An assessment of safety margins for stable swelling of U-Mo alloy fuel

A new model for the behavior of U-Mo fuel in the high temperature gamma phase is used in conjunction with an existing model for gas-bubble behavior in the irradiation-stabilized gamma regime in order to assess the temperature dependence of fission gas swelling. The swelling at high temperature is primarily intragranular, whereas at low temperature intergranular swelling becomes appreciable. A multi-atom gas-bubble nucleation mechanism in uranium alloy nuclear fuel operating in the high-temperature equilibrium gamma phase is proposed based on interpretation of measured bubble-size distribution data. The multi-atom nucleation mechanism is also operative at low temperatures, but primarily affects bubble nucleation on the grain boundaries. The capability to calculate swelling behavior in U-Mo fuel across the entire temperature spectrum enables an assessment of safety margins for stable swelling of U-Mo alloy fuel. (author)