Calculation of Fuel Penetration and Freezing in Channels with a Two-Phase Flow Code

One of the more severe scenarios for a single subassembly accident in a liquid-metal fast breeder reactor is the formation of a bottled-up pool of fuel and steel in the assembly and its subsequent lateral discharge into a neighbor through a breach in the can wall. Most of the calculations and experiments to investigate this scenario have assumed that the discharge is single phase. Recent experimental evidence from SCARABEE suggests that the discharge is more likely to be two phase. A series of SIMMER calculations has been performed to examine the major features of a two-phase fuel discharge into a rod bundle. Flashing is found to reduce the mass flux of the discharge; the vapor so generated then accelerates the liquid in the discharge, resulting in higher melt velocities and generally deeper penetration of the discharge into the bundle before plugging occurs as compared with the singlephase case.