Title: Evaluating Advanced Nuclear Fission Technologies for Future Decarbonized Power Grids

Abstract: In the coming decades, the United States aims to undergo an energy transition away from fossil fuels and toward a fully decarbonized power grid. There are many pathways that the US could pursue toward this objective, each of which relies on different types of generating technologies to provide clean and reliable electricity. One potential contributor to these pathways is advanced nuclear fission, which encompasses various innovative nuclear reactor designs. However, little is known about how cost-competitive these reactors would be compared to other technologies, or about which aspects of their designs offer the most value to a decarbonized power grid. We employ an electricity system optimization model and a case study of a decarbonized U.S. Eastern Interconnection circa 2050 to generate initial indicators of future economic value for advanced reactors and the sensitivity of future value to various design parameters, the availability of competing technologies, and the underlying policy environment. These results can inform long-term cost targets and guide near-term innovation priorities, investments, and reactor design decisions. We find that advanced reactors should cost \$5.1-\$6.6/W to gain an initial market share (assuming 30 year asset life and 3.5-6.5% real WACC), while those that include thermal storage in their designs can cost up to \$5.5-\$7.0/W (not including cost of storage). Since the marginal value of advanced fission reactors declines as market penetration increases, break-even costs fall around 19% at 100 GW of cumulative capacity and around 40% at 300 GW. Additionally, policies that provide investment tax credits for nuclear energy create the most favorable environment for advanced nuclear fission. Stakeholders and investors should consider these findings when deciding which technologies to consider for decarbonizing the US power grid.