Preliminary study on CAD-based method of characteristics for neutron transport calculation

Our new method makes use of a CAD-based automatic modeling tool, MCAM, for geometry modeling and ray tracing of particle transport in method of characteristics （MOC）. It was found that it could considerably enhance the capability of MOC to deal with more complicated models for neutron transport calculation. In our study, the diamond-difference scheme was applied to MOC to reduce the spatial discretization errors of the fiat flux approximation. Based on MCAM and MOC, a new 2D MOC code was developed and integrated into the SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical results demonstrated the feasibility and effectiveness of the new method for neutron transport calculation in MOC.     

Preliminary study on CAD-based method of characteristics for neutron transport calculation

Our new method makes use of a CAD-based automatic modeling tool, MCAM, for geometry modeling and ray tracing of particle transport in method of characteristics (MOC). It was found that it could considerably enhance the capability of MOC to deal with more complicated models for neutron transport calculation. In our study, the diamond-difference scheme was applied to MOC to reduce the spatial discretization errors of the flat flux approximation. Based on MCAM and MOC, a new 2D MOC code was developed and integrated into the SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical results demonstrated the feasibility and effectiveness of the new method for neutron transport calculation in MOC.     

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation

Two-dimensional finite element mesh generation algorithm for electromagnetic field calculation is proposed in this paper to improve the efficiency and accuracy of electromagnetic calculation. An image boundary extraction algorithm is developed to map the image on the geometric domain. Identification algorithm for the location of nodes in polygon area is proposed to determine the state of the node. To promote the average quality of the mesh and the efficiency of mesh generation, a novel force-based mesh smoothing algorithm is proposed. One test case and a typical electromagnetic calculation are used to testify the effectiveness and efficiency of the proposed algorithm. The results demonstrate that the proposed algorithm can produce a high-quality mesh with less iteration.     

Determination of event start time at BESⅢ

The principle of the method for the BESⅢ event start time determination and the code construction are described. The investigation of influence of the noise, the method of rejecting noise and the performance checking by the Monte Carlo physics data sample are also presented. The preliminary results got from the Monte Carlo simulation are presented, the reconstruction efficiency of J/ψ→ anything events at noise level 0~60% can achieve above 99%, and the error rate is below 1%.     

An element-free Galerkin （EFG） method for numerical solution of the coupled Schrodinger-KdV equations

The present paper deals with the numerical solution of the coupled Schrodinger-KdV equations using the elementfree Galerkin （EFG） method which is based on the moving least-square approximation. Instead of traditional mesh oriented methods such as the finite difference method （FDM） and the finite element method （FEM）, this method needs only scattered nodes in the domain. For this scheme, a variational method is used to obtain discrete equations and the essential boundary conditions are enforced by the penalty method. In numerical experiments, the results are presented and compared with the findings of the finite element method, the radial basis functions method, and an analytical solution to confirm the good accuracy of the presented scheme.     

An element-free Galerkin(EFG) method for numerical solution of the coupled Schrdinger-KdV equations

The present paper deals with the numerical solution of the coupled Schrdinger-KdV equations using the elementfree Galerkin(EFG) method which is based on the moving least-square approximation.Instead of traditional mesh oriented methods such as the finite difference method(FDM) and the finite element method(FEM),this method needs only scattered nodes in the domain.For this scheme,a variational method is used to obtain discrete equations and the essential boundary conditions are enforced by the penalty method.In numerical experiments,the results are presented and compared with the findings of the finite element method,the radial basis functions method,and an analytical solution to confirm the good accuracy of the presented scheme.     

A complex variable meshless method for fracture problems

1 Introduction The meshless (or meshfree) method has been a hot topic and the development trend of numerical methods for many science and engineering problems in recent years. Comparing with the conventional numerical methods, such as the finite element method and the boundary element method, the meshless method is an approximation based on nodes, and does not form a mesh to determine the shape function in the domain, in which a problem is to be solved. The meshless method has some advantages …     

Noise Shielding Using Acoustic Metamaterials

We exploit theoretically a class of rectangular cylindrical devices for noise shielding by using acoustic metamateriais. The function of noise shielding is justified by both the far-field and near-field full-wave simulations based on the finite element method. The enlargement of equivalent acoustic scattering cross sections is revealed to be the physical mechanism for this function. This work makes it possible to design a window with both noise shielding and air flow.     

Simulation study on the boron-coated GEM neutron beam monitor

A Monte Carlo method of the 3D GEM simulation is introduced.The physical process of the neutron detection is described with the Geant4 code and the Garfield code.The results of the optimized electric-fields,the emitted ions spectrum,the electrons transverse diffusion and the signal width are presented.Moreover,the preliminary result with a CF-252 neutron source is reported.These are useful in designing detector structures and to provide an optimized option for the development of the boron-coated GEM neutron beam monitor.     

An optical fiber spool for laser stabilization with reduced acceleration sensitivity to 10~(-12)/g

Environmental vibration causes mechanical deformation in optical fibers, which induces excess frequency noise in fiber-stabilized lasers. In order to solve such a problem, we propose an ultralow acceleration sensitivity fiber spool with symmetrically mounted structure. By numerical analysis with the finite element method, we obtain the optimal geometry parameters of the spool with which the horizontal and vertical acceleration sensitivity can be reduced to 3.25 × 10-12/g and 5.38 × 10-12/g respectively. Moreover, the structure features the insensitivity to the variation of geometry parameters,which will minimize the influence from numerical simulation error and manufacture tolerance.     

全堆芯Pin by Pin中子扩散节块法CMFD加速

采用节块方法中有效的半解析方法求解中子扩散方程，在径向采用pin by pin的计算方式且中子通量基于两阶展开，在轴向采用基于4阶展开中子通量的节块法，并且进行全堆粗网有限差分（CMFD）加速，以达到计算精度与计算效率的平衡.通过IAEA 2D/3D基准问题和自定义3D pin by pin参考问题的数值计算，验证所提出的方法能够达到预期的精度，同时CMFD能够取得很好的加速效果.     

JMCT与子通道程序耦合方法研究及验证

蒙特卡罗与热工水力的耦合计算是目前反应堆数值模拟的重要研究方向,在蒙特卡罗方法连续能量点截面的基础上结合热工程序的温度反馈,反应堆中子计算的准确性得到大幅提高。为了提高计算精度,堆芯模型分辨率也需进一步提高,相比于组件均匀化模型,pin-by-pin的建模方式能够获得更好的结果。利用蒙特卡罗程序JMCT与子通道程序COBRA-EN实现了蒙特卡罗-热工的内耦合,内耦合方式通过内存进行数据传递,其计算效率及安全性均优于外耦合方法。随后利用NURISP项目迷你堆的pin-by-pin模型对耦合程序进行验证。计算结果与同类耦合程序相似,验证了程序的准确性。同时,对耦合过程的收敛性问题进行了初步分析。     

基于VENUS-III国际基准模型的JMCT程序验证

基于自主研制的三维中子-光子耦合输运蒙特卡罗通用程序JMCT（J Monte Carlo Transport Code）,采用连续点截面,对国际基准屏蔽VENUS-III模型开展精细建模和中子输运临界及屏蔽计算.临界计算得到系统k_eff、重要区域的通量及能谱.结果表明,JMCT和MCNP程序的重要区域体通量计数吻合较好,偏差均在1%以内.深穿透屏蔽计算采用外源模式,点探测器计数,JMCT计算值与实验测量值偏差在15%以内,满足屏蔽设计对误差的要求.初步验证了JMCT程序临界及屏蔽计算的可用性.     

基于平面通量展开的三维Pin by Pin输运SP3计算

基于Pin by Pin输运SP₃计算是下一代反应堆物理计算方法中一个重要的研究方向。节块法一般采用高阶通量和中子源展开以适应较大的节块尺寸,因此对于Pin by Pin计算来说效率偏低。由于反应堆堆芯不均匀性更多发生在径向,本文提出一种径向基于二维平面通量展开结合轴向常规节块法的综合方法进行三维Pin by Pin输运SP₃计算,其三个方向的节块耦合迭代均采用基于中子净流耦合的格式。通过IAEA 2D/3D基准问题和典型输运基准问题计算,验证该计算方法对于堆芯扩散计算和输运计算的正确性和可行性。     

基于VERA基准题的cosRMC程序验证

为了验证反应堆物理软件和方法的计算能力,美国CASL (Consortium for Advanced Simulation of LWRs) 项目提出了VERA (Virtual Environment for Reactor Application) 堆芯物理基准题。该基准题以Watts Bar初始堆芯为模型,涵盖从二维单栅元到三维全堆芯的燃耗及换料的十个基准问题。针对VERA基准题模型,利用COSINE软件包中的反应堆蒙特卡罗分析程序cosRMC进行临界计算,得到了有效增殖因子、组件功率分布、控制棒微积分价值和反应性系数等结果。通过与基准题中提供的KENO结果对比,两种蒙特卡罗程序的计算结果吻合良好。这表明cosRMC程序具有从组件到堆芯的计算能力,其临界计算精度基本与KENO程序相当。     

Dragon程序在金属燃料铅铋快堆堆芯计算中的应用与偏差分析

铅铋合金或铅冷却快堆（LFR）是具有良好应用前景的第四代先进核能系统之一。针对环形芯体金属燃料（UZr，UPuZr）LFR的燃料组件与堆芯，利用Dragon/Donjon程序开展中子学计算，获得了基于ENDF/B 8.0库的172群和295群多群中子数据库、输运方法（SP3）和扩散方法（MCFD）的结果及其与蒙卡程序RMC的偏差。采用SP3算法针对UZr燃料得到的k_eff偏差小于550×10?5；对于UPuZr燃料采用MCFD算法得到的k_eff偏差小于?700×10?5。控制棒组件价值的偏差小于7.6%；172群和295群库的结果基本无差异。应用SP3算法的燃料组件功率偏差小于±6.0%；SP3算法的偏差小于MCFD的。结果证明，Dragon/Donjon程序在金属燃料铅铋快堆物理分析中具有可行性。     

大型压水堆装载50%MOX燃料方案压力容器辐照安全计算

对含MOX燃料堆芯的压力容器(RPV)快中子注量率计算进行了初步研究,探讨了适用于MOX堆芯方案屏蔽计算的堆芯源项处理方法。采用三维离散纵标程序TORT,针对CAP1400型堆芯装载50%MOX燃料方案开展了RPV快中子注量计算,结果表明:堆芯装载50%MOX燃料可满足RPV屏蔽安全设计要求;对比分析含MOX堆芯方案和全UO2堆芯方案的RPV快中子注量率的特性差异,从RPV辐射防护最优化的角度,后续燃料管理方案优化时可重点关注关键位置处组件的布置。     

蒙特卡罗粒子输运软件JMCT的网格计数功能设计与实现

基于蒙特卡罗输运的网格计数能够统计指定区域内密集的分布计数量.为实现JMCT统计局部计数量分布,设计并实现了JMCT网格计数功能,该功能支持三种正交几何（xyz直角几何、rθz柱几何、rθφ球几何）的均匀及不均匀剖分;介绍xyz直角几何网格计数的算法;基于大亚湾反应堆pin-by-pin模型、Venus模型以及ITER次临界包层模型等初步验证了网格计数功能;应用铀阵列模型,采用若干种网格剖分办法,在单机上对比测试了xyz直角几何下JMCT和MCNP5网格计数功能的串行性能,结果显示JMCT的计数时间较短,具有较高的效率.     

节块内嵌离散纵标(SN)方法的算法研究及程序开发

介绍节块内嵌离散纵标(S_N)方法求解三维堆芯中子输运/扩散方程的算法框架.在基于扩散理论的三维粗网节块展开方法(NEM)的算法体系中,用基于输运理论的径向二维细网节块离散纵标方法(NDOM)的内迭代过程,替代节块展开方法(NEM)内迭代的径向求解过程.该算法充分考虑了核电厂反应堆堆芯的三维结构特点,另一方面,也充分利用了已经成熟的三维粗网节块展开方法(NEM)和二维离散纵标方法(S_N)的研究成果,同时有效避免了利用离散纵标方法(S_N)求解三维中子输运方程所面临的计算内存和计算时间的瓶颈问题.编制开发二维多群节块离散纵标方法(NDOM)模块程序NS_NM和三维多群节块展开方法(NEM)模块程序MGNEM,并以此为基础编制开发节块内嵌S_N方法的模块程序HANWIND;其中,NS_NM为HANWIND求解两维问题的功能模块.针对OECD/NEA-2D C5G7MOX基准问题以及两环路核电厂三维堆芯的数值验算结果表明,节块内嵌S_N方法的算法开发及程序编制有效、切实可行.     

高温气冷堆堆芯中子时空动力学模拟计算

研究开发三维圆柱几何堆芯多群中子时空动力学改进准静态方法模拟计算程序.对给定的模块式高温气冷堆模型进行模拟计算.初始状态下,计算结果与中子扩散程序CITATION吻合很好.动态情况下,模拟堆芯反应性、堆内各能群中子平均注量率和堆芯相对功率等物理量随时间变化,计算结果与理论分析一致.