How Thorium Reactors Work
The isotope of thorium that’s being studied for power is called Th-232, comes from rocks in the ground.
- Th-232 + n -> Th-233: Th-232 is placed in a reactor, where it is bombarded with a beam of neutrons. In accepting a neutron from the beam, Th-232 becomes Th-233, but this heavier isotope doesn't last very long.
- The Th-233 decays to protactinium-233,
- which further decays into U-233. The U-233 remains in the reactor and, similar to current nuclear power plants, the fission of the uranium generates intense heat that can be converted to electricity.
To keep the process going, the U-233 must be created continuously by keeping the neutron-generating accelerator turned on. So, A thorium fuel cycle, can be immediately shut down by turning off the supply of neutrons. Shutting down the fuel cycle means preventing the breeding of Th-232 into U-233. This doesn't stop the heating in the reactor immediately, but it stops it from getting worse.
Moreover, the thorium reactors can be designed to operate in a liquid state, where, a thorium reactor design called LFTR features a plug at the bottom of the reactor that will melt if the temperature of the reacting fuel climbs too high. If that happens the hot liquid would all drain out and the reaction would stop.
Thorium would be easier to obtain than uranium. While uranium mines are enclosed underground and thus very dangerous for the miners, thorium is taken from open pits, and is estimated to be roughly three times as abundant as uranium in the Earth’s crust.
http://blogs.discovermagazine.com/crux/2015/01/16/thorium-future-nuclear-energy/#5465
http://www.theguardian.com/environment/2011/nov/01/india-thorium-nuclear-plant
http://articles.economictimes.indiatimes.com/2014-08-07/news/52556083_1_thorium-rich-kalapakkam-generation
http://liquidfluoridethoriumreactor.glerner.com/
What is a Liquid Fluoride Thorium Reactor?
A type of Molten Salt Reactor, completely different reactor than Light Water Reactor (LWR), with molten fuel cooled by stable salts. A LFTR can use inexpensive Thorium (would become uranium inside the reactor). Slightly different type of MSR can consume the uranium/plutonium waste from solid fueled reactors as fuel. MSRs make no long-term nuclear waste.
Safer
- LFTRs have no high pressure to contain (no water coolant), generate no combustible or explosive materials;
- Freeze Plug melts in emergency, fuel drains to passive cooling tanks where fission is impossible;
- Reactor materials won’t melt under normal or emergency conditions, radioactive materials stay contained. (Even if a bomb or projectile breaks the reactor vessel, it makes a spill that cools to solid, doesn't interact with air or water, with most fission products chemically bonded to the salt);
- LFTRs can passively cool even without electricity (never uses water);
- Salt coolant can’t boil away (boiling point much higher than reactor temperature), so loss of coolant accidents are physically impossible.
Much Less Nuclear Waste
LWR uses ~2% of the fuel, because fission products trapped in the fuel pellets block fission. The rest of the uranium is considered “waste”, to be stored for over 100,000 years.
MSR has molten fuel, no fuel pellets, no fuel rods. Some of the fission products, that block fission best, are gasses — in LWR they are carefully trapped in the pellets, in MSR they bubble right out of the fuel salt and are collected. Most other fission products are easily chemically separated from the circulating fuel salt. Most MSR designs, including LFTR, use over 99% of the fuel.
A LFTR’s waste is safe within 350 years. To produce 1 gigawatt electricity for a year, takes 800kg to 1000kg of thorium or uranium/plutonium waste.
