A study of actinide decay chains on the environmental effect of a geologic disposal of `rock-like oxide' fuels and uranium–plutonium oxide fuels

Abstract

Currently, it is planned to dispose rock-like oxide fuel (ROX) spent fuels, like standard light water reactor (LWR) spent fuels and high-level radioactive wastes from reprocessing plants, in a repository located in a deep geologic formation. In order to demonstrate the usefulness of the ROX plutonium-burning system, a comparative study of environmental safety was carried out for the direct disposal of ROX and mixed-oxide fuel (MOX) spent fuels, both of which recycle plutonium. Analyses were performed for the case of ROX and MOX spent fuels disposed into a deep granite rock formation, and the individual dose equivalent, of actinide decay nuclides, due to the ingesting of contaminated drinking water was calculated based on a groundwater migration scenario. The amounts of disposed ROX and MOX spent fuels are equivalent to the generation of electricity by one metric ton of uranium metal (1 MTU). The committed dose equivalents from ROX spent fuels are less than those from MOX spent fuels by ca. 2 orders of magnitude in the conservative solubility case, and by at least one order of magnitude in the realistic solubility case. It is suggested that for actinide decay nuclides the ROX plutonium-burning system will be beneficial to repository safety. In order to confirm the behavior of geologic disposal of ROX spent fuels, it is recommended that the solubility of zirconia should be estimated by experimental studies.