Small Nuclear Reactor Reaches Criticality in First US Test

First successful test of small modular reactor technology could reshape US energy landscape

The Morning Brief Desk · Sunday, June 7, 2026 · Updated June 18, 2026 · How the Brief is made

A small modular nuclear reactor achieved criticality for the first time in the US. The test represents a major step forward for cleaner energy deployment. The reactor, developed by startup Antares, successfully sustained a controlled nuclear chain reaction during testing this week, though it’s not yet ready to generate electricity for the grid.

Small modular reactors are designed to be cheaper and faster to build than traditional nuclear plants, with standardized components that could be manufactured in factories. The successful test brings the technology closer to commercial deployment, though significant regulatory and engineering hurdles remain before these reactors can power homes and businesses.

Sources

Ars Technica
Small modular nuclear reactor reaches criticality in first test
The reactor, from a startup called Antares, isn’t ready to generate power yet.
Science Daily
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