基于EFEN-SP3方法的pin-by-pin中子动力学计算方法研究

为能直接给出安全分析所需的最热棒功率而不引入组件均匀化近似和精细功率重构近似,本文研究了基于栅元均匀化的pin-by-pin中子动力学计算方法。通过全隐式向后差分对多群时空中子动力学方程组的时间变量进行离散,采用指数函数展开节块-SP₃（EFEN-SP₃）方法求解含裂变介质的多群中子固定源方程组,通过高阶源展开技术消除了中子源分布与缓发中子先驱核分布形状不一致的问题。采用Ks因子、LW外推和粗网再平衡等加速技术提高计算效率。三维pin-by-pin中子动力学问题的数值结果表明：pin-by-pin中子动力学计算能直接给出单棒功率密度分布;高阶源展开技术可有效抑制计算偏差随时间步的累加效应;加速技术可将SP₃动力学计算的求解速度提高134.9倍。     

An improved three-dimensional wavelet-based method for solving the first-order Boltzmann transport equation

A new angular discretization scheme based on the Daubechies’ wavelets has been developed in recent studies. A decoupled S_N and wavelet expansion method was proposed. This paper discusses the limitations and improvements of this decoupled scheme. The scaling function, instead of the wavelet function, is applied as the basis function. It significantly improved the efficiency and computational stability. A new series of wavelets on the interval are applied instead of the ‘wrapped wavelets’, which eliminate the edge effect in the angular subdomain scheme. Based on the improvements, a wavelet-based neutron transport code package WAVTRAN is developed and the previous work is extended to the three-dimensional calculation and anisotropic scattering calculation. Numerical results demonstrate that the improvements are effective. Further investigations demonstrate that the wavelet-based angular discretization scheme is more powerful than the traditional ones in some highly anisotropic angular flux problems.     

提高引线键合机超声系统性能的若干因素的分析

概述了引线键合机超声系统的组成，分析了影响引线键合机超声系统的若干因素，在此基础上提出了一些优化超声系统性能的措施。     

电力参数交流同步采样截断误差的估计

对电力参数的理想情况（标准正弦量）采样数字化测量的典型算法（梯形法）的截断误差进行了分析，给出了误差与采样点数的关系；根据国家关于电能质量和公用电网谐波的标准规定，对非正弦状态下的误差也做出了符合实际的估计，在电网正常（允许畸变）情况下截断误差与采样点数的关系与理想波形时相同，这些结论可在采用交流采样技术的电力参数测量装置设计时进行误差分析提供参考。     

重复控制系统的设计方法

对于性能要求较高的伺服系统，采有重复控制，可以提高系统的鲁棒性。所设计的重复控制器，对于输入或干扰为阶跃，斜坡，正弦以及其它周期信号时，系统均能无稳态偏差跟踪或消除干扰，且具有良好的动态性能。     

Solution of the multiplying binary stochastic media based on L-P equation in 1D spherical geometry

In order to obtain the ensemble average k_eff for the binary stochastic media system, a statistical transport equation with eigenvalue is derived based on the L-P equation. Combined method of statistical and deterministic is proposed to deal with this problem. In the first step, Monte Carlo approach is employed to calculate the mean chord length of the background scattering material, deterministic transport method using diamond difference and source iteration is applied to solve the eigenvalue L-P equation. Test problems of different scattering ratios, different chord-path ratios and different number of random fissile lumps and simple UO₂-H₂O problem are calculated and compared with references. Results show that the eigenvalue L-P equation can provide the mean value of k_eff for the given stochastic systems in most cases.     

龙滩碾压混凝土芯样试件特性试验研究

介绍龙滩碾压混凝土现场芯样试件特性研究成果，内容包括碾压混凝土强度、弹性模量、超声波速度、动力特性和断裂特性等资料。论证了建造200m级龙滩碾压混凝土重力坝的可行性。     

数值反应堆的研究现状与发展建议

数值反应堆技术是基于多物理紧耦合的高精度、高分辨率、高置信度的高保真数值模拟技术,其目的是实现核反应堆内物理现象的精确数值呈现和分析,大幅度提高核反应堆的设计能力和安全运行能力,用数值技术驱动核能技术的快速发展。本文总结了国内外数值反应堆技术的研究现状,提出了数值反应堆技术的发展建议。     

六角形布置反应堆高保真物理计算方法研究与验证

俄罗斯商用压水堆VVER和大多数实验堆均采用了六角形紧凑型栅格布置,为了实现VVER和六角形实验堆的高保真数值模拟分析,本文基于数值反应堆物理计算程序（NECP-X）开展了六角形堆芯高保真计算方法研究和程序开发。首先,将全局-局部耦合共振自屏计算方法拓展至六角形堆芯,实现六角形堆芯燃料棒的全堆芯高精度共振计算;其次,基于2D/1D耦合输运计算方法研究了六角形堆芯的高保真计算方法;最后,为了提高全堆芯计算的计算效率,研究了基于区域分解松耦合的非结构网格的粗网有限差分（CMFD）加速方法,可以实现以矩形、六角形和其他多边形栅元为基础的pin-by-pin CMFD 加速。为了验证六角形堆芯高保真计算方法的精度和效率,计算了六角形C5G7基准问题,并分析了六角形输运计算方法的计算精度和CMFD方法的加速效果;将NECP-X程序应用于西安脉冲堆的2D全堆芯计算,与蒙特卡罗程序的结果对比表明NECP-X程序计算得到的特征值和功率分布均具有较高精度。因此,本文建立的六角形堆芯高保真计算方法可以应用于六角形堆芯的分析计算。      

Can Sub-Saharan Africa feed itself? The role of irrigation development in the region’s drylands for food security

ABSTRACT

This paper assesses the potential role of investments in irrigation in Sub-Saharan Africa in improving food security and self-sufficiency in the region. Focusing on the region’s drylands, the study identifies a potential for expanded irrigated area of 6–14 million hectares (ha), depending on technology costs and other factors. Linkage of these results with a global agricultural trade model shows that accelerated irrigation investment can effectively reduce growing food import dependency from 54% under a business-as-usual scenario to a much smaller 17–40%; and can also reduce the population at risk of hunger and child under-nutrition.