SUMMARY

The purpose of this research is to develop a methodology for a thorium fuel recycling analysis that provides results for an isotopics and radio-toxicity study. This research is motivated by the need to reduce the long term radiological hazard in spent nuclear fuel, which mitigates the mixing hazard 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 included the following pairs of comparison cases: low enriched uranium dioxide vs. thorium dioxide with 233-UOX, natural uranium dioxide mixed with transuranic oxides vs. thorium dioxide mixed with transuranic oxides , natural uranium dioxide mixed with weapons grade plutonium dioxide vs. thorium dioxide mixed with weapons grade plutonium dioxide, natural uranium dioxide mixed with reactor grade plutonium dioxide vs. and thorium mixed with reactor grade plutonium dioxide. 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.