Analysis of multi-recycle thorium fuel cycles in comparison with once-through fuel cycles

The purpose of this research is to develop a methodology for a thorium fuel recycling analysis that provides results for isotopics and radio-toxicity evaluation and analysis. This research is motivated by the need to reduce the long term radiological hazard in spent nuclear fuel, which mitigates the mixing hazard (radiotoxicity and chemical toxicity) and decay heat load on the repository. The first part of the thesis presents comparison of several once-through cases with uranium and thorium fuels to show how transuranics build up as fuel is depleted. The once-through analysis is performed for the following pairs of comparison cases: low enriched uranium dioxide (UOX) vs. thorium dioxide with 233UOX (233U-ThOX), natural uranium dioxide mixed with transuranic oxides (U-TRUOX) vs. thorium dioxide mixed with transuranic oxides (Th-TRUOX), natural uranium dioxide mixed with weapons grade plutonium dioxide (U-WGPuOX) vs. thorium dioxide mixed with weapons grade plutonium dioxide (Th-WGPuOX), natural uranium dioxide mixed with reactor grade plutonium dioxide (U-RGPuOX) vs. thorium mixed with reactor grade plutonium dioxide (Th-RGPuOX). The second part of the research evaluates the thorium fuel equilibrium cycle in a pressurized water reactor (PWR) and compares several recycling cases with different partitioning schemes. Radio-toxicity results of the once-through cycle and multi-recycle calculations demonstrate advantages for thorium fuel and reprocessing with respect to long term nuclear waste management.M