El Segundo, Calif.–based start-up Valar Atomics has taken its Ward 250 test reactor critical at the Utah San Rafael Energy Lab (USREL), becoming the second company in the Department of Energy's Reactor Pilot Program to reach the milestone, and, according to the DOE, the first to do so outside a national laboratory.

The DOE celebrated the achievement in a June 18 announcement, describing it as a "zero-power fueled criticality demonstration." The news follows a similar update for Antares Nuclear's Mark-0 reactor, which the DOE said achieved criticality at Idaho National Laboratory earlier this month.