Measurement of fission gas release from irradiated UMo dispersion fuel samples

• Three distinct fission gas release events were observed for irradiated UMo dispersion fuel.
• The first event is associated with release from fission gas recoiling into the matrix.
• The second event is associated with release of intergranular fission gas bubbles.
• The third event is associated with an exothermic reaction between the fuel and surrounding matrix.
• High temperature release is associated with the intragranular fission gas nanobubble superlattice.

The uranium-molybdenum (UMo) alloy dispersed in an AlSi matrix has been proposed as one fuel design capable of converting some of the world’s highest power research reactors from the use of high enriched uranium (HEU) to low enriched uranium (LEU). One aspect of the fuel development and qualification process is to demonstrate appropriate understanding of the extent of fission product release from the fuel under anticipated service environments. In this paper, two irradiated samples containing 53.9 vol% U-7wt% Mo fuel particles dispersed in an Al-2wt% Si matrix were subjected to specified thermal profiles under a controlled atmosphere using a thermogravimetric/differential thermal analyzer coupled with a mass spectrometer inside a hot cell. Measurements revealed three distinct fission gas release events for the samples from 400 to 700 °C, as well as a number of minor fission gas releases below and above this temperature range. The mechanisms responsible for these events are discussed, and the results have been compared with available information in the literature with exceptional agreement.