Graphite-filled MOX fuel design for fully loaded PWR cores

Abstract

The use of recycled plutonium plays an important role in saving natural uranium resources. During the past 40 years, many researches have been performed for the use of recycled plutonium. Currently, the reprocessed plutonium is used in a mixed-oxide (MOX) fuel form in light water reactors (LWRs). However, the MOX fuel loading is currently limited to 1/3 or half of the core. This partial loading results in heterogeneous cores where interface problems appear between uranium and plutonium assemblies due to the discrepancies between effective cross sections of the uranium and plutonium isotopes. The resulting need to zone the fuel enrichment inside the fuel assembly leads to ∼10% additional manufacturing costs. Consequently, there is a growing need for and interest in a full MOX core for better utilization of the recycled plutonium and for weapon’s plutonium disposition. In order to maximize the benefit of plutonium recycling in the current LWR cores, recently, a significant amount of researches has been performed for 100% MOX cores. However, when the LWR core is fully loaded with the MOX fuel, several problems arise due to the spectrum hardening effect of the plutonium isotopes. In order to overcome the spectrum hardening effect, a new fuel design for the full MOX core, which consists of annular fuel material filled internally with graphite (gMOX) or inert gas (aMOX), are proposed. The new design is compatible with the conventional fuel assembly in its overall geometry, and therefore it may require only minor modifications from the conventional fuel technologies. From the results of assembly analysis, it is ascertained that the void reactivities of the gMOX fuel assembly are more negative than those of a stMOX (standard MOX) fuel, while the aMOX fuel assembly has less negative void reactivities at a low burnup range. It is also shown that the maximum fuel rod temperature of the gMOX fuel is lower than that of stMOX fuel rod by ~ 130°K. This tendency is also obser...