Thorium is a chemical element with the symbol Th and atomic number 90. It is a naturally occurring, slightly radioactive metal. Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust. Thorium was successfully used as an alternative nuclear fuel to uranium in the molten-salt reactor experiment (MSR) from 1964-1969 to produce thermal energy, as well as in several light-water reactors using Th232-U233 fuel including Shippingport, Pennsylvania (operation commenced 1977, decommissioned in 1982). Currently, officials in the Republic of India are advocating a thorium-based nuclear program, and a seed-and-blanket fuel utilizing thorium is undergoing irradiation testing at the Kurchatov Institute in Moscow. Advocates of the use of thorium as the fuel source for nuclear reactor state that they can be built to operate significantly cleaner than uranium based power plants as the waste products are much easier to handle.
Thorium does not require enrichment to be used as a nuclear fuel. Almost all Thorium that is available on Earth exists in the form of the desired Thorium232 isotope, i.e. only chemical separation is needed to obtain the fuel. This is to be compared with Uranium, where a costly and complicated enrichment process has to be undertaken (in addition to chemical separation) to increase the content of U235 in the bulk of Uranium from the natural value of 0.7% to higher levels, for Uranium to be used as a nuclear fuel.
Thorium is much more abundant in Earth's crust than Uranium. There is about four times more of Thorium than Uranium in the Earth's crust.
Switching nuclear infrastructure from Uranium to Thorium is hard."Is Thorium an Energy Alchemist's Dream?" Scitizen. Mar 27th, 2009: "with all these advantages, what is holding back development of thorium-based fuels? First, most commercial reactors run on uranium. Thorium fuels have been used in some commercial reactors with success. But no fuel-producing infrastructure yet exists for supplying thorium commercially, and so it remains for more economical and reliable to use uranium. (One small company has been trying to change that with limited success.)"
LFTR reactor can be operated continuously. LFTR reactor can be refueled while in operation, so it can (in principle) generate electricity continuously.
LFTR reactor operates at high temperatures. LFTR reactor operates at temperatures higher than than "classical" Uranium PWRs (Pressurized Water Reactors). This translates to higher possible thermodynamic efficiency of the process of conversion of thermal to electrical energy (up to around 50%, compared to around 30% in the case of Uranium PWRs). Since less waste heat is produced, there are lower demands on the cooling system, i.e. the cooling towers can be smaller (compared to PWRs with equal power). Higher operating temperatures also offer the possibility of using gas turbines instead of steam turbines, possibly simplifying the non-nuclear part of LFTR based power plant.
LFTR reactor operates at low pressures. Unlike PWR, LFTRs operate at low pressure, which is favorable because of lower mechanical loads on reactor vessel and other parts of the machinery, hence lowering the risk of accident. It also decreases the size of containment building required to enclose the reactor.
Nuclear waste produced by LFTR is relatively short-lived. The fission products of LFTR reactor are much more favorable than those of PWR. 83% of the fission products becomes stable (non-radioactive) within 10 years. The remaining 17% need to be isolated (only) for another 300 years. This alleviates the need for building large and costly "permanent" storage facilities, such as the one in Yucca Mountain.
LFTR produces much less nuclear waste than PWR. LFTR uses up (i.e. breeds and fissions) up to 100% of the fuel. In solid-fuels based PWR the achievable burn-up of fuel is limited (among other things) by the accumulation of fission products inside fuel rods, changing both their mechanical properties (leading to deformation such as swelling) and reactivity ("neutron poisoning" of the fuel rods). In the case of a reactor based on liquid fuel (such as LFTR), the fuel can be continuously reprocessed, and LFTR is therefore able to utilize (in the ideal case) all the fuel fed into it, producing much less waste per generated joule than PWR.
LFTR has the potential to utilize existing nuclear waste as a fuel.
LFTR reactors can be designed to be self-regulating. No control rods are required, nor operator input. When the load is too small, less heat can be removed through the heat exchanger. This causes more heat to be build up in the core, resulting in the hotter liquid fuel expanding out of the reactor core, reducing the reaction. In times of greater load, the reverse process happens.
Molten fluoride salts are highly reactive. Molten fluoride salts, proposed as a solvent/primary coolant/heat transfer agent in LFTR reactors are highly reactive to many solids (e.g. corrosive to many metals), especially when heated to high temperature inside a working reactor . This puts high demands on and severely limits the choice of materials used for the reactor vessel, plumbing and other parts of the machinery, bringing many difficulties and intricacies along.
Reprocessing Uranium-233 to make Thorium is challenging."Is Thorium an Energy Alchemist's Dream?" Scitizen. Mar 27th, 2009: "the advantages of thorium come from the reprocessing and extraction of the uranium-233 produced by breeding. This reprocessing has proven challenging because of the highly radioactive byproducts produced during breeding and the resulting high costs associated with processing fuel and building fuel assemblies."
Thorium waste is less radioactive than Uranium."Is Thorium an Energy Alchemist's Dream?" Scitizen. Mar 27th, 2009: "the danger from the waste of the thorium fuel cycle is potentially far less long-lived. The claim is that the reprocessed waste will be no more radioactive than thorium ore after about 300 years. This claim is based on the idea that virtually all of the long-lived radioactive products of breeding will be consumed in the reactor before the final round of reprocessing takes place."
Making nuclear bombs with Thorium is harder than with Uranium. While it is possible to build a bomb from U233, the fissile isotope in a Thorium reactor, it's not very easy to do. This is because the gamma radiation is much higher than with U235, making material handling much more challenging. There is less chance, therefore, of weapons diversion.