Comparative Assessment of Thorium Fuel Cycle Radiotoxicity

Abstract

This paper compares the radiotoxicity of thorium-based and uranium-based spent nuclear fuels and reprocessing wastes to inform evaluation of whether thorium-based fuels are significantly less radiotoxic than uranium-based fuels, as has been claimed at times in the technical literature. A consistent approach for calculating the radiotoxicity is established for four oxide fuel types in a pressurized water reactor: low-enrichment uranium, uranium with plutonium fissile material, thorium with 233U fissile material, and thorium with plutonium fissile material. The results of the calculations are presented to display the radiotoxicity trends and are analyzed to determine (a) what underlies the indicated radiotoxicity trends for decay times from 1 year to 20 million years and (b) factors that may have led to erroneous conclusions concerning the comparative radiotoxicity of thorium- and uranium-based fuels. The overall conclusion is that the ingestion radiotoxicity of thorium-based fuels containing 233U or plutonium fissile materials is similar to the radiotoxicity of uranium-based fuels containing 235U or plutonium fissile materials but that within this overall similarity there are significant differences in radiotoxicity in specific eras during decay.