US nuclear start-up marks mini-reactor breakthrough
An aerial view shows Constellation’s Clinton Clean Energy Center’s single nuclear reactor power plant on Jul 25, 2025, in Clinton, Illinois, US. (File photo: Getty Images via AFP)
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NEW YORK: A nuclear start-up working on mini-reactors for the United States military has announced a crucial first step in producing a model that could be deployed at bases and other strategic sites within a few years.
Antares said on Thursday (Jun 4) that it had achieved initial criticality for its Mark-0 prototype, meaning it triggered a controlled, self-sustaining fission chain reaction for producing electricity.
It said it was the first private company to achieve the breakthrough for smaller reactors, which countries are increasingly considering to supplement their shifts to low-carbon energy grids.
The Mark-0 is one of 11 microreactor projects selected by the US Energy Department as part of an initiative to bring several models to criticality by this year’s Jul 4 celebrations marking the country’s 250th anniversary.
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US Energy Secretary Chris Wright hailed an “important milestone”.
The “achievement is proof that the US still leads the world in innovation – and that America’s nuclear renaissance is well underway”, Wright wrote on X.
Antares said it conducted the test at the Idaho National Laboratory research and testing facility.
The Mark-0 does not use water to cool the reactor like most US commercial power plants, but rather liquid sodium.
That improves efficiency and avoids the risk of overpressure and steam explosions like those seen in the 1986 Chernobyl disaster.
Sodium does require specific safety measures, however, because it ignites on contact with air and explodes on contact with water.
Antares said it planned to have operational reactors ready for US military sites by September 2028.
“We went from concept to a critical reactor, safely, in less than 12 months,” Antares CEO Jordan Bramble said.
To be commercially viable, the Antares reactor, which currently has a special authorisation from the Energy Department, requires approval from the US Nuclear Regulatory Commission.
Only one reactor design, by the start-up NuScale, has been given that green light so far.
The Energy Department said it expected other companies to reach criticality by Jul 4.
Source: AFP/rl
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