Fragmentation of UO2 and UC drops entering a sodium pool

In this paper attention is focussed on whether coarse premixing of fuel and coolant is possible according to the jet penetration hypothesis, with applications to a hypothetical accident in a liquid metal cooled nuclear reactor. For UO2 or UC fuel drops entering a sodium pool, the rapid bubble growth and collapse phenomenon, followed by crust breakup due to jet penetration, is analyzed as a function of the system pressure and coolant temperature. It appears that the UO2-Na system fragments rapidly upon contact, for coolant temperatures above 3000C, while the corresponding temperature for the carbide fuel is around 6000C, at atmospheric pressures. For UO2 but not for UC, there is a cut off pressure in the 0.1 to 3 MPa range, above which the crust does not break up for a particular coolant temperatures between 400 and 8000C. Higher sodium temperatures aid the breakup for both fuels. One concludes that coarse premixing for UO2, but not necessarily for UC, is difficult to attain