5.15 - U-Si Based Fuel System

From the 1970s, the US started the Reduced Enrichment for Research and Test Reactors (RERTR) program, which is still active today. With regards to research reactors, the main objective of the program was, and still is, to convert the fuel from HEU to a Low-Enriched Uranium (LEU) based variant. Typically for the high power research reactors an enrichment of 19.75 ± 0.25% is chosen. The simple replacement of the HEU content of research reactor fuels by LEU would result in a decrease of the fissile material density by a factor of ~5, which is not compatible with the design of the research reactors. Starting from the U-Al fuel system, increasing the volume of UAlx in the fuel plates has its limits. Of the other, higher density uranium compounds, alloys and intermetallics, the most favourable candidate is U3Si2 (low temperature application) or U3Si (high temperature application). In this article, the different aspects of the research reactor fuel cycle for the U-Si based dispersion fuel systems are introduced. From the basic properties of the material through the manufacturing process, proceeding to the in-pile fuel behavior and eventually the processing of the spent fuel.