The U.S. Idaho National Laboratory has successfully completed the first fueled experiment at the Transient Reactor Test (TREAT) Facility. TREAT is one of the remaining U.S. research reactors that use HEU fuel. It was placed on standby in 1994, but recently resumed operations. The facility will be used for "the development of nuclear fuels, for both the existing fleet and a new generation of advanced reactors under design."
The decision to restart the reactor was made in 2014. The Department of Energy studied the possibility of converting the reactor to LEU, but decided against it. TREAT uses about 20 kg of HEU enriched to 93.1%.