Microsoft-backed US small modular reactor company Aalo Atomics has become the first developer to achieve criticality as part of the US Department of Energy’s (DOE) Reactor Pilot Program, a potential game-changer for data centers' SMR ambitions.The company reported that it had achieved criticality for its Aalo-X Critical Test Reactor in the early morning hours of July 4, 2026, at Idaho National Laboratory (INL), meeting the deadline stipulated in the program. Criticality is when a nuclear reactor achieves a self-sustaining chain reaction. The company broke ground on the test reactor in September of last year.“Reaching criticality is our most significant milestone to date, as it paves the way for the deployment of the Aalo Pod to power commercial data centers once it receives authorization from the Nuclear Regulatory Commission,” said Matt Loszak, CEO, Aalo Atomics. “More importantly, the Aalo-X Critical Test Reactor has the same full-scale core components as our commercial reactors. The Aalo-X’s 10MWe reactor design positions it as the premier power provider for the modern data center.”The company also recently announced a collaboration with Microsoft and Nvidia to develop an automated co-piloting system to improve nuclear reactor safety.The Aalo-X reactor is a precursor to the company’s flagship offering, dubbed the Aalo pod. The 50MW microreactor comprises five 10MWe reactors driving a single turbine. It is sodium and air-cooled, meaning it requires no external water source.As part of its experimental plant development, the company plans to construct a co-located data center adjacent to the reactor to demonstrate proof of concept within the sector. While plans for the data center have yet to be revealed, DCD understands that Aalo sees co-location as a key part of its model.The DOE’s Nuclear Reactor Pilot Program was launched last year. A total of 11 advanced nuclear reactor companies were selected to take part, many of which have signed deals with data center operators. In addition to Aalo, the other companies included Antares Nuclear Inc., Atomic Alchemy Inc., Deep Fission Inc., Last Energy Inc., Oklo Inc., Natura Resources LLC, Radiant Industries Inc., Terrestrial Energy Inc., and Valar Atomics Inc.SMRs and microreactors are smaller-scale nuclear power units that can be manufactured in factories and assembled on-site. They are designed to be scalable, incorporate advanced safety measures, and require less initial capital than conventional nuclear plants.Aalo is one of several advanced nuclear firms that are seeking to tap into the data center market. Last year, Equinix unveiled one of the largest deals yet, securing three separate agreements with next-generation reactor developers that could supply as much as 774 megawatts of electricity. Over the past year, other tech and cloud giants, including Amazon, Google, Data4, Oracle, Switch, and Endeavour, have also struck deals with advanced nuclear companies.