Editing Liquid Fluoride Thorium Reactor (section)

== The Freeze Plug Safety System ==

One of the most celebrated features of the LFTR design is the '''freeze plug''' (also called a drain plug or freeze valve). A small section of the drain pipe at the bottom of the reactor is kept frozen solid by active cooling — the plug is a solid plug of solidified fuel salt. If power to the cooling system is cut for any reason — accident, earthquake, operator error, or deliberate shutdown — the freeze plug melts automatically. The entire fuel salt inventory drains by gravity into a subcritical geometry in a passively cooled catch basin below the reactor. The chain reaction stops immediately and the fuel solidifies. No operator action, no power supply, and no emergency systems are required. This is often contrasted with the Three Mile Island and Fukushima accidents, which both required active cooling systems that failed.