Improved Estimation of Anisotropic Neutron Diffusion Coefficients for Neutron Streaming in Advanced Gas Cooled Reactors (AGRs): Application to Steam I

先进气冷堆 (AGR) 中中子流的各向异性中子扩散系数的改进估计：在蒸汽中的应用 I

• 批准号: 2168598
• 金额: --
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2168598
• 关键词: Improved; Estimation; Anisotropic; Neutron; Diffusion

The aim of this PhD project is to address numerical modelling challenges within Advanced Gas Cooled Reactor (AGR) Nuclear Power Plants (NPPs). In reactor physics analyses of AGRs one needs to determine power distribution within AGR fuel assemblies (stringers). In order to determine these power distributions one must solve the neutron diffusion or neutron transport equation. If one solves the neutron diffusion equation (an approximate form of the neutron transport equation) radial and axial neutron diffusion coefficients along with other nuclear cross-section data must be calculated and used as input data within the codes. These radial and axial homogenized neutron diffusion coefficients must be corrected to take into consideration the detailed effects of neutron streaming in AGR gas channels. The correction factors for these radial and axial neutron diffusion coefficients can be very significant for the AGR geometry; in the region of around 10-30%, and results in differing directional diffusion coefficients in the radial and axial directions being used in the whole core reactor analysis simulations. For AGR normal operation, these correction factors are fairly constant and produce diffusion parameters which agree well with measurements, e.g. of distorted radial/axial flux shapes. A current concern for AGRs is the reactivity effects of steam ingress into an operating or shutdown AGR core. As graphite weight loss increases, the reactivity effects of the hydrogen addition can change from net negative to net positive. In addition, the hydrogen fills the streaming voids in the cluster, resulting in a loss of neutron streaming, reduction in leakage and further reactivity addition. The latter effect is only partially represented in lattice physics calculations, and therefore a generous uncertainty is currently used to provide numerical bounds to this effect. The aim of this PhD project will be to determine new mathematical/computational methods for calculating the assembly homogenized radial and axial neutron diffusion coefficients. These new mathematical/computational methods will aim to reduce the pessimism in AGR reactor physics simulations, as compared against reference neutron transport theory simulations, in order to ascertain the accuracy of the newly developed methods. In addition these methods can be re-applied to generation IV nuclear power plants (NPPs) such as high temperature gas cooled reactors (HTGCRs) and gas cooled fast reactors (GCFRs).

这个博士项目的目的是解决先进气冷堆（AGR）核电站（NPP）内的数值模拟挑战。在AGR的反应堆物理分析中，需要确定AGR燃料组件（纵梁）内的功率分布。为了确定这些功率分布，必须求解中子扩散或中子输运方程。如果求解中子扩散方程（中子输运方程的近似形式），则必须计算径向和轴向中子扩散系数沿着以及其他核截面数据，并将其用作代码中的输入数据。这些径向和轴向均匀化的中子扩散系数必须进行校正，以考虑中子流在AGR气体通道中的详细影响。这些径向和轴向中子扩散系数的校正因子对于AGR几何形状可能非常重要;在大约10- 30%的区域中，并且导致在整个堆芯反应堆分析模拟中使用的径向和轴向方向上的不同定向扩散系数。对于AGR正常操作，这些校正因子是相当恒定的，并且产生与测量（例如，扭曲的径向/轴向通量形状）很好地一致的扩散参数。AGR目前的一个问题是蒸汽进入运行或停堆AGR堆芯的反应性影响。随着石墨重量损失增加，氢添加的反应性效应可以从净负变为净正。此外，氢填充了团簇中的流动空隙，导致中子流的损失，泄漏减少和进一步的反应性增加。后一种效应在晶格物理计算中仅部分表示，因此目前使用慷慨的不确定性来提供这种效应的数值界限。这个博士项目的目的将是确定新的数学/计算方法，用于计算组件均匀化的径向和轴向中子扩散系数。这些新的数学/计算方法旨在减少AGR反应堆物理模拟中的悲观情绪，与参考中子输运理论模拟相比，以确定新开发的方法的准确性。此外，这些方法可以重新应用于第四代核电厂（NPP），如高温气冷堆（HTGCR）和气冷快堆（GCFR）。