Antares Nuclear
Table of Contents

⚠ Disclaimer: This entry may be incomplete, out of date, or inaccurate. It is AI-maintained on a best-effort basis. Do not rely on it as a sole source — verify claims independently using the sources listed below.

Summary

Antares Nuclear is a Torrance, California microreactor developer founded in 2023 by Jordan Bramble. On June 4, 2026 its Mark-0 demonstration reactor achieved initial criticality at Idaho National Laboratory’s Materials and Fuels Complex — the first reactor to go critical under DOE’s Reactor Pilot Program, ahead of Valar Atomics, Deployable Energy, Aalo Atomics and Oklo. The reactor is a sodium heat-pipe-cooled, graphite-moderated design running TRISO fuel at 19.75% HALEU enrichment, with no pumps in the primary heat path.

Antares is the most defence-oriented company in this section. Its customer set is entirely governmental: the Air Force ANPI initiative (Joint Base San Antonio, April 2026), the Army’s Janus program (Fort Bragg, August 2026), and a stated NASA lunar fission surface power ambition. It has raised >$600M across four rounds**, most recently a **$470M Series C in July 2026 co-led by Paradigm and Caffeinated Capital, and in May 2026 signed what is billed as the world’s first multi-year commercial HALEU supply agreement, with Urenco.

Three things distinguish it from its criticality-cohort peers: it went first; its regulatory position is arguably the thinnest of the group (an NRC pre-application docket with a single “no review requested” engagement plan); and its Army work will be regulated by the Army, not the NRC or DOE — a third regime that sits outside civilian nuclear oversight entirely.

Key Facts

  • Founded: 2023 (seed closed November 2023)
  • HQ: Torrance, CA per the July 2026 Series C release; earlier sources say Redondo Beach, CA and the NRC lists Los Angeles — likely a relocation. Additional sites: Idaho Falls, ID and Aiken, SC
  • Legal entity: “Antares Nuclear, Inc.”; earlier filings use “Antares Industries”
  • Type: Private
  • CEO & Co-Founder: Jordan Bramble — systems engineering and physics (George Mason), statistics (Georgetown); prior work at the White House Office of Management and Budget. Other co-founders are not named in any public source
  • Chief Nuclear Officer: Dr. Rian Bahran (joined July 28, 2026) — former DOE Deputy Assistant Secretary for Nuclear Reactors; 10+ years Los Alamos; White House OSTP; PhD nuclear science & engineering, RPI
  • Reactor lineage: Mark-0 (zero-power test reactor, critical June 2026) → Mark-1 (first electricity-producing prototype, targeted 2027) → R1 (production microreactor, 100 kW – 1 MWe, deployments targeted 2028)
  • Reactor type: Sodium heat-pipe cooled, graphite-moderated microreactor; no pumps in the primary heat path
  • Fuel: TRISO compacts at 19.75% HALEU; fabricated by BWXT (Lynchburg, VA) since October 2025
  • Thermal rating: Not publicly disclosed for any variant
  • Criticality: June 4, 2026, INL Materials and Fuels Complex — first under the DOE Reactor Pilot Program; the 53rd reactor built at INL since 1951. Mark-0 has no power conversion system and no heat removal system — output was, per INL director John Wagner, “essentially no measurable energy output”
  • Funding: $8M seed (Nov 2023, Caffeinated Capital); $30M Series A (Oct 2024, Alt Capital + Caffeinated); $96M Series B (Dec 2025, $71M equity + $25M debt, led by Shine Capital); **$470M Series C (July 27, 2026, $370M equity + $100M debt, co-led by Paradigm and Caffeinated Capital)** with Point72 Ventures, Shine Capital, Industrious Ventures. Company total: “>$600M”. No valuation disclosed for any round
  • Regulatory: DOE Reactor Pilot Program (selected Aug 2025; PDSA Jan 2026, DSA April 6, 2026). NRC: pre-application only — docket 99902149, engagement since May 2025, a July 2025 Regulatory Engagement Plan marked “no review requested,” no application of any kind filed. Army Janus reactors will be “regulated by the Army,” contractor-owned and contractor-operated
  • Defence programmes: DAF ANPI — selected April 22, 2026 for proposed deployment at Joint Base San Antonio, TX (not a finalized contract); Army Janus — awarded August 26, 2026 for Fort Bragg, NC (three R1 units) under an Other Transaction Authority agreement
  • HALEU: Multi-year commercial supply agreement with Urenco, signed May 21, 2026 — but material comes from Urenco’s UK HALEU facility, which does not come online until 2031; near-term fuel is federally allocated HALEU downblended from NNSA scrap
  • Manufacturing: In-house; first 30–40 units planned at Torrance, CA; Series B targeted ~10 units/yr capacity. No external EPC named

What It Is / How It Works

Heat pipes instead of pumps. Antares’ core engineering claim is a primary heat-transport path with no moving parts. Sealed steel tubes containing liquid sodium run from the core outward; reactor heat vaporizes sodium at the hot end, the vapor travels to a heat exchanger, condenses, and returns to the core by capillary action through an internal wick. There is no pump, no valve, and no external power requirement in that loop, so the company argues cooling continues through a total station blackout. Combined with TRISO fuel — where each fuel kernel carries its own ceramic containment — the pitch is a reactor that is difficult to melt down and can run autonomously for years without refueling, in a package small enough to truck or airlift.

This is the same passive-heat-pipe concept pursued by NuCube Energy in this section and by Westinghouse’s eVinci, though implementations differ. The recurring technical objections are also common to the class: graphite moderators crack under sustained neutron flux, and sodium heat pipes scale poorly to higher power — which is why heat-pipe designs cluster at the sub-megawatt end and why the economics at that scale remain unproven.

The defence market is the whole thesis. Where Oklo, Aalo Atomics and X-energy are chasing hyperscaler datacenter load, Antares is building for forward operating bases, installation resilience and — eventually — lunar surface power. The customer has different requirements: transportability, autonomous operation with minimal staffing, tolerance for higher cost per kilowatt-hour, and indifference to grid interconnection. It also has a different regulatory posture, which is the most consequential structural fact about this company.

Three separate regulatory regimes, none of them commercial NRC licensing. Mark-0 ran under DOE authorization (PDSA → DSA → readiness review → startup approval under DOE-STD-1271). The Army’s Janus reactors will be Army-regulated, contractor-owned and contractor-operated. And NRC — the independent civilian safety regulator — has from Antares only a pre-application engagement plan submitted with “no review requested.” Executive Order 14299 mandates a reactor operating at a domestic military installation by September 30, 2028, and the Janus OTA structure is designed to reach that date. Whatever one concludes about the merits, none of these pathways produces an NRC licence, and Antares would need one to sell power to a civilian customer.

What criticality demonstrated. Very little, by the company’s own reactor’s construction. Mark-0 has no power conversion and no heat removal system; INL’s director confirmed there was “essentially no measurable energy output” and that “this is not electricity generation.” It validated core physics, neutronics and instrumentation. Edwin Lyman of the Union of Concerned Scientists was blunter: “This stunt is a rudimentary first step that has absolutely no bearing on whether the Antares reactor will be safe or commercially viable,” and specifically disputed DOE’s characterization that the test “confirms the reactor can operate safely.”

Notable Developments

  • 2026-08-26: US Army Janus Program award — Antares selected for Fort Bragg, NC (three R1 units) alongside BWXT (Fort Campbell), General Atomics (Fort Hood), Radiant Industries (Fort Benning) and Westinghouse (Fort Drum). Up to $2.2B combined across five vendors, FY2027–2031, via milestone-based OTAs; per-company value not broken out. (army.mil; POWER; Defense News)
  • 2026-07-28: Dr. Rian Bahran joins as Chief Nuclear Officer from his post as DOE Deputy Assistant Secretary for Nuclear Reactors. (BusinessWire)
  • 2026-07-27: **Series C — $470M** ($370M equity + $100M debt), co-led by Paradigm and Caffeinated Capital. ([BusinessWire](https://www.businesswire.com/news/home/20260727569769/en/Antares-Raises-$470M-Series-C-to-Deploy-Nuclear-Microreactors-for-Critical-Missions); TechCrunch)
  • 2026-06-04: Mark-0 achieves initial criticality at INL — the first reactor to go critical under the DOE Reactor Pilot Program. (DOE; ANS; WNN)
  • 2026-05-21: Urenco HALEU supply agreement — billed as the world’s first multi-year commercial HALEU supply contract. Term, tonnage and pricing undisclosed; supply originates from Urenco’s UK facility, online 2031. (BusinessWire; NucNet)
  • 2026-04-22: Selected for proposed deployment at Joint Base San Antonio under the Department of the Air Force ANPI initiative — explicitly not a finalized contract. (BusinessWire; ANS)
  • 2026-04-06: DOE approves the Documented Safety Analysis for Mark-0 (PDSA approved January 2026). (BusinessWire)
  • 2025-12-02: Series B — $96M, led by Shine Capital. (ANS)
  • 2025-10: BWXT begins TRISO fuel fabrication for Mark-0.
  • 2025-08: Selected for the DOE Reactor Pilot Program.
  • 2024-10-31: Series A — $30M. **2024-09:** DOE GAIN voucher for design validation. **2023-11-01:** Seed — $8M.

Key People

Jordan Bramble — CEO & Co-Founder

  • LinkedIn: linkedin.com/in/jordanbramble
  • Background: Degrees in systems engineering and physics (George Mason) and statistics (Georgetown); prior work at the White House Office of Management and Budget; launched Antares in 2023
  • Notes: ⚑ No other co-founder is named in any public source, and Antares publishes no board of directors. Investors with likely board representation include Shine Capital’s Alex Hartz (led Series B), Paradigm’s Alana Palmedo and Caffeinated’s Varun Gupta (quoted on Series C), but board seats are not stated anywhere.

Dr. Rian Bahran — Chief Nuclear Officer

  • LinkedIn: linkedin.com/in/rianbahran
  • Background: Former DOE Deputy Assistant Secretary for Nuclear Reactors; 10+ years at Los Alamos National Laboratory; senior advisor to the Under Secretary of Defense for Policy (SecDef Medal for Exceptional Public Service); Assistant Director for Nuclear Technology & Strategy at the White House OSTP; PhD nuclear science & engineering, RPI
  • Notes: ⚑ Revolving door: Bahran was quoted in his capacity as DOE Deputy Assistant Secretary praising Antares in the company’s own April 6, 2026 DSA-approval press release, and joined the company roughly four months later. Recorded because the DOE authorization pathway Antares uses is administered by the office he came from.

Matt Griffin — Head of Nuclear Affairs and Licensing

  • Background: Signs Antares’ NRC correspondence; named in NRC docket materials

Other named leadership

Mark Massie (Chief Engineer), Will Madsen (Head of Mission Engineering), Nader Satvat (Head of Nuclear Engineering), Tom Mancinelli (Strategy & Policy), Alec Todryk (Finance), Christian Kalin (Operations), Doug Crawford (Manufacturing & Test Engineering), Scott Walsh (Reactor Hardware Engineering), Jason Andrus (Nuclear Ops & Regulatory), Reuven Fridmar (Talent). Public bios are not published for these roles.

People — Last Reviewed: 2026-08-27

Supply Chain Position

Layer Detail
TRISO fabrication BWXT (Lynchburg, VA) — fabricating for Mark-0 since October 2025; fuel specification maturity credited to Project Pele heritage
HALEU (near term) DOE-allocated, reported as downblended NNSA scrap material
HALEU (commercial) Urenco, multi-year agreement signed May 21, 2026 — but from Urenco’s UK HALEU facility, online 2031
Coolant Liquid sodium in sealed heat pipes; supplier not disclosed
Moderator Graphite; supplier not disclosed
Manufacturing In-house, Torrance CA; first 30–40 units; ~10 units/yr targeted capacity
EPC None named
Sites INL Materials and Fuels Complex (test); Fort Bragg NC (Janus); Joint Base San Antonio TX (ANPI, proposed)
Regulatory DOE authorization (Mark-0); Army regulation (Janus); NRC pre-application only

⚑ A three-year fuel gap. Antares targets first production deployments in 2028, but its commercial HALEU contract draws on a Urenco UK facility that does not open until 2031. Bramble’s own framing acknowledges the bridge — the Urenco deal covers “when we scale beyond material allocated by the federal government.” Until then Antares depends on DOE-allocated HALEU downblended from NNSA scrap, a finite and politically allocated resource that Oklo, X-energy and Kairos Power are also drawing against. This is the sharpest supply-chain exposure of any company in this section’s 2026 criticality cohort.

⚑ BWXT concentration deepens. Antares joins Kairos, X-energy, Radiant Industries and NuCube in depending on BWXT’s Lynchburg TRISO line — and separately competes with BWXT Advanced Technologies for Army Janus work (BWXT won Fort Campbell). BWXT is simultaneously Antares’ sole fuel fabricator and a direct competitor for its primary customer.

⚑ Two different Urenco entities in this section. Antares contracts for HALEU from Urenco’s UK plant; Deep Fission contracts for LEU from Urenco USA (Eunice, NM); Aalo Atomics also uses Urenco USA. Different products, different facilities, very different timelines — do not conflate.

Claim Verification

Claim: Mark-0’s criticality demonstrated the reactor “can operate safely”

Status: Disputed — DOE’s characterization was challenged directly

Supporting: DOE announced the milestone as the first advanced reactor criticality under the Reactor Pilot Program and framed it as confirming safe operation.

Refuting / questioning: INL Director John Wagner stated the reaction “was sustained at essentially no measurable energy output. This is not electricity generation.” Mark-0 has no power conversion system and no heat removal system at all. Edwin Lyman (Union of Concerned Scientists) called the test “a rudimentary first step that has absolutely no bearing on whether the Antares reactor will be safe or commercially viable,” and specifically disputed DOE’s safety characterization as false. DOE Assistant Secretary Ted Garrish publicly acknowledged programme skeptics at the announcement.

Summary: Criticality validated core physics and instrumentation. It says nothing about thermal performance, materials behaviour, or safety under power — and the DOE framing overstates it.

Claim: R1 power rating, deployment dates, and total funding

Status: Company-sourced only

Supporting: All figures — 100 kW–1 MWe for R1, “years without refueling,” ~10 units/yr Torrance capacity, “>$600M total raised,” the 2027 Mark-1 and 2028 deployment dates — come from Antares press releases.

Refuting / questioning: No independent verification exists for any of them. The thermal rating (MWt) of every Antares variant is undisclosed, as is the valuation of every funding round, the identity of the co-founders, the board, the Urenco contract terms, and the per-company Janus dollar figure.

Summary: The funding rounds themselves are well documented by law-firm and newswire records; the technical and schedule claims are not independently verified.

Claim: Janus and ANPI are contracts

Status: Both are pre-contractual instruments

Supporting: Both are real, competitive government selections with named installations.

Refuting / questioning: The Air Force ANPI selection is explicitly for proposed deployment, not a finalized contract. The Army Janus awards are Other Transaction Authority agreements with milestone-gated funding that the Army may reallocate between vendors — not firm production contracts. The $2.2B figure is the combined five-vendor ceiling over FY2027–2031, not an Antares award.

Summary: Real government traction, but do not cite a dollar figure for Antares or describe either as a production contract.

Risk & Skepticism Notes

  • The thinnest NRC position in the cohort. Antares’ entire NRC file is a pre-application docket opened May 2025 and one Regulatory Engagement Plan submitted with “no review requested.” Nothing has been applied for. Its three operating pathways — DOE authorization, Army regulation, and eventual NRC licensing — currently include exactly zero NRC instruments.
  • Army self-regulation is a genuinely novel arrangement. Janus reactors will be contractor-owned, contractor-operated and Army-regulated, outside both NRC civilian licensing and the DOE authorization framework. There is no established precedent for commercial microreactors operating on this basis, and it is the mechanism by which the September 30, 2028 EO 14299 deadline becomes reachable.
  • No commercial customer. Every Antares relationship is with the federal government. There is no PPA, no datacenter agreement, and no civilian offtake — which means the company’s revenue path runs entirely through programmes whose funding is milestone-gated and politically contingent.
  • The 2031 fuel gap (above) is the concrete near-term execution risk.
  • Undisclosed basics. No valuation, no thermal rating, no board, no named co-founders. For a company that has raised over $600M, this is an unusual amount of opacity.

Sources

See Also

Nuclear section overview: Nuclear Energy Research — deployment status tracker, DOE Reactor Pilot Program context, and HALEU/TRISO supply chain notes.

The 2026 criticality cohort: Valar Atomics (second), Deployable Energy (third), Aalo Atomics (fourth), Oklo (fifth).

Fellow Army Janus awardee: Radiant Industries — Fort Benning, up to $750M and 15 Kaleidos units by 2030.

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