The Liquid Fluoride Thorium Reactor is a type of Molten Salt Reactor. Molten Salt Reactors are Generation IV nuclear fission reactors that use molten salt as either the primary reactor coolant or as the fuel itself; they trace their origin to a series of experiments directed by Alvin Weinberg at Oak Ridge National Laboratory in the ‘50s and ‘60s. The LFTR is differentiated from other variants of the MSR by the fact that it runs on thorium rather than uranium, thorium being an element that is fertile rather than fissile, and which will transmute to fissile uranium-233 upon exposure to neutrons.
In 2011 the Chinese Academy of Sciences announced plans to commercialize a thorium-based MSR in 20 years (it is also developing non-thorium MSRs and solid fuel thorium reactors). The Shanghai Institute of Applied Physics has since employed 700 nuclear engineers for this project. The plan is for a 10MW pilot LFTR is expected to be operationalized in 2025, with a 100MW version set to follow in 2035.
China theoretically has enough thorium to supply all its energy for the next 20,000 years.
Shanghai Institute of Applied Physics (SINAP, under the Academy) has two streams of TMSR development – solid fuel (TRISO in pebbles or prisms/blocks) with once-through fuel cycle, and liquid fuel (dissolved in FLiBe coolant) with reprocessing and recycle. A third stream of fast reactors to consume actinides from LWRs is planned.
The TMSR-SF stream has only partial utilization of thorium, relying on some breeding as with U-238, and needing fissile uranium input as well. SINAP aims at a 2 MW pilot plant (TMSR-SF1) initially, and a 100 MWt experimental pebble bed plant (TMSR-SF2) with open fuel cycle by about 2025, then a 1 GW demonstration plant (TMSR-SF3) by 2030. TRISO particles will be with both low-enriched uranium and thorium, separately.
The TMSR-LF stream claims full closed Th-U fuel cycle with breeding of U-233 and much better sustainability with thorium but greater technical difficulty. SINAP aims for a 2 MWt pilot plant (TMSR-LF1) by 2018, a 10 MWt experimental reactor (TMSR-LF2) by 2025 and a 100 MWt demonstration plant (TMSR-LF3) with full electrometallurgical reprocessing by 2035, followed by 1 a GW demonstration plant. A TMSFR-LF fast reactor optimized for burning minor actinides is to follow.
SINAP sees molten salt fuel being superior to the TRISO fuel in effectively unlimited burn-up, less waste, and lower fabricating cost, but achieving lower temperatures (600°C+) than the TRISO fuel reactors (1200°C+). Near-term goals include preparing nuclear-grade ThF4 and ThO2 and testing them in a MSR. The US Department of Energy is collaborating with the China Academy of Sciences on the program, which had a start-up budget of $350 million. The target date for TMSR commercial deployment is 2032.
According to Flibe Energy, headed by nuclear scientist Kirk Sorensen, thorium is so energy dense that 6600 tonnes of it could replace the ‘combined 5.3 billion tonnes of coal, 31.1 billion barrels of oil, 2.92 trillion cubic meters of natural gas, and 65,000 tonnes of uranium that the world consumes annually’. It is approximately 3X more abundant in the Earth’s crust than uranium, and significant quantities have already been extracted as the by-products of existing mining operations. Most compellingly, the energy output of a LFTR, per metric ton of thorium ore, is estimated to be 200X greater than the output of a Light Water Reactor (a type of PWR).
Flibe Energy in the USA is studying a 40 MW two-fluid graphite-moderated thermal reactor concept based on the 1970s MSRE. It uses lithium fluoride/beryllium fluoride (FLiBe) salt as its primary coolant in both circuits. This is based on earlier US work on the molten salt reactor program. Fuel is uranium-233 bred from thorium in FLiBe blanket salt. Fuel salt circulates through graphite logs. Secondary loop coolant salt is sodium-beryllium fluoride (BeF2-NaF). A 2 MWt pilot plant is envisaged, and eventually 2225 MWt commercial plants.
SOURCES – Adam smith, Flibe Energy, World Nuclear Association, youtube