Abstract
A crucial step of nuclear fuel manufacture is the co-milling of uranium and plutonium oxides to obtain a targeted particle size and excellent mixing. However, the scale-up from the laboratory to plant production is still mainly empirical. The goal of this doctoral thesis is to model and characterize granular flows in rotating drums and to elucidate the mechanisms of particle grinding across scales. By means of particle dynamics simulations and a particle breaking model involving the tessellation of breakable particles into cells and a dynamic debonding criterion based on fracture mechanics, we investigate single- particle impacts, the properties of granular flows in the cascading regime in a rotating drum as a function of system parameters, the effect of the size and amount of grinding media on the grinding process, and the evolution of particle breakage in granular flows of breakable particles. Our simulations reveal several well- defined relationships between flow variables such as surface profile, flowing thickness, force fluctuations and wall slip, as well as with system parameters such as rotation speed, drum size and filling degree, and with particle fracture during flow. We identify a dimensionless parameter that can be used for the scale-up of rotating drums.