The Nuclear Regulatory Commission published a proposed rule today that could fundamentally reshape how the United States licenses small nuclear reactors. Known as Part 57, the framework is designed specifically for microreactors and other reactors with comparable risk profiles, offering a licensing pathway that the agency says could compress approval timelines to as little as six to twelve months.
The rule, published in the Federal Register, establishes what the NRC calls a risk-informed and performance-based regulatory framework for rapid licensing of first-of-a-kind microreactors and high-volume deployment of standardized designs. The comment period runs through June 15, 2026.
A Framework Tailored to Small Machines
While the proposed rule does not explicitly set a power threshold, NRC Chairman Ho Nieh has indicated that Part 57 is intended for reactors generating 100 megawatts electric or less. For context, small modular reactors typically fall in the 50 to 300 megawatt range, and conventional light-water reactors often exceed a gigawatt.
"They're small machines, they're simple machines," Nieh said at a press briefing. "We are looking at designs here that have very simple safety cases, where there's not a lot of complex safety equipment that needs to activate during an event."
The NRC projects that Part 57 will save the agency and industry between $3.76 billion and $11.84 billion, primarily by reducing exemption requests and streamlining reviews. Those estimates depend on discount rate assumptions, but either end represents a substantial reduction in the regulatory burden that has historically made nuclear projects financially precarious.
What the Rule Actually Does
Several provisions distinguish Part 57 from the existing licensing frameworks in Parts 50, 52, and the recently finalized Part 53. The proposed rule allows applicants to request approval for entire fleets of identical reactors under a single application. It permits the use of alternative design standards and operational programs suited to novel reactor types. It streamlines environmental reviews for projects with demonstrated minimal impacts. And it creates a general license pathway that would allow construction of certain components to begin before the NRC issues a formal permit.
The rule also introduces a graded approach to site characterization, allowing applicants to leverage existing data from federal, state, or other organizations rather than conducting exhaustive new studies for every deployment location.
Policy Pressure From Multiple Directions
Part 57 responds to overlapping mandates from Congress and the executive branch. Section 208 of the ADVANCE Act, signed into law in 2024, required the NRC to develop risk-informed strategies for microreactor licensing by July 2027. Executive Order 14300, issued by President Trump in May 2025, went further, directing the NRC to establish a process for high-volume licensing of microreactors and modular reactors, including consideration of general licenses for certain reactor components.
The executive order also set aggressive timelines: the NRC was required to issue this proposed rule by February 2026, with a final rule due by November 2026. The proposed rule arrives slightly behind that schedule but well within the statutory deadline set by the ADVANCE Act.
Context and Skepticism
The nuclear industry has spent years asking for exactly this kind of regulatory flexibility. Microreactors are being developed for applications ranging from data center power to remote military installations to industrial process heat. The Department of War's Project Janus aims to deploy microreactors at several military bases, and the Department of Energy has selected multiple reactor projects under its Reactor Pilot Program.
Whether Part 57 delivers on its promise will depend on implementation. Faster timelines mean little if applicants cannot navigate the framework, or if safety reviews get compressed in ways that invite legal challenges. The rule maintains the NRC's core safety requirements; it simply adapts the process to match the lower consequence potential of these smaller designs.
Comments on the proposed rule can be submitted through Regulations.gov under Docket ID NRC-2025-0379.
