Impact of reprocessed uranium management on the homogeneous recycling of transuranics in PWRs

This paper presents the results of a neutronics analysis related to the homogeneous recycling of different mixtures of transuranic elements (transuranics) (TRU) in pressurized water reactors (PWRs) loaded with mixed oxide (MOX) fuel using enriched uranium instead of depleted uranium (U_enrO₂-TRUO₂, i.e., MOX-EU). It also addresses an often, if not always, overlooked aspect related to the recycling of TRU in PWRs, namely, the use of reprocessed uranium. From a neutronics point of view, it is possible to multirecycle the entirety of the plutonium with or without neptunium and americium in a PWR fleet using MOX-EU fuel in between one-third and two-thirds of the fleet. Recycling neptunium and americium with plutonium significantly decreases the decay heat of the waste stream between 100 to 1000 years compared to that of an open fuel cycle or when only plutonium is recycled. The uranium present in MOX-EU used fuel still contains a significant amount of ²³⁵U, and recycling it makes a major difference in the natural uranium needs. For example, at equilibrium, a PWR fleet recycling its plutonium, neptunium, and americium in MOX-EU needs 28% more natural uranium than a reference UO₂ open cycle fleet generating the same energy if the reprocessed uranium is not recycled and 19% less if the reprocessed uranium is recycled back in the reactors, i.e., a 47% difference. Reenriching the reprocessed uranium is not necessary.