Valar Atomics just did something no venture-backed nuclear startup has done before. Its Ward 250 microreactor reached criticality on March 31, 2026, achieving a self-sustaining nuclear chain reaction in what amounts to the first full-scale reactor to hit that benchmark under the US Department of Energy’s accelerated pilot program.
In English: the reactor can now sustain a nuclear chain reaction on its own, which is the foundational step before a reactor can actually generate power. Think of it as the nuclear equivalent of an engine turning over for the first time. Everything before this was theory and testing. Now it’s real.
From stealth to criticality in record time
The timeline here is genuinely staggering. Valar Atomics emerged from stealth in early 2025 under CEO Isaiah Taylor. The company broke ground on the Ward 250 project on September 17, 2025, after completing a non-nuclear prototype called Ward Zero in February of that year.
By November 17, 2025, Valar had validated its core physics models through a cold criticality test of a subscale NOVA Core model at Los Alamos National Laboratory. That test essentially proved the math worked. The March 31 milestone proved the hardware works too.
