Landmark part of ambitious US federal bid to have three test units online by 4 July
US nuclear reactor company Antares announced on 4 June that its Mark-0 microreactor achieved initial criticality at Idaho National Laboratory (INL), making Antares the first private company to bring an advanced reactor to criticality under the US Department of Energy’s (DOE) push to deploy advanced plants.
The California-based company said the demonstration, backed by the DOE under its Reactor Pilot Program, meets an ambitious objective set by president Donald Trump and the DOE to reform how the federal government tests advanced reactors, and it establishes a replicable licensing pathway that the DOE and industry can use to accelerate future reactor demonstrations on commercial timelines.
“Today’s achievement is a historic moment for American nuclear energy,” said energy secretary Chris Wright.
“By bringing the first American non-light water privately developed reactor to criticality in more than four decades, Antares has shown what is possible when American innovation is unleashed.”
In April Wright said the US was on track to meet its objective of having multiple nuclear test reactors reach criticality by the country’s 250th anniversary on 4 July 2026.
When asked in an interview with the Wall Street Journal if the US would reach its target of having three reactors reach criticality by that date, Wright said: “We are going to hit that, amazingly… Let’s get those reactors running and prove that they’re real by July 4 on our 250th anniversary.
“We will have multiple small modular reactors [SMRs] running in the next three months. I am thrilled by this,” he added.
Last year the DOE launched the Reactor Pilot Program to accelerate the testing of advanced nuclear reactor designs and ensure at least three reactors reach criticality by 4 July. Criticality is the state where a nuclear chain reaction becomes self-sustaining.
The programme is designed to stimulate research and development of nuclear reactors rather than demonstrate reactors for commercial development.
The programme builds on efforts to demonstrate advanced reactors on DOE sites through microreactor testbeds and other projects led by the Department of War and private industry.
The companies selected under the programme were: Antares Nuclear, Aalo Atomics, Atomic Alchemy, Deep Fission, Last Energy, Natura Resources, Oklo, Radiant, Terrestrial and Valar Atomics.
According to Antares, the Mark-0 reactor validates key reactor physics parameters for its reactors and contributes verification and validation data back to the Department of War’s Project Pele, a US initiative to design, build and demonstrate a transportable nuclear microreactor.
Antares said Mark-0 benefited from using the same nuclear fuel as the Project Pele programme. The advanced Triso (TRi-structural ISOtropic) fuel for the plant was fabricated by Virginia-based BWXT.
Reactors For Earth, Space And Underseas
Antares is developing what it calls factory-produced, deployable fission microreactors of up to 1 MW to provide strategic energy for mission-critical systems across Earth, space and underseas.
In December Antares raised $96m (€82m) in Series B funding as it pursues its reactor design.
“Hitting our commitments is everything to us,” said Antares chief executive officer Jordan Bramble.
“Nuclear in America has been defined for too long by delays, by companies that said they would and then didn’t.
“We said criticality in 2026, electricity production in 2027, and power to the warfighter in 2028.
“Today is the first of those commitments delivered on the schedule we set.”
