mathrm{U}$ isomer in a fission-like neutron spectrum is presented. The experiment has been performed at a pulsed reactor, where the internal conversion decay of the isomer was measured using a dedicated electron detector after activation. The sample preparation, efficiency measurement, irradiation, radiochemistry purification, and isomer decay measurement will be presented. We determined the integral cross section for the $^{235}\mathrm{U}(n,{n}^{\ensuremath{'}})^{235m}\mathrm{U}$ reaction to be $1.00\ifmmode\pm\else\textpm\fi{}0.13\phantom{\rule{0.28em}{0ex}}\mathrm{b}$. This result supports an evaluation performed with talys-1.4 code with respect to the isomer excitation as well as the total neutron inelastic scattering cross section.

An Integrated Approach to Understanding the Mass Transfer and Reaction Processes in a Pulsed High-Voltage Discharge Reactor

The effect of pulsed high-voltage discharge on mass transfer and reaction processes in a needle-plate reactor was studied. Bubble size distributions and characteristic parameters were determined by photography, implying that inlet air bubbles could be broken into smaller ones effectively by discharge. The mass transfer parameters including specific interfacial area (a), volumetric mass transfer coefficient (kLa), and liquid-side mass transfer coefficient (kL) were obtained by Danckwerts-plot, reflecting the mass transfer processes. In addition, 4-chlorophenol (4-CP) decomposition was determined under the same experimental conditions. The results showed that the conclusions of 4-CP removal were coincided with the statistical results of bubble images, illustrating that higher peak voltage, pulsed frequency and appropriate air flow rate are beneficial to mass transfer and reaction. However, there was a slight difference between 4-CP removal and mass transfer parameters at higher air flow rate. Therefore, it is more reasonable to optimize the operating conditions of a pulsed high-voltage discharge reactor via combining image acquisition and mass transfer parameters with the results of pollutant degradation.

Irreversible and reversible reactive chromatography: Analytical solutions and moment analysis for rectangular pulse injections

This work is concerned with the analysis of models for linear reactive chromatography describing irreversible A→B and reversible A↔B reactions. In contrast to previously published results rectangular reactant pulses are injected into initially empty or pre-equilibrated columns assuming both Dirichlet and Danckwerts boundary conditions. The models consist of two partial differential equations, accounting for convection, longitudinal dispersion and first order chemical reactions. Due to the effect of involved mechanisms on solute transport, analytical and numerical solutions of the models could be helpful to understand, design and optimize chromatographic reactors. The Laplace transformation is applied to solve the model equations analytically for linear adsorption isotherms. Statistical temporal moments are derived from solutions in the Laplace domain. Analytical results are compared with numerical predictions generated using a high-resolution finite volume scheme for two sets of boundary conditions. Several case studies are carried out to analyze reactive liquid chromatographic processes for a wide range of mass transfer and reaction kinetics. Good agreements in the results validate the correctness of the analytical solutions and accuracy of the proposed numerical algorithm.

Independence of the Final Catalyst Activity Profile on the Details of Reactant Admission

It is shown analytically, based on pulse-response experiments, that under special conditions the activity profile of a prepared catalytic system depends only on the total amount of admitted substance. This property, previously found computationally, is here established mathematically for porous and nonporous catalysts in different pulse reactors.

First Attempts on Energy-selective Neutron Imaging at IBR-2

A new neutron imaging facility has been started at the IBR-2 high flux pulsed reactor. It isattractive not only for traditional neutron imaging applications but in particular also for thedevelopment of modern energy-selective techniques using a time-of-flight methods.A short overview of the first obtained results of theenergy-selected experiments by means of time-of-flight methods realised on neutron radiography and tomography station on high-flux pulsed reactor IBR-2 are presented.

DIRECT AND DELAYED DEGRADATION OF AZORUBIN (E122) BY GLIDING ARC DISCHARGES

The goal of this paper is to investigate the decomposition of aqueous solutions of Azorubin (E122), i.e., an azo dye used in food industry, in a pulsed gliding arc discharge reactor (direct treatment). Air and Argon as carrier gases with solution spray has been considered, as a first approach. The bleaching of the aqueous solution was observed immediately after direct plasma treatment and the decreasing of the dye concentration have been emphasized. Further more, the dye concentration in solution still decreases after plasma treatment in so called Temporal Post-Discharge Reactions (TPDR) conditions. Samples of the treated solution by plasma was analyzed after 1h, 2h, 4h, 8h, 24h, 98h and 120 h after the discharge was switched off, which confirms that the influence of the reactive species (e.g., OH, NO and their derivatives) formed in active plasma on dye destruction are still active after the solution treatment.

Synthesis of superheavy nuclei: Obstacles and opportunities

There are only 3 methods for the production of heavy and superheavy (SH) nuclei, namely, fusion reactions, a sequence of neutron capture and beta(-) decay and multinucleon transfer reactions. Low values of the fusion cross sections and very short half-lives of nuclei with Z>120 put obstacles in synthesis of new elements. At the same time, an important area of SH isotopes located between those produced in the cold and hot fusion reactions remains unstudied yet. This gap could be filled in fusion reactions of 48 Ca with available lighter isotopes of Pu, Am, and Cm. New neutron-enriched isotopes of SH elements may be produced with the use of a 48 Ca beam if a 250 Cm target would be prepared. In this case we get a real chance to reach the island of stability owing to a possible beta(+) decay of 291 114 and 287 112 nuclei formed in this reaction with a cross section of about 0.8 pb. A macroscopic amount of the long-living SH nuclei located at the island of stability may be produced by using the pulsed nuclear reactors of the next generation only if the neutron fluence per pulse will be increased by about three orders of magnitude. Multinucleon transfer processes look quite promising for the production and study of neutron-rich heavy nuclei located in upper part of the nuclear map not reachable by other reaction mechanisms. Reactions with actinide beams and targets are of special interest for synthesis of new neutron-enriched transfermium nuclei and not-yet-known nuclei with closed neutron shell N=126 having the largest impact on the astrophysical r-process. The estimated cross sections for the production of these nuclei allows one to plan such experiments at currently available accelerators.

Neutron Radiography Facility at IBR-2 High Flux Pulsed Reactor: First Results

A neutron radiography and tomography facilityhave been developed recently at the IBR-2 high flux pulsed reactor. The facility is operated with the CCD-camera based detector having maximal field of view of 20x20cm, and the L/D ratio can be varied in the range 200 – 2000. The first results of the radiography and tomography experiments with industrial materials and products, paleontological and geophysical objects, meteorites, are presented.

Self-consistent quasi-linear modelling of Lower Hybrid Current Drive in ITER and DEMO

First pass absorption of the Lower Hybrid waves in thermonuclear devices like ITER and DEMO is modelled by coupling the ray tracing equations for the wave phase and amplitude with the quasi-linear evolution of the electron distribution function. A system of coupled ordinary differential equations for each Fourier component of the spectrum radiated by the LH antenna is derived and solved when considering both 1D/2D Fokker-Planck model for the electron distribution function. This allows to reconstruct and to evolve the quasi-linear diffusion coefficient consistently with the wave propagation, to calculate the power deposition profile and the amount of current driven by the wave. As usually assumed, the Lower Hybrid Current Drive is not effective in a plasma of a tokamak fusion reactor like ITER or DEMO, because the high electron temperature would enhance the wave absorption and then limit the RF power deposition to the very periphery of the plasma column (near the separatrix). In this work by extensively using this self-consistent modelling for the propagation and absorption of the LH wave, a parametric study on the wave spectrum (and consequently on the antenna design) as spectrum width, peak value, secondary lobes etc. has been performed very accurately. Such a careful investigation aims at controlling the power deposition layer possibly in the external half radius of the plasma, thus providing a valuable aid to the solution of how to control the plasma current profile in a toroidal magnetic configuration. This analysis is useful not only for exploring the possibility of profile control of a pulsed operation reactor, but also in order to reconsider the feasibility of steady state regime.

When the final catalyst activity profile depends only on the total amount of admitted substance: Theoretical proof

SignificanceIt is shown, based on pulse‐response experiments, that under special conditions the activity profile of a prepared catalytic system depends only on the total amount of admitted substance. This property, previously found computationally, is here established mathematically for porous and nonporous catalysts in different pulse reactors. This result can be used as a theoretical guidance for the design of systems or materials with an optimal activity profile, in particular a catalyst bed or a catalyst particle. Consequently, it can be used for understanding and developing the different diffusion‐reaction processes, e.g., wet impregnation, deactivation of active materials, and so forth. © 2014 American Institute of Chemical Engineers AIChE J, 61: 31–34, 2015

Degradation of Acid Orange 7 Dye in Two Hybrid Plasma Discharge Reactors

To get an optimized pulsed electrical plasma discharge reactor and to increase the energy utilization efficiency in the removal of pollutants, two hybrid plasma discharge reactors were designed and optimized. The reactors were compared via the discharge characteristics, energy transfer efficiency, the yields of the active species and the energy utilization in dye wastewater degradation. The results showed that under the same AC input power, the characteristics of the discharge waveform of the point-to-plate reactor were better. Under the same AC input power, the two reactors both had almost the same peak voltage of 22 kV. The peak current of the point-to-plate reactor was 146 A, while that of the wire-to-cylinder reactor was only 48.8 A. The peak powers of the point-to-plate reactor and the wire-to-cylinder reactor were 1.38 MW and 1.01 MW, respectively. The energy per pulse of the point-to-plate reactor was 0.2221 J, which was about 29.4% higher than that of the wire-to-cylinder reactor (0.1716 J). To remove 50% Acid Orange 7 (AO7), the energy utilizations of the point-to-plate reactor and the wire-to-cylinder reactor were 1.02 × 10−9 mol/L and 0.61 × 10−9 mol/L, respectively. In the point-to-plate reactor, the concentration of hydrogen peroxide in pure water was 3.6 mmol/L after 40 min of discharge, which was higher than that of the wire-to-cylinder reactor (2.5 mmol/L). The concentration of liquid phase ozone in the point-to-plate reactor (5.7 × 10−2 mmol/L) was about 26.7% higher than that in the wire-to-cylinder reactor (4.5 × 10−2 mmol/L). The analysis results of the variance showed that the type of reactor and reaction time had significant impacts on the yields of the hydrogen peroxide and ozone. The main degradation intermediates of AO7 identified by gas chromatography and mass spectrometry (GCMS) were acetic acid, maleic anhydride, p-benzoquinone, phenol, benzoic acid, phthalic anhydride, coumarin and 2-naphthol. Proposed degradation pathways were elucidated in light of the analyzed degradation products.

Streamer Inception and Propagation in a Multiple Wire-Cylinder Pulsed Corona Reactor

Industrial application of nanosecond pulsed corona technology for air purification requires high volume, high-power plasma reactors. Cylinder-wire type reactors require multiple cylinders to meet these demands. Variations in pulse waveforms per cylinder, misalignment of wires, and jitter in streamer inception could lead to an uneven energy distribution over the cylinders. Nanosecond ICCD imaging is applied to a semiindustrial scale pulsed corona reactor to study streamer inception and propagation of the streamer plasma simultaneously in 16 cylinders. The images show streamer inception of all cylinders within 9 ns. Streamer propagation and intensities are very similar for all cylinders.

Analysis of processes in Li-ion batteries by time-of-flight neutron diffraction

Ex-situ and in-situ neutron diffraction experiments were performed at HRFD time-of-flight (TOF) diffractometer (IBR-2 long-pulsed reactor, JINR) to characterize the entire battery system based on LiFePO4 and V-added LiFePO4 electrodes during electrochemical cycling and to find additional information about crystal structure of electrodes. Another purpose of this work was checking possibilities for in-situ experiments with real Li-ion batteries at the IBR-2 pulsed reactor. An important advantage of TOF method is the possibility to work at the fixed geometry of the experiment, which allows selecting the optimal battery orientation relative to the directions of the incident and scattered neutron beams and, thus, to minimize the difficulties associated with complex internal structure of the battery. It was shown that charge/discharge process of Li-based real Li-ion battery can be effectively studied by TOF technique at the IBR-2 pulsed reactor. Three full charge/discharge cycles were realized at room temperature (~170C) with slow rate. The step-like appearance of several LiCn phases was observed and the volume fractions of LiFePO4 and FePO4 structural phases at different states of charge were determined. The analysis of changes in cathode material microstructure when doped with vanadium showed a significant increase in the density of defects, which correlates with better electrochemical properties of V-added LiFePO4 compared to pure LiFePO4.

Performance Evaluation of Hybrid Gas–Liquid Pulse Discharge Plasma-Induced Degradation of Polyvinyl Alcohol-Containing Wastewater

A multi-needle-to-plate pulsed discharge plasma reactor was designed to investigate its potential for polyvinyl alcohol-containing wastewater (PVA) treatment. The effects of some operational parameters such as PVA initial concentration, pulse peak discharge voltage, air flow rate, solution pH value, and iron additives on PVA degradation were examined. The results indicated that PVA could be effectively degraded from aqueous solutions. PVA degradation efficiency was 76.0 % within 60 min’s discharge plasma treatment with 1.5 mmol L−1 Fe2+ addition. Decreasing PVA initial concentration and increasing pulse peak discharge voltage were both beneficial for PVA degradation. There existed appropriate air flow rate for obtaining great PVA degradation efficiency in the present study. A little acid environment was conducive to PVA degradation. The presence of Fe2+ and Cu2+ could both benefit PVA degradation, and the increment of Fe2+ and Cu2+ concentrations to a certain extent could enhance its degradation efficiency, as well as energy yield. PVA possible degradation mechanisms were discussed, and the degradation processes were mainly triggered by the reactions of PVA with \(^{ \cdot } {\text{OH}}\) radicals.