# Apollo Atomics

> Apollo Atomics is a Cambridge, Massachusetts nuclear startup building the most power-dense pressurized water reactor. By redesigning the steam generator - the bulkiest part of a conventional plant - into a proprietary Compact Steam Generator, the company shrinks a proven reactor design by roughly an order of magnitude, turning a decade-long construction project into a factory-built machine that fits on a truck and deploys in under 24 months. Founded by MIT nuclear PhD Assil Halimi and operator Drew Walker, Apollo is in Y Combinator's Spring 2026 batch and is testing its design in collaboration with MIT.

- **Founded:** 2025
- **Headquarters:** Cambridge, Massachusetts, United States
- **Founders:** Assil Halimi (Co-Founder & CEO), Drew Walker (Co-Founder & COO)
- **Team size:** 2 (founders)
- **Products:** Compact Steam Generator (CSG), A-10 Reactor, A-50 Reactor, A-300 Reactor, 1 MW Demonstrator
- **Notable:** In Y Combinator's Spring 2026 (P26) batch, Reported reaching criticality with fuel ahead of a self-set July 4th target, Announced a research collaboration with MIT's Department of Nuclear Science and Engineering (April 2026)

## Products & services

- **Compact Steam Generator (CSG)** — Apollo's core innovation: a redesigned steam generator roughly 20x smaller than conventional units, shrinking the overall plant by an order of magnitude while preserving thermal output.
- **A-10 Reactor** — A ~10 megawatt-electric compact pressurized water reactor targeted at early commercial deployments and industrial sites.
- **A-50 Reactor** — A ~50 megawatt-electric reactor for larger industrial and data center loads.
- **A-300 Reactor** — A ~300 megawatt-electric reactor aimed at utility-scale, grid-connected power.
- **1 MW Demonstrator** — A first-of-a-kind demonstration reactor planned to validate the compact architecture on real hardware.

## Achievements

- In Y Combinator's Spring 2026 (P26) batch
- Reported reaching criticality with fuel ahead of a self-set July 4th target
- Announced a research collaboration with MIT's Department of Nuclear Science and Engineering (April 2026)
- Reports 20 GW in signed letters of intent
- Submitted a regulatory engagement plan to the U.S. Nuclear Regulatory Commission in early 2026
- Built on a stated 15,000+ reactor-years of commercial PWR operating experience and 15+ years of MIT research

## Latest updates

- **2026-04** — Announced research collaboration with MIT's Department of Nuclear Science and Engineering to run two-loop experimental tests of its compact PWR.
- **2026-03** — Joined Y Combinator's Spring 2026 batch; reported seed funding.
- **2026-01** — Submitted a regulatory engagement plan to the U.S. Nuclear Regulatory Commission.

## Links

- Website: https://apolloatomics.com
- LinkedIn: https://www.linkedin.com/company/apollo-atomics
- Twitter/X: https://x.com/ApolloAtomics

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Profile page: https://yespress.io/apollo-atomics-yc-p26
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Last updated: 2026-07-31