Improving performance with accident tolerant-fuels

Abstract

After the Fukushima reactor accident, efforts to improve risk management in nuclear operations have included the intensification of research on accident-tolerant fuels (ATFs). In this investigation, the physical properties of recently developed ATFs were compared with those of the current standard fuel, UO2–Zr. The goals for innovative fuel design include a rigorous characterization of the thermal, mechanical, and chemical considerations. The intentions are to lengthen the burnup cycle, raise the power density, and improve safety. Fuels must have a high uranium density—above that supported by UO2—and possess a coating that exhibits better oxidation resistance than Zircaloys. ATFs such as U3Si2, UN, and UC contain a higher uranium density and thermal conductivity than UO2, providing significant benefits. The ideal combination of fuel and cladding must increase performance in a loss-of-coolant accident. However, U3Si2, UN, and UC have a disadvantage; their respective swelling rates are higher than that of UO2. These ATFs also have thermal conductivities approximately four times higher than that of UO2. A study was conducted investigating the hydrogen generated by the oxidation of zirconium alloys in contact with steam using cladding options such as Fe-Cr-Al and silicon carbide. It was confirmed that ferritic alloys offer a better response under severe conditions, because of their mechanical properties as creep rate. The findings of this study indicate that advanced fuels should replace UO2–Zr as the fuel system of choice.