Antares, a nuclear start-up, has announced a significant advancement in its development of mini-reactors for the US military, achieving initial criticality for its Mark-0 prototype. This milestone indicates that the reactor has successfully initiated a controlled, self-sustaining fission chain reaction, a crucial step toward producing electricity. The Mark-0 is part of a broader initiative by the US Energy Department, which aims to have several microreactor models reach criticality by July 4, coinciding with the nation's 250th anniversary. Unlike traditional reactors, the Mark-0 employs liquid sodium for cooling, which improves efficiency and mitigates risks associated with overpressure and steam explosions. However, sodium's reactive nature necessitates stringent safety measures. Antares plans to deploy operational reactors at military sites by September 2028. US Energy Secretary Chris Wright praised this achievement as evidence of America's ongoing nuclear renaissance and innovation leadership. For commercial viability, Antares must secure approval from the US Nuclear Regulatory Commission, which has thus far only approved one other reactor design.