A Once-Through Fuel Cycle for Fast Reactors

A paradigm shift has altered the design targets for advanced nuclear energy systems that use a fast neutron spectrum. Whereas designers previously emphasized the ability of fast reactors to extend global reserves of fissile fuels, the overriding desire now is for reactor technologies that are “cleaner, more efficient, less waste-intensive, and more proliferation-resistant.” (Cheney, 2001, “U.S. National Energy Policy,” National Energy Policy Development Group, Washington, DC) This shift in priorities, along with recent design advances that enable high fuel burnup even when using fuels that have been minimally enriched, creates an opportunity to use fast reactors in an open nuclear fuel cycle. One promising route to this goal exploits a phenomenon known as a traveling wave, which can attain high burnups without reprocessing. A traveling-wave reactor (TWR) breeds and uses its own fuel in place as it operates. Recent design work has demonstrated that TWRs could be fueled almost entirely by depleted or natural uranium, thus reducing the need for initial enrichment. The calculations described here show that a gigawatt-scale electric TWR can achieve a burnup of 20%, which is four to five times that realized in current light water reactors. Burnups as high as 50% appear feasible. The factors that contribute to these high burnups and the implications for materials design are discussed.