Preliminary analysis of the irradiation deformation of a typical molten salt reactor graphite component

Abstract

Nuclear graphite commonly serves as the moderator and constructs the coolant flowing channel in liquid fuel molten salt reactors. Under irradiation and high temperature, graphite components will experience obvious deformation due to irradiation creep, thermal expansion, dimensional change, elastic deformation, and thermo-mechanical properties change. The lifespan of graphite components is a limiting parameter of liquid fuel molten salt reactors, determining by the deformation of the graphite components. An improved approach based on the finite element method for graphite deformation analysis was proposed in this paper. Then this method was utilized to analyze a 10-year deformation history of a typical graphite component. The findings show that the stress-strain field of the graphite component significantly varies with the increasing irradiated neutron fluence. The dimensional change plays a primary role in influencing the deformation of the graphite components, determining the overall deformation trend. The irradiation creep plays a secondary role in influencing the deformation, alleviating the deformation of the graphite components to prolong the graphite lifespan. The improved method, which considers various factors like irradiation creep, thermal expansion, dimensional change, and elastic deformation, tends to provide more accurate results compared to the traditional method that focuses solely on the dimensional changes. Over 10 years, the contraction deformation of graphite components results in a reduction in graphite volume of up to 3.87%. The space for graphite contraction is filled with molten salt, resulting in a maximum increase of 22.49% in fuel volume. The alteration in volume of both graphite and fuel leads to a reduction in reactivity of up to 840 pcm.