Modelling and Simulation of Transient Nuclear Criticality Excursions Containing Special Nuclear Materials

这个由Sellafield Ltd和NDA赞助的PHD项目的目的是开发新的数学和计算方法，用于模拟含有特殊核材料(SNM)的松散耦合系统相互作用的阵列的核临界漂移行为[1，2，3，4]，其中一些阵列组件是亚临界的，一些是超临界的，或者在系统中引入了外部(或外部)中子源。在这项拟议的研究中，为“确定”多点核反应堆动力学方程中的耦合系数所采取的方法将是使用几何一致性方法，该方法将准确地模拟各个子系统(例如圆柱体、盒子或其他此类容器)的几何形状。这种几何一致性方法将使用基于伴随的加权来计算离开一个子系统和进入另一个子系统的中子的重要性。这具有一个重要的优点，即还可以使用单一方法来确定多点核反应堆动力学方程中所需的核反应堆动力学参数(例如，平均产生时间、β有效、基模伴随加权源项和伴随加权前体浓度)[39]。对于每个不同的子系统，将根据松散耦合系统的各个子系统组件的物理特性，推导出一组热工-水力方程。例如，如果它是一个粉末系统，那么湿粉末的物理和热水力将是合适的(类似于乳剂、胶体、悬浮液、金属系统、污泥、蛋糕和浆液)。

The aim of this Sellafield Ltd and NDA sponsored PhD project is to develop novel mathematical and computational methods for modelling the nuclear criticality excursion behaviour of interacting arrays of loosely coupled systems containing special nuclear material (SNM) [1, 2, 3, 4] where some of the array components are sub-critical and some are super-critical or where an extraneous (or external) neutron source is introduced into the system. The approach taken in this proposed research to "determine" the coupling coefficients in the multi-point nuclear reactor kinetics equations will be to use a geometry conforming approach that will exactly model the geometry of the individual sub-systems (e.g., cylinders, boxes or other such vessels). This geometry conforming approach will use adjoint based weighting to also calculate the importance of neutrons leaving one sub-systems and entering another sub-system. This has the important advantage that a single methodology can also be used to determine the nuclear reactor kinetics parameters needed in the multi-point nuclear reactor kinetics equations (e.g., mean generation time, beta-effective, fundamental mode adjoint weighted source terms and, adjoint weighted precursor concentrations) [39]. For each of the different sub-systems a set of thermal-hydraulic equations will be derived depending upon the physics of the individual sub-system component of the loosely coupled system. For example, if it were a powder system then the physics and thermal hydraulics of wetted powders would be appropriate (similar with emulsions, colloids, suspensions, metallic systems, sludges, cakes, and slurries).