Is It Time for the United States to Reconsider Transmutation for Spent Nuclear Fuel?

The United States is considering a major expansion of nuclear capacity by 2050. We examine how such growth affects geologic repository requirements under a 60-year spentfuel cooling premise and whether targeted partitioning and transmutation (P&T) can relax the thermal constraints that dominate repository sizing. Using isotopic decay modeling, Yucca Mountain–calibrated thermal spacing, and bounding cost scaling, we compare once-through, Pu-only recycle, fast reactor transuranic recycle, and americium-focused strategies.We evaluate accelerator-driven systems (ADS) and molten salt subcritical systems sized by energetic throughput and reliability targets. We consider the safeguards-by-design immobilization of Pu/Np by avoiding pure Pu streams and binding Pu and Np in durable ceramics with neutron absorbers, reducing the risk of creating easy Pu extraction from a future “plutonium mine.”Under our assumptions, removing americium (with curium coprocessing) and setting aside 137Cs for decay reduces long-term package power and increases areal loading, shrinking the total repository footprint by orders of magnitude relative to once through. Illustrative system costs indicate that an ADS Am burner is significantly less costly than multirepository pathways, especially when combined with Pu burning in fast reactors.We outline key engineering risks (beam trip tolerance, corrosion/redox control, 37Cl enrichment) and policy trade-offs (interim storage, safeguards). We conclude that staged demonstrations of americium-focused P&T merit priority to derisk thermal loading, cost, and safeguards outcomes. Our analysis leads us to strongly recommend that a well-funded research and development program be initiated by the U.S. Department of Energy to further understand the benefits, as well as the performance, cost, technical, and political challenges, posed by partitioning and partially transmuting spent nuclear fuel.