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

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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).