Direct self-recycle thorium fuel cycle in the advanced CANDU reactor

This report presents reactor-physics results of calculations for a possible thorium fuel cycle in the Advanced CANDU Reactor (ACR). Note however that this cycle can, as well, be applied to the CANDU-6 reactor line. The calculations presented here were performed with the lattice code WIMS-AECL. Since thorium is not a fissile, but rather a fertile, nuclide, another fissile nuclide must be used in a thorium fuel cycle, as a source of neutrons to drive the thorium. The fuel cycle proposed here is called the Direct Self-Recycle Thorium Cycle. In this approach, thorium and slightly enriched uranium (SEU) are used together throughout the fuel cycle. This is accomplished by loading both fuels, ThO2 and UO2, in different pins of a 'mixed bundle'. The bundle proposed for this use is the 43-element CANFLEX bundle, which is the preferred fuel carrier for advanced CANDU fuel cycles. This 'direct self-recycle' option is therefore an extension of the once-through cycle, with recycling which does not involve reprocessing. Since the fuel pellets are not removed from the elements, and the latter are not altered in any way, and, since, further, no chemical reprocessing is involved, the direct self-recycle option would have a high degree of proliferation resistance. In addition, it has the potential of being substantially less expensive than reprocessing technology. While not optimized, the direct self-recycle thorium fuel cycle described here would provide very competitive values of uranium utilization (7.37 MWd/kg[NU]) and spent-fuel generation (0.099 kg[IHE]/MWd[e]). Optimizing some of the fuel cycle parameters, such as the relative quantities of thorium and uranium and the enrichment of the uranium, may possibly lead to further improved results. This cycle will also allow the build-up of a mine of valuable U-233, which could be recovered in the future, once proliferation-resistant technologies are developed