The fission power of a conceptual fluidised bed thermal nuclear reactor

Abstract

The fluidised bed thermal nuclear reactor investigated in this paper is an innovative reactor design in which I mm diameter TRISO-coated fuel particles are fluidised by helium gas coolant in a 2.5 m diameter and 6 m high cylindrical bed. The coolant flow rate provides part of the reactivity control mechanism. The TRISO-coated particles have an enriched uranium oxide kernel surrounded by layers of porous carbon, pyrolytic carbon and silicon carbide. This paper presents detailed transient modelling results of this conceptual fluidised bed thermal nuclear reactor obtained using the FETCH nuclear criticality model. Previous work has provided evidence to suggest that such a reactor can be dynamically stable for low power outputs of ∼20 MWt. This work focuses on a reactor with a much higher thermal output of 100 MWt. To simulate the fluidised bed reactor the FETCH model has been used to solve the neutron transport equation in full-phase space, coupled to multi-phase gas-particle fluid dynamics. The main difficulty in modelling such a reactor is that its reactivity is a sensitive function of the fuel particle distribution inside the inner fluidised bed reactor cavity. This fuel particle distribution varies chaotically with time which is the root cause of the reactor's power variability.