Preliminary Insights on Potential Transitions to Closed Thorium-Based Fuel Cycles
Closed fuel cycles with comprehensive recycle strategies are often regarded as the logical and desired end-states of long-term nuclear energy strategies; such options offer potential improvements in terms of resource supply and sustainability, waste management, and potentially nuclear security. In the DOE-NE Fuel Cycle Option Campaign report, systems with closed recycle strategies (both uranium- and thorium-based) generally dominated strategies with less comprehensive recycle approaches across many performance metrics. That being said, developing momentum to transition from the current global implementation of once-through fuel cycles has proven challenging. Intermediate paths en route to closed fuel cycles have not been readily elucidated; this is especially true for thorium-based options. A comparatively extensive amount of work has been conducted on transitions to closed fuel cycles based on uranium and plutonium, generally based on an endpoint of sodium-cooled fast reactors (SFRs). In contrast, corresponding analyses for thorium-based options are limited. Early estimates, without the benefit of full-scale modeling, were performed in conjunction with the Molten Salt Fast Reactor (MSFR) design. There is some transition analysis work associated with the Japanese THORIMS-NES molten salt design, but the scope of this work was not directly comparable with the SFR-oriented analyses and considered the thorium fission reactors as an intermediate state en route to the global deployment of accelerator-driven systems. Others have considered thorium recently, but not in a closed-recycle context. To begin to resolve this gap, this paper describes a high-level analysis and initial perspectives on the topic of transitions to closed thorium-based cycles. The emphasis on this paper is not on the specific quantitative results that are described, although some of the overall takeaways from these trends may still be useful. Instead, this paper describes the need for such analyses to be conducted, describes the methodologies by which this can be accomplished, and reports an initial demonstration of these methodologies for a specific transition candidate scenario. (authors)