NRC Finalizes Part 53 Rule, Creating New Voluntary Licensing Path for Nuclear Plants

NRC Chairman Ho Nieh called it "a historic milestone," and as of April 29, 2026, it becomes law: the agency's Part 53 final rule, published in the Federal Register on March 30, opens the first new voluntary nuclear licensing pathway in 37 years, one that an agency analysis estimated could save a single advanced reactor developer between $53.6 million and $68.2 million.

Part 53 is the first new set of regulations to address initial reactor licensing since 1989, when the NRC created Part 52, and the first major update to reactor licensing standards since 1956, when the Atomic Energy Commission issued Part 50. For the advanced reactor community, which has spent years navigating a rulebook written for light-water technology, that gap is the whole ballgame.

The rule's core departure from Parts 50 and 52 comes down to one fundamental shift: instead of asking every reactor design to fit a prescriptive framework built around conventional light-water reactors, Part 53 lets applicants define safety using probabilistic risk assessment and performance-based objectives. Under Part 53, applicants will no longer need to seek exemptions from light-water-based requirements. For a molten salt, sodium-cooled, or gas-cooled design, that exemption burden has historically added cost and review time before a project even reached substantive licensing work.

Acting Deputy Office Director for New Reactors Jeremy Bowen expects reactor designs under Part 53 to receive approval in 18 months or less, with application costs potentially reduced by half or more given the shorter review and added flexibility. The combined-license provisions supporting factory testing are a particular unlock for small modular and microreactor developers, whose manufacturing models depend on off-site component testing that the existing framework never cleanly accommodated.

The NRC completed Part 53 more than a year ahead of an end-of-2027 deadline set in the Nuclear Energy Innovation and Modernization Act of 2019. Bowen noted that several advanced reactor developers and potential applicants have already indicated interest in using Part 53 once it became available. The rule amends 24 parts of 10 CFR in total, with cross-references running through Part 26 and into the fee schedules at Parts 170 and 171, meaning submissions filed under the new path will touch a wide swath of the regulatory architecture.

Part 53 leaves Parts 50 and 52 fully intact. It is explicitly voluntary: developers building conventional light-water plants can stay on the existing rails without disruption, and Nieh noted that "with the addition of Part 53 to Part 50 and 52," America now has multiple options available to applicants and licensees pursuing new nuclear technology.

The start gun has fired, but the sprint is still ahead. Observers tracking the rule's progress note that effective implementation will depend on the speed and clarity of accompanying NRC guidance documents and on whether agency staffing keeps pace with a potential surge in pre-application and licensing activity. The pathway is open; how quickly the first applicants reach the finish line depends on the infrastructure that follows.