ANALYSIS OF THE ANTINEUTRINO SIGNATURE OF LEU/MOX FUELED LWRS AND SFRS

One way to reduce the amount of weapons-grade plutonium is to convert it to mixed-oxide (MOX) fuel and then burn it in existing reactors. This process will require oversight and verification. One potential verification method was demonstrated by Anna Hayes (LANL) at the 2006 Applied Antineutrino Physics Workshop, in which the differences in antineutrino production over a burn-up cycle are used to differentiate between a low-enriched uranium (LEU) light water reactor (LWR) and a MOX LWR. This difference occurs because of the differences in evolving fissile isotopics between MOX and LEU assemblies. This work involves a more detailed analysis of antineutrino production for LWRs and an extension to sodium fast reactors (SFRs). For the LWR, different enrichment LEU and MOX assemblies are depleted to obtain time-dependent antineutrino production rates. These assemblies are then simulated at several burn-up steps and combined to obtain the antineutrino rate at the start of a fuel cycle in an equilibrium MOX core. This core uses LEU and weapons-grade MOX fuels to simulate an actual reactor that would dispose of weapons-grade plutonium. Parametric studies are performed with the equilibrium core to determine if diversion of weapons-grade MOX fuel assemblies is detectable using the antineutrino response. For the SFR, a characteristic reactor is modeled with ERANOS for weapons-grade MOX, reactor-grade MOX, and enriched UO2 to obtain the antineutrino rates as a function of burn-up. The results are then compared to the LWR. This work illustrates that while the evolution of antineutrino production during a single burn-up cycle does vary with enrichment, those differences are minor compared to the differences between LEU and MOX fuel. Furthermore, the ability to detect the removal of weapons-grade MOX assemblies from a core depends on whether it is replaced with LEU (more detectable) or reactor- grade MOX (less detectable). This shows that in certain cases, the diversion of weapons-grade MOX fuel may be detectable. The SFR analysis shows that antineutrino production remains relatively constant during a fuel cycle with some variation between enriched UO2 and MOX fuels. Antineutrino production from fertile isotopes is important due to the hard neutron spectrum of SFRs.