Thorium molten salt reactors (TMSRs or LFTRs) dissolve thorium (and usually some starter fissile material) in a circulating liquid fluoride salt that serves as both fuel and coolant. They operate at high temperature (~600–700 °C) but near atmospheric pressure. Main Benefits
- Fuel abundance and efficiency: Thorium is 3–4 times more abundant in Earth’s crust than uranium. Nearly all natural thorium (Th-232) can be converted into usable fuel, whereas only ~0.7% of natural uranium is fissile (U-235). One tonne of thorium can theoretically produce energy equivalent to tens of tonnes of enriched uranium (or millions of tonnes of coal) under high burn-up conditions.
- Reduced long-lived waste: The thorium cycle produces far fewer long-lived transuranics (e.g., plutonium) than conventional uranium reactors—often cited as 20× less or more, with overall transuranic waste potentially reduced by orders of magnitude when combined with recycling. Most fission products decay to low radiotoxicity in a few hundred years rather than tens of thousands. Liquid fuel enables higher burn-up and continuous removal of poisons.
- Passive safety features:
- Low-pressure operation eliminates the risk of high-pressure steam explosions and hydrogen generation common in water-cooled reactors.
- Strong negative temperature coefficient of reactivity (fuel expands when hot, reducing neutron economy and slowing the reaction).
- Freeze-plug / drain-tank design: if the system overheats, a frozen salt plug melts and the fuel drains by gravity into passively cooled subcritical tanks, stopping the chain reaction.
- High thermal efficiency and process heat: High operating temperatures support electricity generation efficiencies of ~45% (higher with advanced cycles) versus ~33% for typical light-water reactors. The heat can also support industrial uses such as hydrogen production.
- Continuous operation and fuel flexibility: Liquid fuel allows online addition of thorium and removal of fission products without shutdowns. Designs can also burn existing plutonium or other actinides.
- Proliferation resistance (relative): Bred uranium-233 is typically contaminated with uranium-232, whose decay products emit strong gamma radiation, complicating handling for weapons. Transuranic production is low. (Caveat: some reprocessing schemes that separate protactinium-233 could theoretically yield higher-purity material; denatured designs reduce this risk.)
