US-based Deployable Energy’s demonstration reactor, Unity, has successfully achieved first criticality, marking the fulfillment of US president Donald Trump’s executive order that three advanced reactors achieve criticality by 4 July.

The Department of Energy (DOE) said Unity completed a zero-power fuelled criticality demonstration at Idaho National Laboratory (INL) late on 31 June. It is the third DOE-authorised advanced reactor to go critical by the 4 July deadline set by Trump in his May 2025 executive order.

Also in June, Antares Nuclear’s Mark-0 and Valar Atomics’ Ward 250 reactors achieved criticality, making the US the first country in history to achieve criticality in three unique advanced microreactor designs in a single month, the DOE said.