These Reactors Solve The Nuclear Safety Problem

TL;DR

Subcritical reactors eliminate runaway nuclear reactions by using an external neutron beam — switch it off, and fission stops immediately.

Key Points

• 1.Traditional fission reactors risk runaway chain reactions because they operate at or above criticality. Neutrons split nuclei, releasing more neutrons exponentially; moderating materials slow this but can fail, causing core meltdowns.
• 2.Subcritical reactors solve this by never reaching the criticality threshold. An external neutron beam drives fission; shutting off the beam halts the reaction instantly, making runaway scenarios physically impossible.
• 3.US startup Ampera is the most prominent subcritical company, proposing a truck-sized 15–30 MW microreactor using thorium and a claimed 'hybrid fission-fusion' neutron source. The presenter is skeptical of the fusion claim and advises against investing; SubCritical Systems (Austin) and Muon Inc are building proton-accelerator-based alternatives targeting 50–100 MW by 2028.
• 4.Subcritical reactors can also burn existing radioactive waste while generating power. Swiss company Transmutex specializes in this, and government projects in Belgium, China, and Japan are pursuing similar technology, though the presenter doubts these reactors will be cheap or compact.