“Densification and thermal properties of cylindrical graphite-based fuel elements used in a molten salt reactor”

Based on the service characteristics of fuel elements for molten salt reactors, the design and preparation of fuel elements with high power density, densification resistance to coolant infiltration, and excellent thermodynamic properties are the focus of research. In this paper, for the problem that the base graphite of fuel element for molten salt reactor is not resistant to molten salt infiltration, carbon black (CB) is added to densification modification of the graphite A3-3, and the graphite substrate and fuel element are prepared by cold isostatic pressing process. The out-of-heap performance study shows that the densification and pore structure of the modified graphite matrix ATH-15 are optimized, and the resistance to molten salt infiltration is improved. The median pore size of the densification-modified graphite was reduced from 673 nm to 433 nm and the threshold pressure for molten salt FLiBe was increased from 0.88 MPa to 1.37 MPa. Isotropic CB improved the anisotropic properties of the graphite substrate, while its thermal conductivity and compressive strength were reduced due to the difficult graphitization of CB. Fuel elements with a filling fraction of 20%vol can be prepared using the modified graphite matrix ATH-15. Numerical simulations show that the power and temperature of the fuel elements match with this loading is optimal, and the fuel elements before and after modification have the same heat transfer behavior. In conclusion, the modified graphite matrix has significantly improved in terms of densification, pore structure, anisotropy and resistance to resistance salt infiltration, which meets the performance requirements of graphite-based fuel elements for molten salt reactors.