A Comparison of the Environment, Health, And Safety Characteristics of Advanced Thorium-Uranium and Uranium-Plutonium Fuel Cycles
Ault, Timothy Mason
The environment, health, and safety properties of thorium-uranium-based (“thorium”) fuel cycles are estimated and compared to those of analogous uranium-plutonium-based (“uranium”) fuel cycle options using a structured assessment methodology. Thorium resource recovery as a measure of environmental sustainability is described in terms of resource availability, chemical processing requirements, and radiological impacts. Results indicate that near-term thorium recovery will occur as a by-product of mining for other commodities, particularly titanium, and could satisfy even the most intensive nuclear demand for thorium six times over. Chemical flowsheet and radiological process analyses show greater, but not insurmountable, impacts for thorium recovery compared to uranium recovery. Four fuel cycle options are compared: a modified-open uranium option, a modified-open thorium option, a closed uranium option, and a closed thorium option. The options are compared on the bases of resource sustainability, waste management (both low- and high-level waste), and occupational radiological impacts. At steady-state, occupational doses somewhat favor the closed thorium option while low-level waste slightly favors the closed uranium option, although uncertainties are significant. The high-level waste properties favor the closed options (especially with thorium), but uranium options produce slightly less I-129 and may present less risk in a repository environment. Resource requirements are much lower for the closed options and are relatively similar between thorium and uranium. In addition to the steady-state results, several potential transition pathways are considered for closed uranium and thorium end-states. For dose, low-level waste, and fission products contributing to repository risk, the differences among transition impacts largely reflect the steady-state differences. However, the high-level waste properties show the opposite result in transition (strongly favoring uranium, whereas thorium is strongly favored at steady-state), since used present-day uranium fuel is disposed in transitions to purely thorium-based options. Resource consumption was the only metric was strongly influenced by specific transition pathways, favoring the most rapid transitions regardless of whether thorium or uranium was used.