Effect of swelling on thermal conductivity and postirradiation densification of U3Si

The effect of swelling porosity on the thermal conductivity of irradiated U 3 Si fuel was deduced from electrical conductivity measurements on samples with pore volume fractions of 0.01 to 0.27. The Maxwell‐Eucken expression adequately represents the data, with β= 1.9±0.1. Postirradiation annealing of samples at 400° to 750°C produces densification. Calculations confirm that the pores in as‐irradiated fuel are voids possibly containing a small amount of fission gas. Those retained after annealing are fission gas bubbles with internal pressure nearly in equilibrium with the surface tension of the surrounding solid.