Apollo Atomics aims to cut nuclear power costs by shrinking the steam generator
US startup Apollo Atomics has developed a compact steam generator that lets it build a nuclear reactor 40 times smaller than those using conventional designs, aiming to lower the cost of nuclear power. The company recently raised a $26 million seed round to build a demonstration reactor.
The nuclear power sector has seen a wave of new startups raising funding to build advanced reactors, but current projections suggest these designs are unlikely to become cost-competitive anytime soon. Apollo Atomics founders Assil Halimi and Drew Walker argue that competitors have been focused on the wrong part of the problem — not the reactor itself, but the steam generator.
A smaller part, a smaller reactor
The steam generator converts heat from the reactor's coolant loop into steam that drives a turbine. These components are typically hand-built and several stories tall, but Apollo Atomics has developed a version roughly the size of a person that can be mass-manufactured. This has allowed the company to build a reactor 40 times smaller than one using a conventional steam generator.
In the new design, both fluid loops — the coolant and the water used to generate steam — run through a compact block of metal threaded with needle-thin channels, enabling more efficient heat transfer. Halimi noted that older steam generator designs borrow heavily from coal and natural gas plants, even though those fuels have far lower energy density than nuclear fuel, meaning existing generators fail to make full use of uranium's potential.
Manufacturing and plans
Apollo Atomics plans to assemble the reactor and steam generator in a factory rather than on-site, unlike most of the industry today. Halimi estimates this will allow the company to build a 300-megawatt power plant in under 24 months, with the reactor itself costing four to five times less to produce than existing designs. The company projects electricity costs of around 3 cents per kilowatt-hour, with a goal of beating natural gas on price.
Apollo Atomics has already built a small 40-kilowatt reactor at MIT, whose research underpins the design. It plans to offer three reactor sizes, ranging from 10 to 300 megawatts. To build a demonstration reactor ahead of a planned 2028 commercial launch, the company raised a $26 million seed round, including $5 million in debt. The round was led by FCVC, with participation from several other investors, including Y Combinator, whose Spring 2026 batch included Apollo.
