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.