Coupled Neutronic Thermal Fluid Dynamic Modelling of a Very High Temperature Reactor

Abstract

The Very High Temperature Reactor (VHTR) is designed to push the boundaries and capabilities of existing High Temperature Gas Reactor technology to higher levels, challenging the desired inherent and passive safety features. To ascertain the viability of the design requires a detailed understanding of the complex multiphysics within the reactor core and the associated energy removal system. Due to the scale of the calculation computational numerical models are utilised. During a transient the greatest challenge to inherent and passive safety design features will occur. To understand the core dynamics during these off normal conditions requires the use and development of coupled radiation transport thermal hydraulic codes. In this thesis the coupled radiation transport computational multiphase fluid dynamic FETCH model is applied to a generic block type VHTR. The purpose of this research is twofold. First to analyse the suitability of the FETCH model to be capable of capturing the physics inherent within the generic VHTR of interest. Secondly to analyse the suitability of the generic VHTR to operate within certain key safety constraints of interest. A necessary component of this research was to provide evidence to support the reliability and credibility of model solutions through the use of a continuous verification and validation automated framework. Also this PhD thesis includes the development and analysis of a Sub Grid Scale finite element methodology applied in the context of the multigroup neutron diffusion equations. The method was found to be superior to standard Continuous Galerkin finite element methods but suffered from stability issues associated with low, or zero, absorption coefficient terms.