Safety and neutronics: A comparison of MOX vs UO2 fuel

One of the issues associated with nuclear energy involves determining what should be done with spent nuclear fuel. In other countries, plutonium is recovered from spent fuel and is burned in reactors. Plutonium is not used currently as a fuel in the United States (US); however, as part of international negotiations, weapons-grade plutonium may soon be burned in US light-water reactors as mixed oxide (MOX) fuel. Both neutronic and safety parameters for MOX fuel vary from traditional uranium oxide (UO2) fuel, so it is important to be aware of these variances. Differences between weapons-grade plutonium and plutonium from spent nuclear fuel (reactor-grade plutonium) also exist because reactor-grade plutonium contains more 240Pu and higher actinides. To burn a significant portion of plutonium from spent nuclear fuel using full cores of MOX fuel would be advantageous; however, only one-third cores are being used today worldwide and are proposed for the Materials Disposition program in the US. This paper addresses the neutronic and safety differences between UO2 and MOX fuel (with both weapons- and reactor-grade plutonium) and between one-third and full cores of MOX fuel.