Investigation on the Irradiation-thermal–mechanical coupling behaviors of the solid Microencapsulated fuel rod

Abstract

Solid Microencapsulated Fuel (SMF) is a kind of new accident-tolerant fuel (ATF), where the TRISO coated fuel particles are dispersed directly into a type of matrix in the form of a solid rod. SMF is expected to provide improved performance because of the elimination of cladding tube and associated failure mechanisms. This study aims to investigate the irradiation-thermal–mechanical coupling behavior of SMF rod under normal operation of the 200 MW Nuclear Heating Reactor (NHR200-II) using finite element method (FEM). Two kinds of SMFs have been evaluated and compared -with the fuel particles dispersed into a silicon carbide matrix or a zirconium matrix. The finite element models, considering comprehensive coupling behavior (including irradiation-induced dimensional change, irradiation-induced creep, thermal expansion, fission gas pressure, heat generation and conduction, elasticity and plasticity, etc.), were developed based on the ABAQUS platform and accurately verified. The study also investigated the impacts of key parameters on the coupling behavior of SMF, including particle kernel diameter, non-fuel zone width, extent of particle aggregation, and operational conditions. The results revealed that SMFs exhibit excellent heat transfer capability, resistance to deformation, and a stress-relaxed state under normal operation. Specifically, SMF-Zr exhibited a higher centerline temperature but lower levels of deformation and stress compared to SMF-SiC. The effects of fuel kernel diameter and non-fuel zone width were found to be limited, whereas higher particle aggregation and harsher operational conditions indeed increase temperature, deformation, and stress, particularly during the initial irradiation stage. Moreover, a higher creep coefficient of pyrolytic carbon leads to a more relaxed stress state. This study lays a fundamental basis for the design and optimization of this kind of solid particle-dispersed fuel.