Analysis of metal fuel/cladding metallurgical interaction during off-normal transient events with phase diagram of the U-Pu-Zr-Fe system

To assist in understanding metal fuel performance at elevated temperatures, phase diagrams of the U-Pu-Zr, U-Pu-Fe, U-Zr-Fe and U-Pu-Zr-Fe systems at 800 °C were calculated based on thermodynamic data that has been previously evaluated. The calculated phase diagrams were compared with phase composition data at the interdiffusion zones, which formed at the interface between the irradiated or unirradiated U-Pu-Zr metal fuel and stainless steel cladding at temperatures of 800 °C or higher in literature. Each phase formed at the interface was successfully identified. It was confirmed that even in transient tests of the irradiated fuel pins, these phase diagrams are applicable to analysis of the multi-component interdiffusion zones between the metal fuel and the iron-based cladding.