goingcritical:aalo-xUnited States · Microreactor

Aalo-X

Developer: Aalo Atomics

Site: Idaho National Laboratory (adjacent to Materials and Fuels Complex), Idaho Falls, Idaho

Status: Critical since July 4, 2026 critical

Summary:

Fourth DOE-authorized reactor to reach criticality (zero-power fueled criticality at 12:20 a.m. MT, July 4, 2026), meeting the EO 14301 Independence Day goal

Details

DesignSodium-cooled, LEU uranium-dioxide-fueled experimental reactor (XMR / Critical Test Reactor for the 10-MWe Aalo-1)
Capacity10 MW (thermal where reported)

Milestone history

  1. Announced August 12, 2025
  2. Construction start August 2025
  3. Fuel load —
  4. First criticality July 4, 2026

References

  1. Aalo Atomics, Aalo achieves first criticality (July 4, 2026)
  2. POWER Magazine, Aalo test reactor reaches criticality at INL
  3. World Nuclear News, criticality for fourth US microreactor meets deadline
  4. Aalo Atomics via Business Wire, first to break ground in Reactor Pilot Program (Aug 28, 2025)
  5. DOE, initial Reactor Pilot Program selections (Aug 12, 2025)