The United States has taken a step toward a 21st-century renaissance in civilian nuclear power as the Nuclear Regulatory Commission (NRC) has given the go-ahead for TerraPower's Natrium Gen IV reactor to begin construction – the first such approval for a US reactor in a decade.
Once a global leader in nuclear power, the US created many of the Generation I and Generation II reactor designs on which much of today’s nuclear fleet is based. However, in the 1970s there was a major shift in American civilian nuclear policy. Nuclear fuel reprocessing and fast breeder reactor programs were terminated, the environmental movement – broadly hostile to nuclear power – gained influence over federal policy, and the Three Mile Island accident in 1979 severely damaged public confidence in nuclear energy.
As a result, the Energy Reorganization Act of 1974 was passed, followed by the Kemeny Commission investigation after the Three Mile Island incident in 1979. Control of the US civilian nuclear program shifted from the Atomic Energy Commission to the newly formed Nuclear Regulatory Commission (NRC), whose mandate focused primarily on safety rather than the promotion of nuclear power development.
The combination of increasingly complex regulations, long approval timelines, high costs, and frequent legal challenges from activist groups dramatically slowed new nuclear projects.
As a result, no new reactors were built in the United States for decades, and the last new reactor application approval occurred roughly ten years ago.
Now, the US government is looking to revive the nuclear sector with a more streamlined regulatory process aimed at encouraging the construction of new plants while maintaining safety standards.
A key example is the Natrium Demonstration Project for Kemmerer Power Station Unit 1 in Kemmerer, Wyoming. The plant is being developed by US SFR Owner, LLC (USO), a special-purpose vehicle and wholly owned subsidiary of TerraPower. A participant in the US Department of Energy’s Advanced Reactor Demonstration Program (ARDP), construction on the plant’s non-nuclear civil engineering components has been underway since 2024. With the NRC’s approval, work on the nuclear portions of the facility can now begin.
As a Generation IV reactor, Natrium is notable because it will be the first non-light-water reactor built in the United States since the 1980s. The project has also progressed at an unusually rapid pace for American nuclear development. The technical design review was completed in under 18 months, the formal application was accepted in May 2024, the safety evaluation was issued in December 2025, and the environmental impact statement was finalized in October.
However, approval for construction is only part of the process. Once the reactor is completed, the operator must still apply for a separate operating license before the plant can begin generating power.
The Natrium reactor is a significant advance on conventional designs in both its concept and layout. It what's called a fast-neutron reactor, meaning it does not slow neutrons using moderators such as water or graphite. Instead, neutrons remain at high energies, which requires the fuel to be enriched to higher levels – up to 19.75% compared with roughly 5% for typical light-water reactors.
Water is replaced with liquid sodium coolant, which melts at around 1,616 °F (880 °C) and is transparent to neutrons. The sodium circulates around the fuel at near-atmospheric pressure, eliminating the need for the massive high-pressure containment vessels required in traditional light-water reactors.
This configuration allows higher operating temperatures and improves thermal efficiency to about 41%, compared with roughly 31% for conventional reactors. It also enables more complete fuel burnup and potentially allows certain forms of nuclear waste to be used as fuel.
According to TerraPower, the design also offers safety advantages. Liquid sodium can circulate naturally through the system even if pump power is lost, providing passive cooling. If the reactor core temperature rises, the fuel expands, automatically reducing the nuclear reaction rate.
Another distinctive feature is the plant layout. The reactor itself is separated from the power-generation system. Heat from the reactor is carried by a secondary sodium loop to intermediate heat exchangers, which then transfer energy to a molten-salt loop connected to thermal storage tanks.
These molten-salt tanks act as energy buffers. While the reactor operates at a steady output of 840 MWt, stored heat can be released to steam turbines as needed to meet fluctuations in electricity demand. This flexibility could help stabilize power grids increasingly influenced by intermittent renewable energy sources.
"This is a historic step forward for advanced nuclear energy in the United States and reflects our commitment to delivering timely, predictable decisions grounded in a rigorous and independent safety review," said NRC Chairman Ho Nieh.
Source: NRC
