Uranium-233 Breeding and Neutron Multiplying Blankets for Fusion Reactors

A variety of blankets for fusion reactors were neutronically analyzed to determine the fusion energy multiplication factor (M), the heavy metal fission rate, the fissile atom production rate, and tritium production. The blankets studied were:

1. thorium metal, ThO₂, ThC₂, uranium metal, UO₂, UC, and UC₂ fast-fissioning blankets
2. nonfissioning thorium metal blankets
3. blankets that multiply neutrons in a ²³⁸U region and use those neutrons to breed tritium and ²³³U in a separate zone
4. beryllium, niobium, and molybdenum neutron-multiplying ²³³U breeding blankets.

The important conclusions are:

1. For maximum production of thermal energy throughout the fuel cycle per fusion neutron, plutonium breeding is preferable, with one exception: If high-conversion-ratio thermal fission reactors with recycle are used, uranium neutron-multiplying Th-²³³U breeding blankets hold a slight edge.
2. Metallic fuels offer a significant breeding gain over oxides or carbides. With a 1 MW/ m² neutron first-wall loading, typical burnups in the metals are 0.024 to 0.4%/yr, indicating that the metals are viable fuel concepts.
3. One substantially reduces the fissile breeding rate to obtain a nonfissioning configuration in thorium.
4. Thorium blankets of almost any type consistently fail to outperform plutonium breeding or uranium neutron-multiplying ²³³U breeding blankets on the basis of neutron utilization and total energy production.