Antares Nuclear Startup Achieves Criticality with Small Modular Reactor at Idaho National Laboratory
Antares, a nuclear energy startup, announced its test reactor at Idaho National Laboratory reached criticality, marking the first new reactor design to achieve self-sustaining nuclear reactions under the Trump administration's accelerated nuclear development push. The milestone was driven by an executive order issued roughly a year ago directing the Department of Energy to bring three reactor designs to criticality within that timeframe. The achievement is significant for the broader small modular reactor industry, though it does not yet mean the reactor is generating electricity.
Antares announced Thursday that its test reactor at Idaho National Laboratory had reached criticality, meaning the nuclear fission reactions inside became self-sustaining — a key developmental milestone. This makes it the first new reactor design to cross this threshold under the Trump administration's executive order, which directed the Department of Energy to advance three different reactor designs to criticality in just over a year. Antares' design relies on TRISO fuel, a system that embeds safety and complexity into the fuel itself rather than the reactor structure. TRISO fuel consists of tiny pellets with a uranium oxide core surrounded by layers of carbon that moderate neutron and particle energy, all encased in a hard ceramic shell engineered to withstand extreme temperatures. While criticality is a foundational step, the reactor has not yet begun generating electricity, and the broader small modular reactor sector still faces significant hurdles — only one new design has received full licensing in the US, and no instances of that design are currently planned for construction.
What's missing
It is unclear which two other reactor designs are targeted under the executive order's criticality mandate, or how close they are to meeting that benchmark. Additionally, the commercial timeline and funding sources for Antares' reactor have not been detailed in available coverage.
How coverage differed
Only one source was available for this story. Ars Technica, rated center, presented the news in a technically detailed and measured tone, noting both the significance of the milestone and its limitations, without overt promotional or critical framing.
What different sources said
- Ars TechnicaCenter
Small modular nuclear reactor reaches criticality in first test
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