燃料棒边缘效应下的子群共振计算方法研究

共振伪核素子群方法可用于处理燃料棒内部空间相关的共振干涉效应,然而该方法只能计算径向均匀核子密度的燃料棒问题,无法处理因边缘效应造成的径向核子密度非均匀分布的问题。针对此问题,基于改进的伪核素理论,提出了一种新的伪核素方法。计算结果表明,该方法解决了原始共振伪核素子群方法无法处理的边缘效应问题,相比于Bondarenko迭代法和干涉因子法,具有更高的精度。     

提高子群法共振自屏计算精度研究

基于自行研制的子群法与特征线法相结合的中子共振自屏计算程序SGMOC,研究提高子群法计算精度的2种方法.数值验证表明,2种方法都能提高共振自屏计算精度.其中,采用随机干涉近似求解条件概率的共振干涉效应处理的修正效果约为(0.02％～0.23％)△k/k;考虑共振散射的修正效果约为0.1％△k/k;综合运用2种方法的修正效果约为(0.03％ ～0.27％)△k/k.     

基于子群方法的双重非均匀性共振计算方法研究

为计算双重非均匀性条件下的共振截面,提出了耦合Sanchez-Pomraning方法的改进的子群方法(ISSP)。ISSP采用精细化共振能群结构来规避共振干涉处理,通过求解双重非均匀性条件下的子群固定源方程和慢化方程得到颗粒和基体等各材料的有效共振截面,最后进行双重非均匀性条件下的输运计算。数值结果表明,与连续能量蒙特卡罗程序及超细群计算结果相比,ISSP可精确高效地计算双重非均匀性条件下的共振截面。     

复杂燃料成分的多核素共振干涉计算方法研究

共振干涉现象广泛存在于反应堆系统中,是影响共振计算精度的重要因素之一。当前提出的干涉因子方法,其计算效率难以适用于燃耗过程中的复杂燃料成分。基于改进的伪核素理论与超细群慢化方程求解程序,提出了一种针对实际压水堆燃耗过程的快速共振干涉计算方法。对于燃耗过程中的复杂燃料成分,在均匀问题和压水堆栅元几何下进行了共振自屏分析。结果表明,该方法的计算精度与严格的超细群计算及蒙特卡罗方法相当,效率上优于干涉因子方法,适用于压水堆燃耗过程中的快速共振计算。     

基于子群共振自屏方法的特征值隐式敏感性分析

采用经典微扰理论,高效地得到问题相关的多群截面的扰动对特征值的直接影响,即显式敏感性。应用广义微扰理论,推导了在子群共振自屏方法中,多群共振自屏截面对非共振核素截面的灵敏度系数的计算方法。结合前两项内容,得到非共振核素通过共振自屏过程对特征值的间接影响,即隐式敏感性。根据与显式灵敏度系数的比较,分析了隐式敏感性相对于显式敏感性的重要性。     

传统共振计算方法改进措施的初步可行性研究

基于等价理论通过预制的共振积分表来插值产生具体问题共振能区有效截面的方法是反应堆物理计算中传统的共振处理方法,有着十分广泛的应用。为弥补传统方法在处理空间效应和多核共振干涉效应方面尚存在的不足,本文以SCALE软件包中的CENTRM和NITAWL共振处理模块为工具,研究探讨了一种简便易行的改进措施,有望在今后的堆芯计算中得到应用。     

基于子群方法的快谱共振计算方法研究

为了应对特征线精细几何计算对传统快谱共振计算方法带来的挑战,基于具有良好的几何适应性和计算精度的子群方法,对快谱共振截面计算进行了研究。采用伪共振核素法处理多核素间的共振干涉效应,具有较高精度的同时,能够避免Bondarenko迭代方法计算耗时的缺点。结合粒子群算法对子群参数进行求解,得到的子群参数具有较高的拟合精度。最后基于特征线方法对中国实验快堆（CEFR）和美国裂变星表电源系统（FSP）的单栅元问题进行了验证。计算结果表明,对于验证的快谱栅元问题,截面最大相对偏差分别为2%、3%,特征值绝对偏差分别为54 pcm、146 pcm。本文方法可以有效处理快谱中的共振截面计算问题。     

复杂几何燃料组件的共振自屏计算

共振参数计算是反应堆堆芯设计计算中的重要内容,传统的共振计算模型只适应于简单几何计算。本工作应用A.Hebert提出的子群共振自屏计算模型研制了复杂几何燃料组件的共振自屏计算程序。该程序能处理含有两种共振核素的复杂几何下的共振自屏。对一系列问题的数值校验计算表明,该模型在低富集度时具有较好的计算精度。     

NECP软件包中NECL子群数据与任意几何共振模块研制

本文基于子群方法对NECP软件包开发了多群数据库模块和子群共振计算模块。采用本实验室开发的二维任意几何输运程序矩阵MOC作为子群共振模块的求解器。使用MCNP与子群程序计算一系列的共振基准题,并比较了两者所计算的无限增殖因数k_inf和²³⁵U与²³⁸U的微观截面。结果表明,子群程序对任意几何有良好的适应性和精度,可适用于二维任意几何的共振计算。     

聚变驱动次临界堆双冷嬗变包层多群中子截面数据库共振自屏效应计算与分析

依据聚变驱动次临界反应堆 (FDS I)系统设计方案 ,使用Njoy和Transx程序 ,制作了 2 5群、1 75群、62 0群忽略和考虑共振自屏效应的中子截面核数据库 ,用Anisn程序计算了系统的有效增殖系数和各种反应率。结果表明 ,共振自屏效应对FDS I系统的各种反应率有很大的影响。     

Spatially Dependent Self-Shielding Method with Temperature Distribution for the Two-Dimensional Transport Code PARAGON

The Spatially Dependent Dancoff Method (SDDM) was recently developed to evaluate the power distribution within a fuel rod that has spatial variation of isotopic contents. The method was validated and verified by comparison to Monte Carlo calculations and measurements. However, those evaluations and comparisons were based on the assumption that the temperature distribution within a rod is flat. In this study, an equation used in the SDDM is enhanced in order to more accurately treat the temperature distribution. The enhancement was carried out with the knowledge that a Monte Carlo calculation shows no effect of temperature distribution on spatial flux within a rod. This leads to the cancellation of reaction rate changes due to temperature distribution between inner and outer regions within a rod. The knowledge gained from these evaluations was then applied to the equation used in the SDDM with the temperature distribution. The improved SDDM was validated and verified by comparison to MCNP4C calculations. PARAGON with the improved SDDM is now capable of performing micro-nuclear physics calculations with greater accuracy.     

Resonance self-shielding method using resonance interference factor library for practical lattice physics computations of LWRs

This paper presents a new method of resonance interference effect treatment using resonance interference factor for high fidelity analysis of light water reactors (LWRs). Although there have been significant improvements in the lattice physics calculations over the several decades, there exist still relatively large errors in the resonance interference treatment, in the order of ～300 pcm in the reactivity prediction of LWRs. In the newly developed method, the impact of resonance interference to the multi-group cross-sections has been quantified and tabulated in a library which can be used in lattice physics calculation as adjustment factors of multi-group cross-sections. The verification of the new method has been performed with Mosteller benchmark, UO₂ and MOX pin-cell depletion problems, and a 17×17 fuel assembly loaded with gadolinia burnable poison, and significant improvements were demonstrated in the accuracy of reactivity and pin power predictions, with reactivity errors down to the order of ～100 pcm.     

The pseudo-resonant-nuclide subgroup method based global–local self-shielding calculation scheme

The pseudo-resonant-nuclide subgroup method (PRNSM) based global–local self-shielding calculation scheme is proposed to simultaneously resolve the local self-shielding effects (including spatial self-shielding effect and the resonance interference effect) for large-scale problems in reactor physics calculations. This method splits self-shielding calculation into global calculations and local calculations. The global calculations obtain the Dancoff correction factor for each pin cell by neutron current method. Then an equivalent one-dimensional (1D) cylindrical problem for each pin cell is isolated from the lattice system by preserving Dancoff correction factor. The local calculation is to perform self-shielding calculations of the equivalent 1D cylindrical problem by the PRNSM. The numerical results show that PRNSM obtains accurate spatial dependent self-shielded cross sections and improves the accuracy of dealing with the resonance interference over the conventional Bondarenko iteration method and the resonance interference factor method. Furthermore, because both global and local calculation is linearly proportional to the size of problems, the global–local calculation scheme could be applied to large-scale problems.     

Resonance Self-Shielding Corrections for Activation Cross Section Measurements

The Pade approximations of the Doppler broadening function ψ(θ, x) have been used for the calculations of resonance self-shielding factors used in activation measurements. It is shown that this method of the calculations is effective from the point of view of fastness and accuracy.