Neutronic analyses of americium burning U-free inert matrix fuels

Abstract

Burnup characteristics of americium burning U-free inert matrix PuO2+ZrO2 (ROX), and PuO2+ThO2 (TOX) with reactor- and weapons-grade plutonium fueled LWR cell are analyzed in comparison with a conventional UO2 and MOX fueled LWR cells. In these fuels, 212–1062 kg/GWe of AmO2 are added to optimize an adequate amount for an effective burning of Am and Pu as well. It is found that a small amount of AmO2 act as a burnable poison in UO2 fuel to decrease the excess reactivity at BOL. Thermal neutron spectrum of ROX + AmO2 fuel is softer than the other fuels due to the lack of secondary source of fissile material, which accelerate the fission reaction rates of 242MAm, 242GAm, 243Am and capture reaction rates of 241Am, 243Am. As a result, the effective burning of Am and Pu isotopes especially 241Am and 239Pu are great in amount in ROX + AmO2 fuel even though the production of 242Cm, 244Cm, 238Pu from Am are nearly same in these fuels. In ROX + AmO2 fuel, the production of long-lived fission products (LLFPs) and 237Np are little. By analyzing the quality of spent fuels and safety characteristics, 650–750 kg/GWe of Am are proposed for ROX fuel for once through burning.