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A meshless local Petrov–Galerkin method for solving the neutron diffusion equation

Nuclear Science and Techniques 2018年第11期29卷 304-322页

作者： Shima Tayefi Ali Pazirandeh Mohsen Kheradmand Saadi Department of Nuclear Engineering Science and Research BranchIslamic Azad University

The goal of this study is to solve the neutron diffusion equation by using a meshless method and evaluate its performance compared to traditional methods. This paper proposes a novel method based on coupling the meshless local Petrov–Galerkin approach and the moving least squares approximation. This computational procedure consists of two main steps. The first involved applying the moving least squares approximation to construct the shape function based on the problem domain. Then, the obtained shape function was used in the meshless local Petrov–Galerkin method to solve the neutron diffusion equation.Because the meshless method is based on eliminating the mesh-based topologies, the problem domain was represented by a set of arbitrarily distributed nodes. There is no need to use meshes or elements for field variable interpolation. The process of node generation is simply and fully automated, which can save time. As this method is a local weak form, it does not require any background integration cells and all integrations are performed locally over small quadrature domains. To evaluate the proposed method,several problems were considered. The results were compared with those obtained from the analytical solution and a Galerkin finite element method. In addition, the proposed method was used to solve neutronic calculations in thesmall modular reactor. The results were compared with those of the citation code and reference values. The accuracy and precision of the proposed method were acceptable. Additionally, adding the number of nodes and selecting an appropriate weight function improved the performance of the meshless local Petrov–Galerkin method. Therefore, the proposed method represents an accurate and alternative method for calculating core neutronic parameters.

关键词： neutron diffusion equation Meshless local Petrov–Galerkin(MLPG) Moving least squares approximation(MLSA) Meshless methods

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Characterization of a new shielding rubber for use in neutron–gamma mixed fields

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Nuclear Science and Techniques 2018年第3期29卷 78-85页

作者： M.Salimi N.Ghal-Eh E.Asadi Amirabadi School of Physics Damghan UniversityP.O.Box 36716-41167DamghanIran Department of Physics School of SciencesFerdowsi University of MashhadP.O.Box 91775-1436MashhadIran Laser-Plasma Research Institute Shahid Beheshti UniversityP.O.Box 19839-63113TehranIran

A variety of formulations was investigated for the fabrication of an appropriate shielding rubber to be used in neutron–gamma mixed fields. Having considered the required mechanical properties together with tungsten as the gamma-ray absorbing element, calculations with MCNPX 2.6 code confirmed that the incorporation of 5 weight percentage(wt%) of boron carbide exhibited the best performance as a thermal neutron absorber. A series of both experimental and simulation results are provided for comparison.

关键词： Shielding Rubber neutron Gamma MCNPX

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Effect of non-stationary accretion on spectral state transitions:An example of a persistent neutron star LMXB 4U 1636–536

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Research in Astronomy and Astrophysics 2018年第3期18卷 91-98页

作者： Hui Zhang Wen-Fei Yu Key Laboratory for Research in Galaxies and Cosmology Shanghai Astronomical ObservatoryChinese Academy of Sciences

Observations of black hole and neutron star X-ray binaries show that the luminosity of the hard-to-soft state transition is usually higher than that of the soft-to-hard state transition,indicating additional parameters other than mass accretion rate are required to interpret spectral state transitions.It has been found in some individual black hole or neutron star soft X-ray transients that the luminosity corresponding to the hard-to-soft state transition is positively correlated with the peak luminosity of the following soft state. In this work,we report the discovery of the same correlation in the single persistent neutron star low mass X-ray binary（LMXB） 4 U 1636–536 based on data from the All Sky Monitor（ASM） on board RXTE,the Gas Slit Camera（GSC） on board MAXI and the Burst Alert Telescope（BAT） on board Swift. We also found such a positive correlation holds in this persistent neutron star LMXB in a luminosity range spanning about a factor of four. Our results indicate that non-stationary accretion also plays an important role in driving X-ray spectral state transitions in persistent accreting systems with small accretion flares,which is much less dramatic compared with the bright outbursts seen in many Galactic LMXB transients.

关键词： accretion accretion disks - X-rays binaries - stars neutron

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Geant4 simulation of 238U(n,f) reaction induced by D-T neutron source

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Nuclear Science and Techniques 2017年第1期28卷 49-56页

作者： Chang-Lin Lan Meng Peng Yi Zhang Zheng Wei Ze-En Yao Bao-Lin Xie School of Nuclear Science and Technology Lanzhou University Lanzhou 730000 China Key Laboratory of Special Function Materials and Structure Design Ministry of Education Lanzhou 730000 China

Knowledge of actinides(n,f) fission process induced by neutron is of importance in the field of nuclear power and nuclear engineering,especially for reactor applications.In this work,fission characteristics of^(238)U(n,f) reaction induced by D-T neutron source were simulated with Geant4 code from multiple perspectives,including the fission production yields,total nubar,kinetic energy distribution,fission neutron spectrum and cumulative γ-ray spectrum of the fission products.The simulation results agree well with the experimental nuclear reaction data(EXFOR) and evaluated nuclear data(ENDF).Mainly,this work was to examine the rationality of the parametric nuclear fission model in Geant4 and to direct our future experimental measurements for the cumulative fission yields of ^(238)U(n,f) reaction.

关键词： Fission characteristics Geant4 code 238U(n,f) reaction D-T neutron source Decayed c-ray spectrum

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Visualization and quantification of water movement in porous cement-based materials by real time thermal neutron radiography:Theoretical analysis and experimental study

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Science China(Technological Sciences) 2010年第5期53卷 1198-1207页

作者： ZHANG Peng1,WITTMANN F H1,2,ZHAO TieJun1,LEHMANN E3 & JIN ZuQuan1 1 Center for Durability & Sustainability Studies of Shandong Province,Qingdao Technological University,Qingdao 266033,China 2 Aedificat Institute Freiburg,Freiburg D-79100,Germany 3 Department of Spallation neutron Source(ASQ),Paul Scherrer Institute,Villigen PSI CH-5232,Switzerland Center for Durability & Sustainability Studies of Shandong Province Qingdao Technological University Qingdao China Aedificat Institute Freiburg Freiburg Germany Department of Spallation neutron Source (ASQ) Paul Scherrer Institute Villigen PSI Switzerland

Water movement in porous cement-based materials is of great importance when studying their deterioration processes and durability.Many traditional methods based on mass changes,electricity or nuclear magnetic resonances are available for studying water transport in cement-based materials.In this research,an advanced technique i.***.thermal neutron radiography was utilized to achieve visualization and quantification of time dependent water movement including water penetration and moisture vapor in porous cement-based materials through theoretical analysis and experimental study.Because thermal neutrons ex-perience a strong attenuation by hydrogen,neutron radiography exhibits high sensitivity to small amounts of water.A neutron transmission analysis for quantitative evaluation of raw radiographic measurements was developed and optimized based on point scattered functions(PScF).The determinations of the real time and space dependent water penetration into uncracked and cracked mortar samples,as well as the drying process have been presented in this paper.It is illustrated that thermal neutron radiography can be a useful research tool for visualization and quantification of water movement in porous building materials.The obtained results will help us to better understand deteriorating processes of cement-based materials and to find ways to improve their durability.

关键词： thermal neutron radiography visualization quantification water penetration moisture diffusion cement-based materials

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Calculation of thermal neutron albedo for mono-material and bi-material reflectors

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Nuclear Science and Techniques 2018年第9期29卷 185-191页

作者： Sara Azimkhani Farhad Zolfagharpour Farhood Ziaie Department of Physics University of Mohaghegh Ardabili Radiation Application Research School Nuclear Science & Technology Research Institute

Thermal neutron albedo has been investigated for different thicknesses of mono-material and bi-material reflectors. An equation has been obtained for a bi-material reflector by considering the neutron diffusion equation. The bi-material reflector consists of binary combinations of water, graphite, lead, and polyethylene. An experimental measurement of thermal neutron albedo has also been conducted for mono-material and bi-material reflectors by using a^(241) Am–Be(5.2 Ci) neutron source and a BF3 detector. The maximum value of thermal neutron albedo was obtained for a polyethylene–water combination(0.95 ± 0.02).

关键词： neutron current Bi-material reflector Thermal neutron albedo BF3 detector Reflection Diffusion equation

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Preparation and verification of mixed high-energy neutron crosssection library for ADS

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Nuclear Science and Techniques 2018年第10期29卷 163-170页

作者： Ze-Long Zhao Yong-Wei Yang Hai-Yan Meng Qing-Yu Gao Yu-Cui Gao Institute of Modern Physics Chinese Academy of SciencesLanzhou 730000China University of Chinese Academy of Sciences Beijing 100049China

An accelerator-driven subcritical system(ADS)is driven by an external spallation neutron source, which is generated from a heavy metal spallation target to maintain stable operation of the subcritical core, where the energy of the spallation neutrons can reach several hundred megaelectron volts. However, the upper neutron energy limit of nuclear cross-section databases, which are widely used in critical reactor physics calculations, is generally 20 MeV.This is not suitable for simulating the transport of highenergy spallation neutrons in the ADS. We combine the Japanese JENDL-4.0/HE high-energy evaluation database and the ADS-HE and ADS 2.0 libraries from the International Atomic Energy Agency and process all the data files for nuclides with energies greater than 20 MeV. We use the continuous pointwise cross-section program NJOY2016 to generate the ACE-formatted cross-section data library IMPC-ADS at multiple temperature points. Using the IMPC-ADS library, we calculate 10 critical benchmarks of the International Criticality Safety Benchmark Evaluation Project manual, the 14-MeV fixed-source problem of the Godiva sphere, and the neutron flux of the ADS subcritical core by MCNPX. To verify the correctness of the IMPCADS, the results were compared with those calculated using the ENDF/B-VII.0 library. The results showed thatthe IMPC-ADS is reliable in effective multiplication factor and neutron flux calculations, and it can be applied to physical analysis of the ADS subcritical reactor core.

关键词： Accelerator-driven subcritical system IMPCADS MCNPX NJOY2016 neutron cross section

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Application of Monte Carlo method to calculate the effective delayed neutron fraction in molten salt reactor

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Nuclear Science and Techniques 2019年第2期30卷 143-152页

作者： Gui-Feng Zhu Rui Yan Hong-Hua Peng Rui-Min Ji Shi-He Yu Ya-Fen Liu Jian Tian Bo Xu Shanghai Institute of Applied Physics Chinese Academy of Sciences

Delayed neutron loss is an important parameter in the safety analysis of molten salt reactors. In this study,to obtain the effective delayed neutron fraction under flow condition, a delayed neutron precursor transport was implemented in the Monte Carlo code MCNP. The moltensalt reactor experiment(MSRE) model was used to analyze the reliability of this method. The obtained flow losses of reactivity for 235 U and 233 U fuels in the MSRE are223 pcm and 100.8 pcm, respectively, which are in good agreement with the experimental values(212 pcm and100.5 pcm, respectively). Then, six groups of effective delayed neutron fractions in a small molten salt reactor were calculated under different mass flow rates. The flow loss of reactivity at full power operation is approximately105.6 pcm, which is significantly lower than that of the MSRE due to the longer residence time inside the active core. The sensitivity of the reactivity loss to other factors,such as the residence time inside or outside the core and flow distribution, was evaluated as well. As a conclusion,the sensitivity of the reactivity loss to the residence time inside the core is greater than to other parameters.

关键词： Monte Carlo Effective delayed neutron fraction Molten salt reactor

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Magnetic structure of Pr_6Fe_(13)Ge studied by Mossbauer effect and neutron diffraction

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Science China Mathematics 2000年第11期43卷 1208-1214页

作者：王芳卫张泮霖严启伟宫华扬 State Key Laboratory of Magnetism Institute of Physics and Center for Condensed Matter Physics Chinese Academy of Sciences Beijing 100080 China Institute of High Technology Wuhan Steel and Iron Cooperation Wuhan 430080 China

Magnetic structure of Pr6Fe13Ge at room temperature has been investigated by magnetic measurement, Mossbauer effect and neutron diffraction. Magnetic atoms are closely packed up and down the mirror planes at z = 0 and 1/2 and separated by the non-magnetic atoms located on the planes at z= 1/4 and 3/4, which constructs an M/NM/M sandwich structure (M: magnetic, NM: non-magnetic). The intralayer magnetic moments couple ferromagnetically and are out of ab plane at a small angle so as to form a component along c-axis. The interlayer coupling is antiferromagnetic for the ab component while ferromagnetic for the c component.

关键词： magnetic structure Mossbauer effect neutron diffraction Pr6Fe13Ge.

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Study of Interfering nuclear reactions in determination of platinum group elements by neutron activation analysis

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Science China Mathematics 1998年第5期41卷 551-556页

作者：李晓林柴之芳毛雪瑛 Institute of High Energy Physics Chinese Academy of Sciences Beijing China

Eighteen interfering nuclear reactions that likely occur in neutron activation analysis of platinum group elements are studied. Their degrees are calculated by the basic principle of activation analysis. The calculation results indicate that most of the nuclear interferences become significant only if the interfering elements exist in major amount and the elements of interest in trace amount. However, the second\|order interference to platinum analysis from gold and the fission interference to analysis of ruthenium and palladium from uranium cannot be neglected even if the gold and uranium exist as trace constituents in samples.

关键词： neutron activation analysis platinum group elements nuclear interferences.

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