Simulated Heat Transfer out of a Metallic Cruciform CANDU Fuel Element

Preliminary FlexPDE simulations were run to quantify the temperature distribution and surface heat flux conditions in a theoretical Uranium-Zirconium alloy, helical, cruciform shaped fuel element. A thermohydraulic model of the CANDU-6 pressure tube was created and used to predict a single phase convection heat transfer coefficient of 6.59 W/cm2K for a metal fuel element bundle, a 32% enchantment compared to conventional fuel bundle. At the conventional CANDU fuel pellet centerline melting power level of 70 kW/m, the metal alloy fuel had a simulated peak temperature of 610C, which is 1115C below its solidus melting temperature. The heat flow inside the fuel element was not radially symmetrical, and the surface normal to the short axis of the cruciform had the highest heat flux. The simulation indicates the high heat flux regions would produce sustained subcooled nucleate boiling at linear power levels above 40 kW/m.