Pulsed Reactor Research Articles

Studying the dependence of the ratio of the prompt neutron yields in the symmetric and asymmetric fission of 235U and 238U nuclei on the energy of neutrons inducing this fission

The ratios have been measured of the prompt neutron yields in the symmetric and asymmetric fission of 235U nuclei induced by thermal neutrons and fast neutrons of pulsed nuclear reactors, as well as in the 238U fission induced by 14.7-MeV neutrons. The well-known measured integrated cross sections of the system of dosimetric nuclear reactions are compared to the cross sections calculated using the differential cross sections from the data libraries known worldwide, the three-component representation of fission neutron spectra from 235U and 252Cf nuclei, and the KASKAD spectrum reconstruction program.

EPR/PTFE Dosimetry for Test Reactor Environments

Abstract In 1992 the Radiation Metrology Laboratory (RML) at Sandia National Laboratories implemented EPR/Alanine capabilities for use in routine and calibration activities at its Co-60 and pulsed-power facilities. At that time it also investigated the usefulness of the system for measurement of absorbed dose in the mixed neutron/photon environments of reactors such as the Sandia Pulsed Reactor and the Annular Core Research Reactor used for hardness testing of electronics. The RML concluded that the neutron response of alanine was a sufficiently high fraction of the overall dosimeter response that the resulting uncertainties in the photon dose would be unacceptably large for silicon-device testing. However, it also suggested that non-hydrogenous materials such as polytetrafluoroethylene (PTFE) would exhibit smaller neutron response and might be useful in mixed environments. Preliminary research with PTFE in photon environments indicated considerable promise, but further development was not pursued at that time. Because of renewed interest in absorbed dose measurements that could better define the individual contributions of photon and neutron components to the overall dose delivered to a test object, the RML has re-initiated the development of an EPR/PTFE dosimetry system. This paper presents a summary of the research, a description of the EPR/PTFE dosimetry system, and recommendations for preparation and fielding of the dosimetry in photon and mixed neutron/photon environments.

Experimental investigation of hydrogen production through heavy naphtha cracking in pulsed DBD reactor

Abstract Cracking of heavy naphtha is studied experimentally in a nanosecond pulsed DBD plasma reactor. The system has been evaluated for instant production of light gaseous hydrocarbons in the range of C1–C3 and hydrogen via continuous hydrocarbons cracking at room temperature and atmospheric pressure. The effect of some process parameters such as reactor geometry/gap distance, carrier gas and feed flow rates have been considered on the reactor performance, experimentally. Results indicate that the less carrier gas and feed flow rates cause more energy efficiency. The maximum process efficiency is found for carrier gas and feed flow rates of 50 and 1 ml/min, respectively, which gets higher to 106.23 l/kWh for 11.50 W input power and 1.35 mm inner electrode diameter. Furthermore, results proof that for cracking process in DBD reactors there is an optimum diameter to maximize the process efficiency. For the reactor studied here, the optimum diameter of inner electrode is 2.68 mm. In this case energy efficiency of the process is 159.29 l/kWh. Results indicates that the hydrocarbon product distribution during the process is C2 > C1 ≫ C3 > C4.

Ion energy distribution measurements in rf and pulsed dc plasma discharges

A commercial retarding field analyzer is used to measure the time-averaged ion energy distributions of impacting ions at the powered electrode in a 13.56 MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The study is carried out in argon discharges at 10 mTorr where the sheaths are assumed to be collisionless. The analyzer is mounted flush with the powered electrode surface where the impacting ion and electron energy distributions are measured for a range of discharge powers. A circuit model of the discharge, in combination with analytical solutions for the ion energy distribution in radio-frequency sheaths, is used to calculate other important plasma parameters from the measured energy distributions. Radio-frequency compensated Langmuir probe measurements provide a comparison with the retarding field analyzer data. The time-resolved capability of the retarding field analyzer is also demonstrated in a separate pulsed dc magnetron reactor. The analyzer is mounted on the floating substrate holder and ion energy distributions of the impinging ions on a growing film, with 100 ns time resolution, are measured through a pulse period of applied magnetron power, which are crucial for the control of the microstructure and properties of the deposited films.

Past and present of time-of-flight small-angle neutron scattering at IBR-2

A historical overview of MURN-YuMO instrument (including some technical and scientific development prospects) is presented. Numerous references are cited which demonstrate a tireless activity on the first in the world SANS machine functioning at a neutron pulsed reactor. The relevant scientific activity trajectories of Yu.M.Ostanevich and his colleagues are retraced and put into perspective.

Study of Geometry Structure on a Wire–Plate Pulsed Corona Discharge Reactor

The wire-plate pulsed corona discharge reactor has been regarded as the plasma reactor with highest efficiency for controlling pollutants such as NO and SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> in flue gas with high-voltage and short-duration positive pulsed corona discharge. A laboratory-scale pulsed corona discharge reactor with wire-plate electrode configuration is established for optimizing the geometry structure of the wire-plate plasma reactor. In this paper, three different methods are used to optimize the wire-to-wire distance and wire-to-plate distance of the plasma reactor. There are experiments with different conditions including various electrical parameters, streamer parameters, and NO oxidation efficiency. The same results are obtained from all the three experiments. The results indicate that short wire-to-plate distance should be adopted to increase the input energy of the plasma reactor but not too short to cause spark discharge in the reactor. Moreover, the wire-to-wire distance should be at least twice as large as wire-to-plate distance, to reduce the interferences between adjacent wire electrodes.

New Measurements and the Associated Unfolding Methodologies to Characterize the Caliban Pulsed Reactor Cavity Neutron Spectrum by the Foil Activation Method

Abstract Caliban is a cylindrical metallic core reactor mainly composed of uranium 235. It is operated by the Criticality and Neutron Science Research Laboratory located at the French Atomic Energy Commission research center in Valduc. As with other fast burst reactors, Caliban is used extensively for determining the responses of electronic parts or other objects and materials to neutron-induced displacements. Therefore, Caliban’s irradiation characteristics, and especially its central cavity neutron spectrum, have to be very accurately evaluated. The foil activation method has been used in the past by the Criticality and Neutron Science Research Laboratory to evaluate the neutron spectrum of the different facilities it operated, and in particular to characterize the Caliban cavity spectrum. In order to strengthen and to improve our knowledge of the Caliban cavity neutron spectrum and to reduce the uncertainties associated with the available evaluations, new measurements have been performed on the reactor and interpreted by the foil activation method. A sensor set has been selected to sample adequately the studied spectrum. Experimental measured reaction rates have been compared to the results from UMG spectrum unfolding software and to values obtained with the activation code Fispact. Experimental and simulation results are overall in good agreement, although gaps exist for some sensors. UMG software has also been used to rebuild the Caliban cavity neutron spectrum from activation measurements. For this purpose, a default spectrum is needed, and one has been calculated with the Monte-Carlo transport code Tripoli 4 using the benchmarked Caliban description.

Naphtha cracking through a pulsed DBD plasma reactor: Effect of applied voltage, pulse repetition frequency and electrode material

In this study, a nano second pulsed dielectric barrier discharge plasma reactor has been investigated for conversion of heavy naphtha. Continuous liquid hydrocarbons cracking and instant production of hydrogen and light gaseous hydrocarbons in the range of C1–C3 have been studied at room temperature and atmospheric pressure by using argon as a carrier gas. The effect of applied voltage, pulse frequency and inner electrode material has been examined on the quantity and quality of products. Aluminum, copper, stainless steel, iron and brass have been selected to investigate the effect of electrode material. Results show that applied voltage, pulse repetition frequency and inner electrode material, affect the energy efficiency of the plasma cracking process. Stainless steel has been selected due to its high performance among all tested materials. The highest process efficiency has been obtained at 7kV and 18kHz which was 79.38lkWh−1 for 1mlmin−1 of feed injection and 24.70W input power. In this condition, the generation rate of hydrocarbon is 22.50mlmin−1. Results indicate that the hydrocarbon product distribution during the process is ethylene≫C2>C1≫C3.

Catalytic dehydrogenation of cyclohexane over Ag-M/ACC catalysts for hydrogen supply

Dehydrogenation of cyclohexane to benzene has been carried out over Ag supported on activated carbon cloth (Ag/ACC) catalysts using a spray- pulse reactor. Hydrogen evolution was studied for hydrogen storage and supply system applications. The maximum rate of hydrogen evolution rate using monometallic Ag/ACC catalysts was 6.9 mmol/gmet/min for Ag loading of 10 wt%. An enhanced hydrogen evolution was observed by adding a small amount of noble metal (1 wt% Pt, Pd, Rh) to the Ag based catalysts. A synergistic effect was observed in the case of the Pt promoted catalysts on the hydrogen production were twice as compared to 10 wt% Ag catalyst only.

Study of a novel high voltage pulsed discharge reactor with porous titanium electrodes

A study was conducted regarding the degradation of methyl orange (MO) in solution using a novel pulsed discharge reactor. The effects of the electrode gap, oxygen flow rate, electrode connection method, input voltage and pulse frequency and initial solution concentration on MO removal performance (characterized by MO removal efficiency or TOC mineralization rate) were investigated. The experimental results indicated that GH of 3mm and LH of 5mm were beneficial to MO removal efficiency; a moderate oxygen flow rate of 0.16 or 0.12m3/h was favorable for MO removal efficiency or TOC mineralization rate, respectively; the positive–negative (+−) connection, i.e. the bottom titanium electrode was connected to the HV power supply and the top electrode was connected to the ground, was better than the negative–positive (−+) connection; discharge voltage of 30kV and pulse frequency of 100Hz was the reasonable choice, regarding the MO removal efficiency and TOC mineralization rate as well as the energy yield and the stable discharge status. MO in a lower initial concentration of solution was more easily to be degraded. Ozone generated during pulse discharge was likely to be one of the main active species for MO degradation, meanwhile, intermediates recalcitrant to ozone, including small molecular acids and inorganic ions, were proved to be generated. Although a higher initial MO solution concentration negatively affected the MO removal performance, it could positively influence the energy yield. A layer of titanium dioxide film was presumed to form on the surface of a titanium plate electrode.

A device for sample rotation under external load for the simultaneous measurement of strain and orientation dependent material properties by means of TOF neutron diffraction

The time-of-flight diffractometer Epsilon-MDS at the modernised pulsed reactor IBR-2M at Dubna is designed for the detection of residual and applied strains in polycrystalline materials. The instrument allows the recording of diffraction patterns with high resolution (Δd/d = 5×l0−3 to the best) over a wide wavelength band (λmax = 7.8 Å; d max = 5.6 Å). Complicated polyphase materials like rocks consisting of minerals with large unit cells and low crystal symmetry can be investigated. The diffractometer is equipped with 81 detectors positioned behind nine radial collimators at a unique Bragg angle of 2θ = 90° for the central detector and at different radial angles allowing the simultaneous measurement of nine sample directions. A pressure device for the in situ investigation of intra-crystalline strain under uniaxial load up to 150 MPa on cylindrical samples is available. The macroscopic strain on the sample surface can be determined simultaneously by means of a laser extensometer. The sample can be rotated around its axis, i.e. limited information on texture can be obtained. The simultaneous strain and CPO measurements are helpful for a better understanding of the deformational behaviour of polycrystalline materials, e.g. to investigate elastic processes in rocks before, during and after rock failure.

Treatment of Dye Wastewater by Using a Hybrid Gas/Liquid Pulsed Discharge Plasma Reactor

A hybrid gas/liquid pulsed discharge plasma reactor using a porous ceramic tube is proposed for dye wastewater treatment. High voltage pulsed discharge plasma was generated in the gas phase and simultaneously the plasma channel was permeated through the tiny holes of the ceramic tube into the water phase accompanied by gas bubbles. The porous ceramic tube not only separated the gas phase and liquid phase but also offered an effective plasma spreading channel. The effects of the peak pulse voltage, additive gas varieties, gas bubbling rate, solution conductivity and TiO2 addition were investigated. The results showed that this reactor was effective for dye wastewater treatment. The decoloration efficiency of Acid Orange II was enhanced with an increase in the power supplied. Under the studied conditions, 97% of Acid Orange II in aqueous solution was effectively decolored with additive oxygen gas, which was 51% higher than that with argon gas, and the increasing O2 bubbling rate also benefited the decoloration of dye wastewater. Water conductivity had a small effect on the level of decoloration. Catalysis of TiO2 could be induced by the pulsed discharge plasma and addition of TiO2 aided the decoloration of Acid Orange II.

Oxidative degradation of toluene and limonene in air by pulsed corona technology

The oxidative degradation of two volatile organic compounds, i.e. toluene (fossil fuel based VOC) and limonene (biogenic VOC), has been studied. A hybrid pulsed power corona reactor with adjustable energy density has been utilized for degradation of ppm level target compounds in large air flows. The observed oxidation product range features an energy density-dependent spectrum of oxygen-functional hydrocarbons, which has been qualitatively discussed on the basis of literature studies. Typically, observed stable oxidation products for both target compounds are the biocompatible carboxylic acids acetic and formic acid. Measured degradation G-values are 23 nmol J−1 at 74% conversion of 70 ppm toluene and 181 nmol J−1 at 81% conversion of 10 ppm limonene.

Study of startup conditions of a pulsed annular reactor

A new concept of reactor, which combines features of pulsed and stationary reactors, was proposed to produce intense neutronic fluxes. Such a reactor, known as Very Intense Continuous High Flux Pulsed Reactor (VICHFPR), consists of a subcritical core with an annular geometry and pulsed by a rotating reflector that acts as a reactivity modulator as it produces a short pulse (approximately equal to 1ms) of high intensity, leading the region near the pulser to prompt supercritical state.This work tends to analyze the startup conditions of a pulsed annular reactor. The neutron pulse evolution is analyzed since the reactivity modulator is brought upwards according to a helicoidal path from its initial position (distant from the core – where the multiplication factor has a subcritical value) up to the final position (near the core), in which a prompt supercritical state is reached. Part of the analysis is based on the variation of neutron reflection, which is a uniform function of the exit and reflection angles between the core and the modulator.As the initial and final parameters are known, a programming code is worked out to provide the multiplication factor and the flux intensity evolution. According to the obtained results, the conditions under which the modulator must be lifted up during the startup are established. Basically, these conditions are related to the analysis of the raising and the rotating velocities, the reflector saving and the initial distance between the reactor and the modulator.The pulsed annular reactor startup was divided into three stages. Because of its negative reactivity in the first two stages, the neutron multiplication is not large, while the last one, having a positive reactivity, shows an intense multiplication as is usually expected when handling pulsed systems. This last stage is quite sensitive to some reactor parameters such as the modulator rotation velocity and the final reactivity, but has little sensibility to the other reactor parameters.

Gas mass spectrum analysis of I-127 transmutation targets irradiated by Xi'an pulse reactor

Xe-128 in I-127 transmutation targets irradiated by Xi'an pulse reactor was analyzed by using Quadrupole Mass Spectrometer (QMS) to calculate transmutation rate and release rate. Transmutation is an alternative method to transform long-lived toxic radio nuclides to short-lived radio nuclides or stable nuclides. 127I targets were irradiated in Xi'an Pulse Reactor for the first time to simulate the transmutation behavior of 129I. After irradiation, 128Xe in the target was determinate with online isotope dilution method by Quadrupole Mass Spectrometer (QMS), so that the transmutation rate and release rate could be calculated. Release behaviors of 128Xe were investigated through melting and step-heated modes. The stepwise heating experiment was done by puncturing method. The result shows the release rate in melting mode is 99.9% (RSD = 1%) and increases with the temperature in stepwise heating mode. The technique proposed in this work is suitable for accurate determination of transmutation rate of 129I.

Catalytic decomposition of nitrogen-containing heterocyclic compounds with highly dispersed iron nanoparticles on carbons

Decomposition of pyrrole or pyridine with iron catalysts supported on carbons has been studied with a cylindrical quartz-made pulse reactor, into which liquid pyrrole or pyridine is injected as a pulse, in order to develop a novel hot gas cleanup method of removing the nitrogen present in tar as N2. The catalyst is mainly prepared by heating FeOOH precipitated onto powdery cellulose from FeCl3 solution. Nanoscale iron catalysts with the average particle sizes of 25–30nm can promote decomposition reactions of the N-containing heterocyclic compounds in inert gas at >500°C and provide N2 yields of 40–45% after the almost complete decomposition of pyrrole at 600°C or pyridine at 650–700°C. Iron catalyst with the mean size of 100–500nm, prepared from Fe(NO3)3 impregnated with a commercial activated carbon, is also active for the decomposition of the heterocyclic N-compounds, but it is almost inactive for N2 formation, the yields being as low as less than 2% in all cases. The increase in the number of pulses lowers the catalytic activity of iron nanoparticles for N2 formation, whereas in situ H2 treatment at 500°C after reaction can restore it to the almost original state. On the basis of the above-mentioned results, it is likely that the activity of iron catalyst for N2 formation from pyrrole or pyridine is very sensitive to the iron particle size, and the in situ H2 treatment is effective for recovery of the decreased catalytic performance.

Determination of the residual stress tensor in textured zirconium alloy by neutron diffraction

Results of neutron diffraction studies of crystallographic texture and residual stress tensor components in cold-worked and annealed cylindrical components made from E-110 zirconium alloy are presented. Those components are used as plugs in the fuel elements of the VVER-type reactors; the resident residual stresses influence the durability and safety of the fuel elements. The experiments were carried out on the neutron diffractometers at Dubna (the IBR-2 pulsed reactor) and Berlin Helmholtz–Zentrum (the BER II research reactor). It is shown that the samples have fiber texture that is changed considerably with annealing. The type I residual stress tensors for both samples were calculated by the BulkPathGEO model. The cold worked component has 136–166 MPa tensile residual stress in the radial direction and zero stress along the axial direction. Residual stress values in the annealed component are close to zero.

Production of heavy and superheavy neutron-rich nuclei in neutron capture processes

The neutron capture process is considered as an alternative method for production of superheavy (SH) nuclei. Strong neutron fluxes might be provided by nuclear reactors and nuclear explosions in the laboratory frame and by supernova explosions in nature. All these cases are discussed in the paper. There are two gaps of short-lived nuclei (one is the well-known fermium gap and the other one is located in the region of $Z=106$--108 and $N\ensuremath{\sim}170)$ which impede the formation of SH nuclei by rather weak neutron fluxes realized at available nuclear reactors. We find that in the course of multiple (rather ``soft'') nuclear explosions these gaps may be easily bypassed, and thus, a measurable amount of the neutron-rich long-living SH nuclei located at the island of stability may be synthesized. Existing pulsed reactors do not allow one to bypass these gaps. We formulate requirements for the pulsed reactors of the next generation that could be used for production of long-living SH nuclei. Natural formation of SH nuclei (in supernova explosions) is also discussed. The yield of SH nuclei relative to lead is estimated to be about ${10}^{\ensuremath{-}12}$, which is not beyond the experimental sensitivity for a search of SH elements in cosmic rays.

Cyclodimerization of crotonaldehyde to form cyclohexadienecarbaldehydes and tolaldehydes over solid base catalysts

The cyclodimerization of crotonaldehyde was performed over acid or base catalysts in the gas phase. We first attempted the reaction over various acid and base catalysts using a pulse reactor. The typical bases, CaO and MgO, effectively promoted the reaction to form methylcyclohexadienecarbaldehydes (MCHC) and tolaldehydes. In contrast, no significant formation of the dimers was observed over the acid catalysts, such as SiO2–Al2O3 and H-mordenite. Aluminum oxide also promoted the dimerization, indicating that the dimerization proceeds on the weaker base sites. The main products in the formed dimers were 6-methylcyclohexa-1,3-dienecarbaldehyde and o-tolualdehyde. In addition, small amounts of 4-methylcyclohexa-1,5-dienecarbaldehyde and p-tolaldehyde were produced as dimers. When the dimerization was performed over CaO, MgO, and Al2O3 using a fixed-bed flow reactor, the catalytic activities of all the catalysts significantly decreased during the initial stage of the reaction. The TG–DTA analysis of the used catalysts clearly indicated that a large amount of the condensation products had adsorbed on the catalyst surface. The maximum selectivity to the dimers (MCHC and tolaldehydes) was 38% for an approximate 30% conversion, which was obtained during the initial stage of the reaction over the Al2O3 and CaO catalysts.

The Simulation of Probability Distribution of the Burst Waiting Time of Neutron Initiation

To obtain the probability distribution of the burst waiting time of neutron initiation in a multiplying assembly, a method that simulates the neutrons that induce a persistent fission chain is introduced in this paper. By this simulation method, neutron initiation experiments performed on Godiva-II and CFBR-II at a reactivity above prompt critical and performed on Godiva-I at a reactivity above delayed critical are studied. The probability density function of the burst waiting time of these experiments is calculated, and the results agree well with those of the experiments. Based on this simulation algorithm, the strength of the delayed neutron source changing with time is also calculated, which helps in the understanding of these neutron initiation experiments conducted on the pulse reactor.