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Advanced reactors in the US: SMRs and microreactors

The standing record of US small modular reactors and microreactors: what has gone critical under DOE, what the NRC has permitted, and the rules, military buyers and fuel supply that decide what comes next.

Updated · first published · 9 min read

Where things stand

As of October 8, 2026, the US has one commercial small modular reactor cleared for construction and a summer's worth of test reactors that went critical under Department of Energy authority. None of these projects yet holds an NRC license to operate.

DOE moved first. It counted five advanced reactors that reached criticality under its authorization between June 4 and August 5: Antares Nuclear's Mark-0, Deployable Energy's Unity and Aalo Atomics' Critical Test Reactor at Idaho National Laboratory, Valar Atomics' Ward 250 in Utah and Oklo's Groves isotope test reactor in Texas. Westinghouse completed zero-power criticality testing of its eVinci design in Nevada on August 24. Next up: INL's MARVEL, whose dry criticality INL anticipates in December, and Radiant's Kaleidos, whose full-power campaign was targeted for the third quarter; Radiant had announced no criticality as of October 8.

The NRC track is slower and bigger. On September 28 the NRC issued TVA a construction permit for a 300 MWe BWRX-300 at Clinch River, Tennessee, which the agency says clears the way for the nation's first commercial SMR. TerraPower's 345 MWe Kemmerer Unit 1 in Wyoming received its permit decision on March 9. Kairos Power holds permits for its Hermes and Hermes 2 test facilities, and Abilene Christian University one for Natura Resources' MSR-1 molten salt reactor. Under review: Long Mott Energy's four-module, 320 MWe Xe-100 plant in Texas, the first part of a phased application for two SMR-300 units at Palisades in Michigan, and the University of Illinois' KRONOS research microreactor. At Palisades, the NRC has already allowed permanent excavation walls to be built before any limited work authorization. NuScale's 462 MWe US460 design won standard design approval in May 2025.

The rules are being rewritten on a deadline. Executive Order 14300 gave the NRC until November 23, 2026 for final rules, and the technology-inclusive Part 53 took effect April 29. Proposals reaching this class include one letting commercial applicants draw on a design's prior DOE or Department of War authorization, a new Part 57 for "rapid licensing" of microreactors and reactors with comparable risk profiles, and a broad reactor package open for comment until November 9. The NRC's tracker estimates two of those three final rules after the deadline.

The first customer wears a uniform. The Army's Janus Program picked five vendors on August 26 for vendor-owned microreactors at five bases, for up to a combined $2.2 billion over fiscal 2027 to 2031. A Navy unit at Crane, Indiana, is planned no later than September 2028, with no vendor named, and Executive Order 14299 wants an Army-regulated reactor operating on a base by September 30, 2028.

Fuel gates all of it. DOE says HALEU "is not currently available from domestic suppliers." Centrus expects its first new enrichment capacity by 2029 and will begin HALEU deliveries to Radiant before the end of the decade; Standard Nuclear, which calls itself the only US company with industrial-scale TRISO fabrication, has a binding supply agreement with Antares.

Timeline

202420252026Oct 6, 2026Oct 1, 2026Sep 28, 2026Sep 24, 2026Sep 21, 2026Sep 18, 2026Sep 11, 2026Sep 9, 2026Sep 9, 2026Sep 8, 2026Sep 3, 2026Sep 3, 2026Aug 28, 2026Aug 27, 2026Aug 26, 2026Aug 24, 2026Aug 20, 2026Aug 13, 2026Aug 6, 2026Aug 5, 2026Jul 23, 2026Jul 4, 2026Jul 1, 2026Jun 30, 2026Jun 18, 2026Jun 4, 2026May 1, 2026Apr 2, 2026Mar 31, 2026Mar 30, 2026Mar 9, 2026Dec 31, 2025Dec 2, 2025Aug 12, 2025May 23, 2025Mar 31, 2025Nov 21, 2024Sep 16, 2024Dec 14, 2023
39 dated events, 2023 to 2026. Jump to 2026, 2025, 2024, 2023.
  1. 2026

  2. Idaho National Laboratory said DOE's Idaho Operations Office had approved MARVEL's final documented safety analysis, authorizing a dry, near-zero-power criticality configuration, and that criticality is "anticipated to occur in December" (INL).

    Coverage DOE clears MARVEL microreactor's final safety analysis for dry criticality

  3. The NRC began four weekly Federal Register notices of receipt for the first part of Holtec's phased construction permit application, with a limited work authorization request, for Pioneer Units 1 and 2 at Palisades (Federal Register).

  4. The NRC issued Construction Permit CPAR-2 to TVA for Clinch River Nuclear Unit 1, a BWRX-300, setting construction completion between October 1, 2031 and September 30, 2032 (permit). The NRC's September 29 release says the permit clears the way for "the nation's first commercial small modular reactor" after a 14-month review (NRC).

    Coverage NRC issues TVA a construction permit for a 300 MW BWRX-300 at Clinch River

  5. The NRC's proposed rule "Regulatory Enhancements for Reactor Licensing, Decommissioning, and Operational Oversight" was published at 91 FR 60702, with comments due November 9, 2026 (Federal Register).

    Coverage NRC's proposed reactor rule published; comments due November 9

  6. Kairos Power said Samsung C&T agreed to provide up to $100 million in direct investment and in-kind engineering, subject to regulatory approvals, for the Hermes 2 demonstration plant in Oak Ridge (Kairos Power).

    Coverage Samsung C&T commits up to $100M of investment and engineering to Kairos

  7. Natura Resources received FLiBE salt from Oak Ridge National Laboratory, via INL, for the MSR-1 being built at Abilene Christian University (Natura).

    Coverage Natura receives Oak Ridge's 1960s FLiBE salt for its Abilene reactor

  8. The NRC announced a proposed "broad overhaul" of its reactor licensing and oversight rules under Executive Order 14300 (NRC).

    Coverage NRC proposes rule package for existing reactors and new applicants

  9. The Department of War announced a commercially owned and operated Micro Modular Reactor at Naval Weapons Station Crane, Indiana, no later than September 2028, executed through the Army's Janus Program (Department of War).

    Coverage Department of War plans shore-based Navy microreactor at Crane by 2028

  10. Centrus announced, in an exhibit to a Form 8-K, a definitive multi-year contract to supply HALEU for multiple Radiant Kaleidos microreactors, with deliveries to begin before the end of the decade (Form 8-K exhibit).

    Coverage Centrus signs HALEU supply contract for Radiant's Kaleidos microreactors

  11. A University of Colorado Boulder preprint argued that operating and fuel costs, not investment costs, make SMRs at advertised costs uneconomical in US power markets (arXiv).

    Coverage CU Boulder preprint says SMR operating costs, not capex, drive poor returns

  12. Westinghouse's eVinci test reached zero-power criticality at 663°C at the National Criticality Experiments Research Center in Nevada (Westinghouse).

    Coverage Westinghouse eVinci reaches zero-power criticality at 663°C

  13. Deep Fission lowered a 20-foot, non-nuclear prototype reactor canister to 100 feet in a 34-inch borehole and retrieved it (Deep Fission).

    Coverage Deep Fission lowers full-size canister replica 100 feet into a borehole

  14. The NRC granted Palisades SMR, LLC an exemption allowing construction of permanent support-of-excavation walls for Pioneer Units 1 and 2 before a limited work authorization (Federal Register).

  15. Standard Nuclear announced a binding agreement to supply Antares a minimum of one and up to eight metric tons of uranium in TRISO fuel through 2035 (Form 8-K exhibit).

    Coverage Standard Nuclear to supply Antares up to eight tons of TRISO fuel

  16. The Army's Janus Program selected Antares, BWXT, General Atomics, Radiant and Westinghouse for microreactors at five bases, up to a combined $2.2 billion over fiscal 2027 to 2031 (Army).

    Coverage US Army awards up to $2.2 billion for microreactors at five bases

  17. Westinghouse completed zero-power criticality testing of its eVinci design in Nevada (Westinghouse).

    Coverage Five US microreactor designs went critical in the summer of 2026

  18. The NRC noticed the mandatory (uncontested) hearing on Long Mott's construction permit application for September 22, 2026, in Port Lavaca, Texas, with the hearing record open for comments until October 6 (Federal Register).

  19. Radiant said its 1 MWe Kaleidos had left El Segundo, California for INL's DOME test bed, with a minimum 150-hour continuous full-power run targeted for the third quarter of 2026 (Radiant).

  20. Deep Fission said DOE had approved the Nuclear Safety Design Agreement for its Gravity reactor under the Reactor Pilot Program, as it advances a commercial pilot project in Parsons, Kansas (Deep Fission).

  21. Oklo's Groves Isotope Test Reactor reached criticality in Lockhart, Texas, the fifth DOE-authorized advanced reactor to do so that summer (DOE).

  22. DOE made a conditional commitment of HALEU for Radiant's planned microreactor at Buckley Space Force Base, saying HALEU "is not currently available from domestic suppliers" (DOE).

  23. Aalo Atomics' Critical Test Reactor reached criticality at 12:20 a.m. Mountain time (Aalo).

  24. Centrus finalized a $900 million DOE task order for large-scale HALEU production capacity; it expects the first new capacity online by 2029 (Centrus).

  25. Deployable Energy's Unity reached criticality at INL under DOE's Nuclear Energy Launch Pad, the third DOE-authorized advanced reactor to do so (DOE).

  26. Valar Atomics' Ward 250 completed a zero-power criticality demonstration in Emery County, Utah, which DOE calls the first DOE-authorized reactor built outside a national laboratory (DOE).

  27. Antares Nuclear's Mark-0 completed a zero-power criticality demonstration at INL, the first under DOE's Reactor Pilot Program (DOE).

  28. The NRC proposed a new Part 57 for licensing microreactors and other reactors with comparable risk profiles; comments closed June 15 (Federal Register).

  29. The NRC proposed letting commercial applicants leverage prior DOE or Department of War authorizations of demonstration reactors; comments closed May 4 (Federal Register).

  30. The University of Illinois applied for a construction permit for its KRONOS research microreactor, based on NANO Nuclear technology; the NRC docketed it May 18 (NRC).

  31. The NRC published Part 53, its risk-informed, technology-inclusive licensing framework, effective April 29 (Federal Register).

  32. The NRC recorded its construction permit decision for TerraPower's 345 MWe Kemmerer Unit 1 in Wyoming (NRC), after the Commission authorized staff on March 4 to issue it (NRC release).

  33. 2025

  34. Palisades SMR, LLC submitted the first part of a phased construction permit application, with a limited work authorization request, for two SMR-300 units at Palisades (NRC).

  35. DOE selected TVA and Holtec for $400 million each toward first SMR plants at Clinch River and Palisades (DOE), and BWXT said a full core of TRISO fuel for the Project Pele microreactor had arrived at INL, with formal system testing planned as early as 2027 (BWXT).

  36. DOE selected 11 advanced reactor projects for its Reactor Pilot Program (DOE).

  37. Executive Order 14299 set a September 30, 2028 deadline for an Army-regulated reactor on a military base (Federal Register), and Executive Order 14300 ordered the NRC's "wholesale revision" of its regulations (Federal Register).

  38. Long Mott Energy applied for a construction permit for a four-module Xe-100 plant in Calhoun County, Texas (NRC).

  39. 2024

  40. The NRC issued Kairos Power construction permits for the Hermes 2 test reactor facility (NRC).

  41. The NRC issued Abilene Christian University a construction permit for its Molten Salt Research Reactor (NRC).

  42. 2023

  43. The NRC issued Kairos Power a construction permit for the Hermes test reactor in Oak Ridge (NRC).

Next milestone

  • 2026-10-31: NRC target for the draft environmental impact statement on the Palisades SMR-300s.
  • 2026-11-04: NRC tracker's estimated final rule on DOE- and War-authorized designs.
  • 2026-11-09: Comments close on the NRC's reactor licensing enhancements rule.
  • 2026-11-23: Executive Order 14300's 18-month deadline for NRC final rules.
  • 2027-01-26: NRC tracker's estimated final Part 57 microreactor rule.
  • 2028-09-30: Executive Order 14299's deadline for an Army-regulated reactor on a base.

Two of the three rules that matter most here are on course to miss the executive order's November 23 deadline. The NRC's rulemaking tracker estimates the final rule on DOE- and War-authorized designs for November 4, but the microreactor rule for January 26, 2027 and the reactor package for March 31, 2027; comments on that package close November 9 on docket NRC-2025-1138. On the licensing side, the NRC's Long Mott page targets a final safety evaluation in November 2026, with the permit decision still "TBD"; the NRC scheduled the mandatory hearing for September 22 in Port Lavaca, Texas, and kept the record open for comments until October 6. Its Palisades page targets the draft environmental impact statement for October 31. On the DOE side, watch INL for MARVEL's December dry criticality and Radiant for word on Kaleidos, whose third-quarter target has passed. The Crane reactor still needs a vendor, and the Army says it continues to drive toward the September 2028 target in Executive Order 14299.

This is a maintained page: it is revised as the record changes, and every revision is reviewed before it goes live. Dates in the text are the dates the facts hold for, not the date you are reading it.

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