Facility will be used to achieve pilot first criticality by 4 July deadline
US-based advanced reactor developer Aalo Atomics has completed construction of its critical test reactor at Idaho National Laboratory, the company announced at an onsite ceremony.
The company said the 10-MW sodium-cooled experimental reactor, known as Aalo-X, is designed to validate its technology at full scale ahead of future commercial deployment.
The test facility will be used to achieve pilot first criticality, the point at which a self-sustaining nuclear chain reaction is established. The company broke ground for the project in September 2025.
Aalo has previously said the facility is the first step towards a planned line of “extra-modular reactors” (XMRs), which it said is a new category of modular reactor designed to bridge the gap between microreactors and small modular reactors (SMRs).
Aalo said it expects the reactor to reach criticality before 4 July 2026, in line with targets under the US Department of Energy’s (DOE) nuclear reactor pilot programme.
According to Aalo, the reactor was manufactured at the company’s facility in Austin, Texas, before being transported and installed at the Idaho site.
The installation includes the reactor vessel, control and instrumentation systems, shielding and control room infrastructure.
The project is one of several advanced reactor demonstrations supported by the Department of Energy (DOE), which aims to accelerate testing and deployment of new nuclear technologies in the US.
Aalo said the test reactor is a precursor to its planned Aalo Pod system.
The company said earlier the Aalo Pod design is based on pods containing five factory-built, 10-MW Aalo-1 XMRs arranged around a single turbine to produce 50 MW. According to Aalo, each Aalo-1 reactor uses liquid sodium metal coolant, which allows for higher energy density than conventional water-cooled reactors.
Final approval from the DOE is still required before the reactor can begin operation. Since the project is at a federal government site, permitting and regulatory supervision is carried out by the DOE.
Aalo’s chief executive Matt Loszak said nuclear fuel for the test reactor at INL “will be arriving any day now.”
