small-modular-reactor
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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.
Last Energy
Last Energy is a US-based developer of factory-built micro modular nuclear power plants. Its flagship PWR-20 is a 20-megawatt pressurized water reactor assembled from truck-shippable modules and delivered as a turnkey, build-own-operate service. Rather than selling reactors, Last Energy sells electricity and heat under long-term power purchase agreements, targeting data centers and energy-intensive industries that need reliable, carbon-free baseload power without financing or operating a plant themselves.