最新刊期
卷 41 ， 期 6 ， 2018
- 摘要：BackgroundSpectrum smoothing can remove the statistical fluctuations in the measured energy spectrum and retain important information of the spectral peaks. Each spectrum smoothing method has its own advantages, and is not always effective in any case. PurposeThis study aims at the application of spectrum smoothing methods with different smoothing times and parameters, and evaluate smoothing methods based on smoothness and correlation coefficient respectively. MethodsA spectrum analysis tool which is integrated Gauss smoothing and Savitzky-Golay (SG) methods is designed based on Matrix Laboratory Graphical User Interface, (MATLAB GUI). It is applicable to real-time and off-line batch processing of spectral data with a few necessary steps. One spectrum captured by the graphite pre-diffraction X fluorescence analyzer is processed by the designed tool, and the correlation coefficient is introduced to evaluate the smoothness. ResultsExperimental results show that the smoothness of the Gauss smoothing is better than SG when the peak amplitude is larger. Whilst SG outperform Gauss smoothing when the peak amplitude is small. The Gauss smoothing parameters are more flexible than that of SG, but the operation is more complex that needs matrix manipulation. The SG smoothing algorithm is simple and the execution time of the code is short. ConclusionThe smoothing methods and parameters should be selected in accordance with actual conditions to maintain good smoothness and correlation coefficient for spectrum smoothing.关键词：Spectrum smoothing;Smoothness;Correlation coefficient;Matlab GUI
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发布时间：2021-05-19 - 摘要：BackgroundPositron annihilation lifetime measurement as a typical time measuring method of nuclear physics, its time resolution and coincidence count rate are the most important performance parameters. The main factors that determine the time resolution of the spectrometer are the time response of the scintillation crystal and the photoelectric conversion device of the detector, and the coincidence count rate depends not only on the detection efficiency of the detector but also on the judgment method of the time signals by the electronic system. PurposeThis paper aims to find a novel method for improving the utilization rate of detector signals and the coincidence count rate of positron annihilation lifetime measurement effectively. MethodsThe detector signals were divided into two same parts by splitters. One part of the signals was applied to generate an external triggering signal by performing a logic disjunction (OR) operation on the start-signal components to trigger the digitizer for acquiring the other part of signals. Two time interval measurement units which are used for timing, time interval calculation and data statistics were set. To verify the feasibility of this method, the digital storage oscilloscope was used. ResultsMeasurement results showed that, the timing resolution of this testing system is 222 ps. Positron annihilation short lifetime τ1 for sample pure Fe is about 108 ps and the long lifetime τ3 for HDPE is about 2.4 ns. And compared with the conventional measurement, this method gave double the coincidence count rate approximately. ConclusionsIn the conventional measurement, regardless of which detector is used as start-detector or stop-detector, it doesn't influence the measured positron annihilation lifetime spectrum. By using the logic OR operation on the start-signal components of two detectors for triggering, the coincidence count rate will be improved effectively, however, the time resolution and positron annihilation lifetime spectrum or its peak-to-valley are uninfluenced. And each detector can be regarded as a start-detector and the stop-detector.关键词：Positron annihilation lifetime spectrum;Start-signal;Trigger and judgment method;Coincidence count rate
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发布时间：2021-05-19
NUCLEAR ELECTRONICS AND INSTRUMENTATION
- 摘要：BackgroundAt present, high-precision fission nuclear data of fast neutron-induced 239Pu(n, f) reaction is required for the study of new-generation nuclear systems. PurposeBased on the proposed Potential-driving model in the earlier study, the calculation and simulation methods are developed to predict the fission product data for239Pu(n, f) reaction in this paper. MethodsThe driving potential distribution and pre-neutron-emission mass distribution for 239Pu(n, f) reaction are calculated based on the Potential-driving model. In addition, the Potential-driving model is implanted in the GEANT4 code for simulating the physical process of 239Pu(n, f) reaction. The mass distribution and the charge distribution of independent and cumulative yield, the fission-fragment kinetic energy distribution and the fission neutron spectrum of post-neutron-emission for D-T neutron-induced 239Pu(n, f) reaction are presented. Average total kinetic energy of the fission-fragment for 239Pu(n, f) reaction as a function of the incident neutron energy is also shown. ResultsThe calculated and simulated results in the Potential-driving model are compared with the experimental data, the evaluated data from ENDF/B-Ⅶ.1 and the simulated data based on the G4ParaFissionModel. It is found that the results calculated by the Potential-driving model are in good agreement with the experimental data and the ENDF/B-Ⅶ.1 evaluated data, are better than those data calculated by the G4ParaFissionModel. ConclusionsThe Potential-driving model can well describe the post-fission physical process for 239Pu(n, f) reaction. It is a more reliable method for the study on fission-product nuclear data of fast neutron-induced 239Pu(n, f) reaction.关键词：Potential-driving model;Neutron-induced 239Pu (n, f) reaction;Yield distribution;Kinetic energy distribution;Fission neutron spectrum
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发布时间：2021-05-19 - 摘要：BackgroundDynamic behavior is one of the most critical issues for proton exchange membrane fuel cells. PurposeThis study aims to understand the dynamic characteristics which is conducive to the rational design and control of fuel cells. MethodsIn this paper, a simplified modeling of the direct channel proton exchange membrane fuel cell is carried out, and the appropriate parameters are selected for numerical calculation. Response of fuel cells is analyzed in different load time and load amplitude numerically. ResultsThe trend curves of loading amplitude, loading time and reaction gas concentration are obtained. ConclusionThe results show that it is beneficial to improve the stability of fuel cell by increasing the load time and decreasing the load amplitude. And it takes less time to reach stability for the cathode than the anode when the load is changed.关键词：Dynamic loading;Fuel cells;Battery stability;Numerical simulation
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发布时间：2021-05-19 - 摘要：BackgroundThe 232Th(n, 2n) reaction dominates the neutron generation, so the validity of the cross section data is significant in the thorium based reactor. PurposeIn order to provide the data reference for the design of thorium based reactor, an integral experiment to measure the 232Th(n, 2n) reaction rate was carried out using the activation method in a polyethylene shell with DT neutrons. MethodsIn the experiment, thorium samples were arranged in the 0° direction to the incident D+ beam, and a Au-Si surface barrier detector was used to monitor the neutron yield and the fluctuation of neutron flux. ResultsAfter irradiation, the 84.2 keV γ ray emitted from 231Th was measured by HPGe spectrometer, and the 232Th(n, 2n) reaction rate was then obtained. The thorium sample was in foil and powder respectively to eliminate the effect of the sample condition. Simultaneously, the experiment was simulated precisely using Monte Carlo N Particle Transport Code (MCNP) code in the ENDF/B-Ⅶ.1, ENDF/B-Ⅶ.0, and JENDL4.0 libraries. ConclusionThe calculated values in the JENDL4.0 were in good agreement with the experimental ones, which can provide reference for the design of thorium based reactors.关键词：232Th(n, 2n) reaction rate;Neutron integral experiment;D-T neutrons;MCNP;Activation method
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发布时间：2021-05-19
NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH
- 摘要：BackgroundPu is an important material for nuclear industry, its structure is sensitive to temperature, and irradiation has an important impact on it. PurposeIn order to explore the thermodynamic effects of irradiation on plutonium, the phase diagram of pure Pu under the irradiation established in this study provides important theoretical guidance for the design of Pu-based nuclear fuels. MethodsBased on Gibbs free energy of pure Pu, the thermodynamic model of Pu under irradiation was established by considering the excess free energy of vacancies under irradiation conditions. ResultsThe Gibbs free energy function under different irradiation was calculated, and the phase diagrams of pure Pu under different irradiation intensities were obtained. The effects of different irradiation conditions and irradiation time on the stability of six allotropic phases were analyzed. ConclusionThe results indicated that irradiation has great influence on the phase stability of plutonium at lower temperature and the stable phase region of γ-Pu appears near room temperature. Its stable temperature range increased with the increase of the intensity of irradiation and time.关键词：Plutonium;Irradiation;Phase stability;Thermodynamics
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发布时间：2021-05-19 - 摘要：BackgroundThe dynamic tuning of a radio frequency quadrupole (RFQ) is generally achieved via thermal regulation over the vanes and walls. However it takes tens of minutes to reach nominal power. PurposeThe dynamic tracking of the RFQ's resonant frequency and the amplitude-phase feedback control will make it possible for the RFQ to be powered and form an acceleration field quickly, even though the cooling water of the RFQ does not reach thermal equilibrium. MethodsAn RFQ low-level control system implemented with direct digital synthesis (DDS) and phase-locked loop (PLL) technology was designed and tested at an experimental platform based on a simulation cavity. ResultsThe test results show that this scheme can achieve the tracking of resonant frequency with ±0.5% amplitude stability and ±0.5° phase stability. ConclusionThe performance of system meets expectation, and reaches acquired accuracy.关键词：RFQ;Low level radio frequency (LLRF);Field Programmable Gate Array (FPGA);DDS
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发布时间：2021-05-19 - 摘要：BackgroundWith the development of radiation technology, it needs to improve the accuracy of dose simulation. PurposeBuild up a simplified benchmarking procedure to determine the incident electron beam parameters independently using a Monte Carlo linear accelerator model. MethodsA 10 cm×10 cm field is simulated to acquire the parameters influence on the dose distributions for Varian Ⅸ 6 MV megavoltage electron beams. ResultsThe calculated depth doses had no significant changes when the electron mean energy and radial intensity varied in 5.5~6.4 MeV and 0.1~0.4 cm respectively. And the dose profile simulated with an electron radial intensity in 0~0.19 cm had a good agreement with the measured dose profile in the main field while obvious discrepancies in the penumbra region. The mean angular spread was found to be 0.3° to get good matching between calculations and measurements at all considered depths. ConclusionAccurate dose distributions are achieved by using the incident electron beam parameters benchmarked with the proposed procedure. As the percentage depth doses and dose profiles are insensitive to the electron energy and radial intensity correspondingly, they are feasible to benchmark individually.关键词：Monte Carlo;Electron beam parameters;Percentage depth doses;Dose profiles
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发布时间：2021-05-19
LOW ENERGY ACCELERATOR, RAY AND APPLICATIONS
- 摘要：BackgroundMolten salt reactor is one of the six Generation Ⅳ advanced reactor concepts selected by Generation Ⅳ International Forum (GIF), which can be divided into liquid-fueled and solid-fueled molten salt reactor. The solid-fueled molten salt reactor uses high-temperature liquid-salt as coolant and is provided with features of high-temperature, low-pressure and high-power density, as well as great advantage and potential in inherent safety. PurposeThis study aims to develop and validate a three-dimensional time-spatial kinetics code named TCORE3D-HEX which can be used to carry out transient analysis and safety assessment of molten salt-cooled reactor with hexagonal fuel assembly. MethodsThe exponential transform and hexagonal nodal expand methods are applied in the TCORE3D-HEX kinetics code. Two VVER (Vodo-Vodyanoi Energetichesky Reaktor) international benchmarks are selected to validate the validity of the TCORE3D-HEX code by comparing with several three-dimensional hexagonal nodal time-spatial kinetics codes. ResultsThe results indicate that the numerical result of the TCORE3D-HEX code are in good agreement with that of other kinetics codes. ConclusionThe developed kinetics code is validated on VVER pressurized water reactor (PWR), and will be a reliable analytical and assessment tool for the design of innovative molten salt-cooled reactor in thorium molten salt reactor (TMSR).关键词：Molten salt-cooled reactor;Exponential transform;Hexagonal nodal method;Time-spatial kinetics
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发布时间：2021-05-19 - 摘要：BackgroundIn molten salt reactor, the graphite can adsorb a mass of tritium. Fluorine is a constituent of molten salt, and neutron irradiation can induce a number of defects on the graphite in molten salt reactor. It is necessary to study the influence of fluorine and the defects of the graphite on tritium adsorption in molten salt reactor. PurposeThis study aims to reveal the influence mechanism of fluorine and monovacancy defect on tritium adsorption on graphite surface. MethodsSimulation study of the adsorption behaviors of hydrogen, fluorine and hydrogen fluoride on the surfaces of perfect graphene and vacancy-defected graphene were carried out by using first-principles calculations. ResultsThe results indicate that fluorine preferentially bonds with carbon atoms when hydrogen and fluorine exist at the same time. The monovacancy on graphite surface prompts hydrogen fluoride molecule to dissolve and bond with carbon atom. Moreover, the graphite surface can be distorted after adsorbing hydrogen and fluorine. ConclusionTritium generated from the molten salt reactor will be preferentially adsorbed and accumulate in the regions with more reactive activities such as monovacancy.关键词：Tritium;Fluorine;Graphite;Adsorption;First-principles calculation;Molten salt reactor
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发布时间：2021-05-19 - 摘要：BackgroundNaNO3-KNO3-NaNO2 (7%-53%-40% in mass fraction) Hitec molten salt is considered as one of the promising candidate materials for heat transfer and thermal storage media in concentrated solar power (CSP), due to wide work temperature, low vapor pressure and so on. However, the specific thermal capacity of molten salt is relatively low. It will be significant in practical applications by improving the species thermal capacity with some addition into molten salt. PurposeThe study aims to investigate the effect of various size (25 nm, 40 nm and 100 nm) and addition amount (0.062 5%, 0.5% and 1% in mass fraction) of TiO2 nanoparticle on the thermal storage properties of Hitec molten salt. MethodsDifferential scanning calorimetry, thermal gravity and laser flash analyzer were used to determine the effect of TiO2 nanoparticle on the species heat capacity, thermal stability and thermal conductivity of Hitec. Results & ConclusionThe TiO2 nanoparticle improves the thermal storage properties of Hitec, compared to origin Hitec. Furthermore, 0.062 5% (mass fraction) addition of TiO2 nanoparticle with 25 nm size showed the best enhancement of the thermal storage properties of Hitec, where the specific heat capacity and thermal conductivity increased by 12% and 15%, respectively. Moreover, the upper working temperature of NaNO3-KNO3-NaNO2 increased a lot.关键词：Hitec molten salt;Thermal energy storage;Specific heat capacity;Thermal conductivity;Thermal stability
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发布时间：2021-05-19 - 摘要：BackgroundIn the design of nuclear reactor, it is significant to determine the parameters of secondary neutron source. PurposeThe aim of this paper is to elaborate a calculation method for parameters of secondary neutron source systematically. MethodsFirstly, compositions of the fuel and secondary neutron source were generated by depletion calculation. Then, gamma production and photonuclear reaction in secondary neutron source were simulated. Specific parameters of secondary neutron source, such as source strength, energy spectrum and space distribution, have been obtained. ResultsThe parameters of secondary neutron source have been used to calculate the response of detectors outside the core. The results are in agreement with the measurements. ConclusionThe calculation method suggested in this paper is available.关键词：Secondary neutron source;Parameters of neutron source;Criticality safety
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发布时间：2021-05-19 - 摘要：BackgroundThe molten salt frozen-wall technique is effective to protect the equipment involved during dry reprocessing of spent nuclear fuel in the molten salt reactor from chemical corrosion (serious corrosion). PurposeThe thickness of frozen wall and the temperature distribution of the molten salt have a great influence on the protective effect and related dry processing parameters. MethodsBased on the central cooled experimental apparatus of frozen wall, the maintenance of the frozen wall was carried out using FLiNaK molten salt medium. ResultsThe thickness of the frozen wall and the distribution of temperature in reactor were obtained by the method of air cooling in the center of the cylinder. The heat transfer equilibrium condition of the frozen wall was calculated by numerical simulation, the computed results agreed well with the experimental results. ConclusionThe experimental conditions for suitable thickness of frozen wall were obtained. The control technology of the frozen wall thickness and temperature field distribution can provide reference for the design of vessel with frozen wall.关键词：Frozen wall;Dry reprocessing;Molten salt reactor
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发布时间：2021-05-19
NUCLEAR ENERGY SCIENCE AND ENGINEERING
- 摘要：BackgroundThe separation and cyclic utilization of thorium is an important part of thorium-uranium fuel cycle for molten salt reactor. Therefore, separation of thorium from fission products, especially lanthanides, is the key step to electrochemical separation of thorium in molten salt because of their similar chemical properties. PurposeThe aim of this work is to explore the influence of fluorine ion (F-) on electrochemical properties of 5 lanthanides in LnF3-LiCl-KCl molten salt and to confirm the feasibility of electrochemical separation of thorium from lanthanides in chloride molten salt. MethodsTransient electrochemical techniques such as cyclic voltammetry and square wave voltammetry were employed to investigate the reduction mechanism and diffusion coefficient of Ln ions on a tungsten inert electrode. ResultsIn LnF3-LiCl-KCl molten salt, Ce3+ and Gd3+ were reduced into metal Ce and Gd according to a one-step process by exchanging 3 electrons; Nd3+ was reduced into metal Nd through two steps; Sm3+ and Eu3+ couldn't be reduced into metal in tungsten electrode, and both of them were transformed into divalent state. The existence of F-would not change the electrode reaction process of Ln cations. The differences of deposition potential between Th and the 5 Lns on inert electrode were larger than 0.19 V, which demonstrated theoretically that it was feasible to separate Th from Lns in LiCl-KCl molten salt. Compared with pure chloride molten salt, the existence of F-decreased the activity of Ln3+, resulting in the decrease of diffusion efficiency of all Ln ions. ConclusionThe study provided experimental foundation for feasibility investigation of the separation of thorium fluoride from lanthanides fluoride in LiCl-KCl molten salt.关键词：LnF3-LiCl-KCl;Cyclic voltammetry;Square wave voltammetry;Electrode process;Diffusion efficient
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发布时间：2021-05-19
NUCLEAR CHEMISTRY, RADIOCHEMISTRY, RADIOPHARMACEUTICALS AND NUCLEAR MEDICINE
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