A paradigm shift has recently altered the design targets for advanced nuclear energy systems that use a fast neutron spectrum. A previous emphasis on extending fissile fuel reserves has been supplanted by a desire for reactor technologies that are “cleaner, more efficient, less waste-intensive, and more proliferation-resistant.” [1] This shift, along with recent advances in fast-reactor designs that enable high fuel burn-up even with fuels that have been minimally enriched, creates an opportunity to employ fast reactors in an open nuclear fuel cycle. These goals now appear feasible as a result of recent design work exploiting a phenomenon, known as a traveling wave, that can attain high burn-ups without reprocessing. A traveling-wave reactor (TWR) breeds and uses its own fuel in place as it operates. Fueled almost entirely by depleted or natural uranium, such reactors would also require little initial enrichment. We have performed calculations demonstrating that TWRs can achieve burn-ups of ≥20%, which is four to five times that realized in current LWRs. Burn-ups of up to 50% appear feasible. The factors that contribute to these high burn-ups and the implications for materials design will be discussed.

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