US-based start-up Apollo Atomics, an MIT spinoff developing next generation pressurised water reactors (PWRs), has raised $31m in seed financing. The round was oversubscribed and led by Silicon Valley venture capital firm FCVC. Participants included Y Combinator, Telesoft Partners, Alumni Ventures, Robinhood Ventures, Nucleation Capital, Pelion VC, and Duke Capital Partners. Notable individual investors included Evan Meagher, Paul Graham, Philip Johnston, Matteo Franceschetti and Ray Rothrock.
Apollo was founded in 2025 by Assil Halimi, an MIT Nuclear Engineering PhD with extensive experience in reactor operations and advanced PWR design, and Drew Walker, a hard-tech founder and former White House director. The company has built and tested a working reactor-system demonstrator within MIT’s Department of Nuclear Science & Engineering to expand experimental validation of its hardware under prototypic commercial reactor conditions.
Apollo plans to develop three reactor systems: the 10 MWe A-10, the 50 MWe A-50 and the 300 MWe A-300 and is currently working on a 1 MWe demonstrator. The portfolio is designed to serve data centres, industrial facilities, utilities and other large energy users.
Rather than designing a completely new reactor type, Apollo is refining PWR technology, which already powers roughly 80% of the world’s nuclear fleet. The key change is a redesigned steam generator. In a traditional PWR, the steam generator is the single largest component. It dictates the enormous size of the heavy, thick-walled reactor pressure vessel and the surrounding reinforced concrete containment structure.
By threading the primary reactor coolant loop and secondary turbine loop through a dense, micro-channel block, Apollo maximises the surface area available for heat transfer in a minuscule space, shrinking the steam generator down to 5% of its original volume while maintaining identical thermal power output. This allows the entire nuclear steam supply system to collapse down into a compact, truck-transportable module. Apollo Atomics achieves this by replacing standard, multi-story tube bundles with a monolithic block of metal laced with thousands of needle-thin fluid channels.
The design uses existing low-enriched uranium fuel and established light-water nuclear supply chains, drastically reducing material and technology risks. By focusing on a single, high-impact hardware re-engineering problem rather than reinventing the fuel cycle, Apollo Atomics is positioning itself to bypass the massive delays that have traditionally crippled the advanced nuclear sector.
With its $31m seed round, Apollo is advancing its commercial timeline. The financing will support construction of the A-1, a 1 MWe commercial demonstrator facility; long-duration reliability testing; vertical integration of key manufacturing processes; expansion of engineering and operations capabilities; and continued engagement with the NRC.
Apollo submitted its regulatory engagement plan to the US Nuclear Regulatory Commission (NRC) earlier this year. By using a pre-licensed fuel configuration that has already successfully reached full-power criticality at MIT, Apollo is targeting fuel configuration authorisation by the end of 2026 to clear an easier path to commercial deployment by 2028.
The company claims to have already secured over 20 GWe of signed letters of intent in its commercial pipeline.
