强各向异性散射中子输运方程加速方法

采用修正的PN方程加速中子输运方程的SN数值求解过程.并将该加速方法应用到国际通用的ANISN程序中,对其进行了数值检验.数值计算结果表明,本文加速方法可以使迭代次数大量减少,特别是对于强各向异性散射问题具有明显的加速效果.     

异构并行的高阶散射特征线方法及其在临界实验装置模拟中的应用

在临界实验装置的物理计算中,由于较厚水反射层的存在,中子各向异性散射会对计算结果有重要影响。基于P1各向异性散射特征线方法(MOC),开发了能够处理各向异性散射的特征线输运计算程序,并实现了高阶散射特征线输运计算的高性能异构并行。为确认程序对临界实验装置的物理计算精度,本文选取LCT011临界实验基准进行堆芯物理计算,并与蒙特卡罗程序进行对比验证。各向异性源使得计算量与内存消耗均有显著增加,给异构系统带来较大的显存负担,因此本文进而对高阶散射输运求解器进行性能分析。数值结果表明：在高阶散射计算条件下,程序可达到蒙特卡罗程序的同等精度,且具有较高的计算效率。     

特征线方向概率方法与性能分析模型研究

为了进一步提高特征线方向概率方法(CDP)的计算效率,提出了一种角度相关的边界均匀化方法。提出CDP性能分析模型,显性地比较分析特征线方法(MOC)和CDP的计算效率。数值结果表明,所提模型正确,并显示出CDP在计算效率方面的优势。     

特征线几何预处理方法比较

网格划分、特征线间距、角度求积组、极角数目和方位角大小等几何预处理过程对特征线法的计算精度和计算效率有较大影响。基于步特征线法开发输运程序,通过数值计算验证所开发程序的正确性并分析两种特征线扫描方法(首尾相间循环扫描法、首尾相接循环扫描法)以及网格划分、特征线间距、角度求积组、极角数目、方位角大小对计算精度的影响。结果表明,开发的程序准确可靠;首尾相间循环扫描方法的收敛速度比首尾相接循环扫描方法慢。     

提高三维特征线方法计算速度的初步研究

反应堆物理计算的发展要求进行三维复杂几何的输运计算,特征线方法可以满足这些要求,在实际中的应用中因收敛缓慢和计算时间过长而受到限制。本文结合现有数值加速手段和计算机硬件发展,提出双重广义粗网有限差分加速方法和角度分组的角度并行方法,并将这2种方法应用于三维特征线程序(TCM)中。通过多个基准题进行数值验证,计算结果表明方法在保证计算精度的前提下,可有效缩短原有程序的计算时间。     

GPU加速三维特征线方法的研究

三维特征线方法可以精确求解任意几何堆芯的稳态多群中子输运方程,但同时也具有收敛慢、计算时间长的不足,需要研究相应的加速手段.图形处理器(GPU)计算由于具有速度快,能耗低的优点,被认为是未来高性能计算发展的方向之一.研究GPU计算加速三维特征线方法,并将其应用到三维特征线程序TCM中.借助统一计算设备架构(CUDA)的GPU计算,中央处理器(CPU)负责内存分配、有效增殖系数keff和源分布计算等逻辑性强或归约计算的处理,GPU执行特征线射线扫描细网求解细网通量.计算结果表明,经改写后的程序具有良好的加速效果.     

三维特征线的并行方法研究

设计了基于角度并行的三维特征线的并行算法。同时,为提高并行效率,采用了角度预分组和射线组合的策略,使通信量达到最小,并应用到中子输运方程的三维特征线计算程序TCM中。数值结果表明：角度并行方法和串行方法的结果完全一致,在采用了通信优化和负载平衡策略后,并行效率得到了显著提高。     

基于二维特征线方法的模块化六角形几何预处理方法

本文采用模块化特征线跟踪的方法,借鉴矩形几何的处理方式,针对六角形几何开发了几何预处理算法,得到的几何信息为特征线计算提供前端输入。实际编程发现该方法耗时在ms级别,效率很高。同时扩展了对六角形阵列和组件的几何描述,针对该几何预处理方法,研究了对应的边界条件描述方法,为特征线计算程序的编写奠定了基础。     

弥散颗粒型燃料特征线方法输运计算研究

弥散颗粒型燃料的中子输运问题因其特有的随机性和双重非均匀性难以直接使用现有输运方法进行求解。Sanchez-Pomraning方法借助更新方程,对特征线方法进行改进,使其能应用于弥散颗粒型燃料的输运计算中。本文对二维圆柱形弥散颗粒燃料输运问题进行了计算,数值结果表明：程序在不同颗粒填充率、不同颗粒尺寸、燃料颗粒与毒物颗粒共存的问题下均能保证较好的计算精度,反应性特征值绝对偏差大多低于100 pcm,仅在QUADRISO毒物颗粒填充时绝对偏差达到163 pcm。本文方法能满足弥散颗粒型燃料的输运求解要求,为新型燃料的设计研究工作提供了可靠的结果。     

三维球床几何稀疏条数长特征线加速方法

特征线法具有非常强的几何适应性,可用于三维球床高温气冷堆全堆芯求解,但存在迭代次数多、计算速度慢的缺点。本文将长特征线加速方法应用于三维球床高温气冷堆以解决非规则几何数值加速的问题,基于三维模型特征线布置较二维模型稠密的分析,提出了稀疏条数长特征线加速方法,极大地减少了加速方程的计算量,在不降低角度离散精度的前提下,获得了非常好的加速效果。通过基准题对加速参数的选取方式进行了研究,条数稀疏度取3～5、长特征线长度取2.0 cm左右、加速迭代步取20～60步可获得良好的加速效果。小型轻水堆三维基准题和球床堆芯简化模型的计算结果表明,采用稀疏条数长特征线加速可获得7倍左右的时间加速比,此时对应的迭代步加速比为20倍左右。     

Neutron Anisotropic Scattering Effect in Heterogeneous Cell Calculations of Light Water Reactors

A study on the anisotropic scattering effects in heterogeneous square cells of light water reactors has been performed using the characteristics method. It was found that the effects of the anisotropic scattering were relatively large for the MOX fuel cell because of the large neutron current from the moderator to the fuel region and the k _inf value by the P₀ calculation became 0.10–0.16% larger than that by the P₅ calculation. With the transport correction, the k _inf difference from the P₅ calculation became even larger than that from the P₀ calculation and the k _inf value by the transport correction became 0.18–0.25% larger than that by the P₅ calculation for the MOX fuel cell. The transport corrected self-scattering cross sections of the moderator region become smaller than the non-transport corrected ones and the angular flux distribution becomes more anisotropic with the transport correction. Therefore, more neutrons toward the moderator region between the fuel pellets can slow down to the lower energy region with the transport correction. As a result, the k _inf value by the transport correction becomes larger than that by the P₀ calculation, which is opposite effect to that by the P₅ calculation.     

Discrete Eigenvalues of Neutron Transport Equation with Quadratically Anisotropic Scattering

The general properties of discrete eigenvalues of the one-speed neutron transport equation with quadratically anisotropic scattering are studied analytically. We investigate the asymptotic behaviors of boundary curves of the complex discrete eigenvalues carefully and plot the distribution of the discrete eigenvalues in parameter space. Our predictions agree with numerical calculation     

Approximate Solution to Neutron Transport Equation with Linear Anisotropic Scattering

A method to obtain an approximate solution to the transport equation, when both sources and collisions show a linearly anisotropic behavior, is outlined and the possible implications for numerical calculations in applied neutronics as well as shielding evaluations are investigated.

The form of the differential system of equations taken by the method is quite handy and looks simpler and more manageable than any other today available technique. To go deeper into the efficiency of the method, some typical calculations concerning critical dimensions of multiplying systems are then performed and the results are compared with the ones coming from the classical S_N approximations. The outcome of such calculations leads us to think of interesting developments of the method which could be quite useful in alternative to other today widespread approximate procedures, for any geometry, but especially for curved ones.     

子群法与特征线法结合的中子共振计算

传统的中子共振自屏计算方法采用了有理近似,局限于处理简单的共振模型,在处理复杂燃料栅元/组件时会引入较大误差。为提高复杂情况下共振计算的精度,将子群法共振模型与特征线方法结合,推导了子群法-特征线法方程。基于WIMSD格式的69群数据库,编制了可用于任意二维几何中子共振计算的SGMOC程序。通过数值验证表明,该程序计算结果与MCNP程序计算结果吻合良好,具有较高的计算精度与几何通用性。     

宇宙线μ子散射成像技术研究进展

为进一步深入开展宇宙线μ子散射成像技术研究,发挥其在国土安全、防范核走私、核不扩散等方面的重要作用。论文综述了国内外在宇宙线μ子散射成像技术上的研究进展情况,提出了一些存在的问题以及未来的研究方向。     

Transport Calculations of MOX and UO2 Pin Cells by the Method of Characteristics

A new transport theory code for two-dimensional calculations of both square and hexagonal fuel lattices by the method of characteristics has been developed. The ray tracing procedure is based on the macroband method, which permits more accurate spatial integration in comparison to the equidistant method of tracing. The neutron source within each region is approximated by a linear function and linearly anisotropic scattering can be optionally accounted for. Efficient new techniques for both azimuthal and polar integration are presented. The spatial discretization problem in case of P ₁-scattering has been studied. Detailed analyses show that the P ¹-scattering in case of regular infinite array of fuel cells is significant, especially for MOX fuel, while the transport correction is inadequate in case of real geometry multi-group calculations. Finally, the complicated nature of the angular flux in MOX and UO₂ fuel cells is demonstrated.     

用质子弹散符合测量方法分析薄膜中氢分布的蒙特卡罗研究

本文从离子与物质相互作用的基本原理出发,用蒙特卡罗方法模拟了用质子弹性散射符合分析方法分析表面含氢的几组不同厚度的金属薄膜样品的实验,详细介绍了模拟过程中影响深度分辨率的多种因素,如束流能量、能损歧离、角度歧离等。本文基于2×1.7MV串列静电加速器可以提供的质子束能量范围,通过模拟计算得到用能量为1.5 Me V的质子束分析厚度为1~3微米的铝膜,深度分辨可以达到0.2微米。本文还给出了内部含氢的多层铝膜的模拟结果,表明此方法可以很好地分析薄膜内部氢元素的深度分布。     

基于OpenMP的中子输运方程特征线法并行计算研究

特征线法是目前求解反应堆中子输运方程的主要计算方法之一。本文开发了基于OpenMP的中子输运方程特征线法并行计算程序,以提高特征线法的计算效率。OpenMP是共享存储体系结构上的一个并行编程模型,采用Fork-Join并行执行方式,适合于SMP共享内存多处理系统和多核处理器体系结构。通过相关基准题测试验证,表明所开发的程序在有效增殖因数以及相对中子通量(归一化栅元功率)分布等参数上都能取得良好的精度,且使用OpenMP能取得良好的加速效果,使计算时间显著减少。     

Elastic Removal Self-Shielding Factors for Light and Medium Nuclides with Strong-Resonance Scattering

The self-shielding factors for elastic removal cross sections of light and medium weight nuclides were calculated for the parameter, σ_o within the conventional concept of the group constant sets. The numerical study were performed for obtaining a simple and accurate method. The present results were compared with the exact values and the conventional ones, and shown to be remarkably improved. It became apparent that the an-isotropy of the elastic scattering did not affect to the self-shielding factors though it did to the infinite dilution cross sections. With use of the present revised set, the neutron flux were calculated in an iron medium and in a prototype FBR and compared with those by the fine spectrum calculations and the conventional set. The present set showed the considerable improvement in the vicinity of the large resonance regions of sodium, iron and oxygen.