(核能力学专题)芯体多孔结构对单片式燃料元件辐照热-力耦合行为的影响研究

A UMo/Al monolithic fuel plate is composed of UMo fuel meat and Al cladding. These fuel plates with a high uranium density have a promising prospect to be used in advanced research and test reactors. Under the neutron irradiation environments, nuclear fissions occur to result in heat generation in the fuel meat; accumulation of fission-induced solid and gaseous products will lead to irradiation swelling; irradiation creep of UMo will affect the mechanical interactions between the fuel meat and the cladding. Especially, intragranular and intergranular gas bubbles will make the fuel meat evolve into a porous structure, and the fuel porosity and pore pressure will change continuously with the irradiation time. As a result, a complex irradiation-induced multi-scale thermo-mechanical coupling behavior needs to be simulated for optimal design and safety evaluation of UMo/Al monolithic fuel plates. In this study, a theoretical model for fuel porosity evolution is developed, based on a fission gas swelling model with the grain recrystallization, the resolution of intergranular gas atoms and the dependence of hydrostatic pressure involved. Moreover, the computation method of microscopic interfacial normal stress is established, with consideration of fuel porosity and pore pressure. The evolution model of fuel porosity is introduced into three-dimensional finite element simulation of the irradiation-induced multi-scale thermo-mechanical coupling behavior, which correlates the current thermal conductivity of UMo fuel with the fuel temperature and porosity. The distribution and evolution disciplines of thermo-mechanical variables in the fuel plate are obtained at different irradiation time. In addition, the effects of fuel porosity on the temperature, the main deformation and microscopic interfacial normal stresses are investigated. Simultaneously, the effects of surface heat transfer coefficient on the thermo-mechanical behavior are analyzed. The research results indicate that the porous fuel structure and fission-gas induced pore pressure become the main fracture mechanisms of monolithic fuel plates.