The third advanced nuclear reactor authorized by the Department of Energy (DOE) went critical on June 30, meeting a deadline set by President Donald Trump in May last year, the department said in a July 1 statement.
For a nuclear reactor, criticality means it has achieved a perfectly stable state, under which nuclear power plants can generate electricity round the clock.
In May 2025, Trump signed an executive order directing the DOE to launch a pilot program to accelerate the testing of advanced reactor designs outside of national labs, setting July 4, 2026, as the deadline for at least three advanced reactor concepts to hit criticality. Unity, the demonstrator nuclear reactor developed by Deployable Energy, “successfully completed a zero-power fueled criticality demonstration at Idaho National Laboratory” on June 30, DOE said….