Apollo Atomics, a Cambridge-based nuclear startup founded in 2025, announced Thursday it raised $31 million in seed funding to develop compact reactors it says can be deployed in less than two years. The round was led by FCVC, with Y Combinator, Telesoft Partners, and several venture firms participating.
The August 20 financing drew backing from an eclectic mix of investors that included Y Combinator co-founder Paul Graham, nuclear industry veteran Ray Rothrock, and Robinhood Ventures. Alumni Ventures, Nucleation Capital, Pelion VC and Duke Capital Partners also joined. The company characterized demand as "substantially oversubscribed," though it declined to specify by how much.
Founded in 2025 by MIT nuclear engineering PhD Assil Halimi and Drew Walker, a former electric vehicle executive, Apollo is entering a suddenly crowded field of startups racing to supply nuclear power to energy-hungry data centers. What distinguishes the company, according to Halimi, is a redesigned steam generator that the firm claims achieves roughly 10 times the power density of conventional systems.
Halimi's doctoral research at MIT's Department of Nuclear Science & Engineering focused on high power-density small modular reactors and advanced fuels. She won the department's Del Favero Thesis Prize in July 2026. Walker brings manufacturing experience from scaling production at an electric truck company and previously founded an electric boat venture.
Rethinking the Steam Cycle
The technical heart of Apollo's pitch centers on what the company describes as a fundamental reimagining of the steam generator, typically the bulkiest component in a nuclear plant's steam cycle. Apollo said the redesign shrinks the overall reactor footprint by approximately 40 times compared to traditional plants, making the units small enough to ship on standard flatbed trucks.
The systems are factory-built, the company said, and rely on commercial-grade low-enriched uranium fuel and existing light water reactor supply chains. That supply chain compatibility could prove critical. Many advanced reactor designs require custom fuel types that don't yet have established production infrastructure.
Apollo's product roadmap envisions three models: the A-10 (10 megawatts electric), the A-50 (50 MWe), and the A-300 (300 MWe), targeting data centers, industrial customers, and utilities respectively. Before scaling to those sizes, the company plans to build the A-1, a 1-megawatt commercial demonstrator. Apollo said its design builds on more than 15 years of MIT research into compact steam generator concepts for high power-density integral pressurized water reactors.
Whether that timeline proves realistic remains an open question. Nuclear startups have historically struggled with development cycles that stretch far longer than initial projections.
Navigating the NRC
Apollo submitted a regulatory engagement plan to the Nuclear Regulatory Commission earlier this year, according to the company. It's seeking NRC authorization by the end of 2026 for commercial use of what it describes as a fuel configuration that has already reached criticality at full power. A construction permit application is targeted for 2028, per an April press release.
In April, the startup announced a research partnership with MIT's Department of Nuclear Science and Engineering. The collaboration focuses on full two-loop testing under reactor-like conditions to generate validation data for licensing submissions. Apollo said it built and tested a working reactor-system demonstrator inside MIT's nuclear engineering facilities.
The company has assembled a notable advisory board. Christopher Hanson, who chaired the Nuclear Regulatory Commission from 2021 to 2025, signed on as an advisor. Also advising: Ray Rothrock (who is both an investor and advisor), MIT Professor Koroush Shirvan (Halimi's former doctoral advisor), and Mike Rencheck, who led Canadian utility Bruce Power as CEO through June 2024 and now serves as executive vice-chair. Apollo said other senior utility executives joined the board but wouldn't name them.
Customer interest, at least on paper, appears strong. Apollo said it has signed letters of intent representing more than 20 gigawatts in its commercial pipeline. The company wouldn't disclose customer names or provide contract specifics.
Following the AI Power Surge
The fundraise lands as data center operators scramble to secure power for artificial intelligence workloads. EPRI projected in March that US data centers could consume between 9% and 17% of total US electricity by 2030, up from roughly 4% to 5% last year. Goldman Sachs estimated in May that US data center power demand would jump from 31 gigawatts in 2025 to 66 gigawatts in 2027.
That projected surge has ignited a feeding frenzy among nuclear startups. Valar Atomics, another small modular reactor developer, was in talks this July to raise funding at a $6 billion valuation, TechCrunch reported. Aalo Atomics, building sodium-cooled microreactors, raised a $100 million Series B in August 2025 after closing a $27 million Series A the prior August. Oklo, the publicly traded fast microreactor developer, is pursuing deployment through Department of Energy and NRC licensing channels.
Apollo participated in Y Combinator's P26 batch, part of the accelerator's recent push into hard tech and climate infrastructure.
Spending the Capital
The new funding will go toward expanding demonstration work and long-duration reliability testing of reactor subsystems, Apollo said. The company also plans to build manufacturing capacity and continue regulatory engagement with the NRC. Apollo said it intends to vertically integrate key manufacturing processes and grow its engineering and operations teams, though it didn't specify headcount targets.
Whether Apollo can deliver on its aggressive deployment timeline may determine if it captures early contracts in what could become a multibillion-dollar market. For now, the company has bet its future on a redesigned steam generator and the proposition that nuclear power can be made fast, small, and factory-produced. The data center industry will be watching.
