Temperature fields in fresh and irradiated fuel (section V) Consider two conditions for heat transfer in the pellet and the pellet-clad gap of a BWR fuel pin. • Initial uncracked pellet with no relocation • Cracked and relocated fuel 1. For each combination, find the temperatures at the clad inner surface, the pellet outer surface, and the pellet centerline.
2. Find for each case the volume-weighted average temperature of the pellet. Geometry and material information Clad outside diameter = 12.52 mm Clad thickness = 0.86 mm Fuel-clad diametral gap = 230 pm Initial solid pellet with density = 88% Basis for heat transfer calculations Clad conductivity is constant at 17 W/m "K Gap conductance Without fuel relocation. 4300 W/m2K, With fuel relocation, 31,000 W/ m K ; Fuel conductivity (average) at 95% density Uncracked, 2.7 W/m K , Cracked, 2.4 W/m 'K; Volumetric heat deposition rate: uniform in the fuel and zero in the clad Do not adjust the pellet conductivity for restructuring. Use Biancharia's porosity correction factor (Eq. 8-21). Operating conditions Clad outside temperature = 295°C Linear heat-generation rate = 44 kW/m