Thorium and Molten Salt Reactors in China and Elsewhere

China is finishing the 2 megawatt prototype Thorium Molten Salt Reactor (TMSR-LF1), in Wuwei, a desert city in Gansu province.
Construction work on the TMSR is due to finish in August and a test run of equipment could start as early as September.

Molten salt and thorium reactors are inherently safer and can have less nuclear waste (aka unused nuclear fuel.) Nuclear fuel is unused because even numbered isotopes are harder to split or react. Fast reactors have neutrons moving at higher speeds (one hundred times faster) needed to cause uranium 238 to react into plutonium.

Oak Ridge National Laboratory (ORNL) in the United States operated an experimental 7.34 MW (th) MSR from 1965 to 1969, in a trial known as the Molten-Salt Reactor Experiment (MSRE). This demonstrated the feasibility of liquid-fuelled reactors cooled by molten salts.

China has been developing waterless nuclear reactors. Construction work on the first commercial molten salt reactor should be completed by 2030. This will allow the construction of such nuclear reactors even in desert regions and in the plains of central and western China. The molten salt reactor will be powered by liquid thorium instead of uranium.

SINAP has two streams of TMSR development – solid fuel (TRISO in pebbles or prisms/blocks) with once-through fuel cycle, and liquid fuel (dissolved in fluoride coolant) with reprocessing and recycle. A third stream of fast reactors to consume actinides from LWRs is planned. The aim is to develop both the thorium fuel cycle and non-electrical applications in a 20-30 year timeframe.

*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. It is optimized for high-temperature based hybrid nuclear energy applications. SINAP aimed at a 2 MW pilot plant initially, though this has been superseded by a simulator (TMSR-SF0). A 100 MWt demonstration pebble bed plant (TMSR-SF2) with open fuel cycle is planned by about 2025. 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. It is optimized for utilization of thorium with electrometallurgical pyroprocessing.

*SINAP aims for a 2 MWt pilot plant (TMSR-LF1) initially, then a 10 MWt experimental reactor (TMSR-LF2) by 2025, and a 100 MWt demonstration plant (TMSR-LF3) with full electrometallurgical reprocessing by about 2035, followed by 1 a GW demonstration plant. The TMSR-LF timeline is about ten years behind the SF one.

A TMSFR-LF fast reactor optimized for burning minor actinides is to follow.

The TMSR-SF0 is one-third scale and has a 370 kW electric heat source with FLiNaK primary coolant at 650°C and FLiNaK secondary coolant.

The 10 MWt TMSR-SF1 has 17% enriched TRISO fuel in 60mm pebbles, similar to HTR-PM fuel, and coolant at 630°C and low pressure. Primary coolant is FLiBe (with 99.99% Li-7) and secondary coolant is FLiNaK. Core height is 3 m, diameter 2.85 m, in a 7.8 m high and 3 m diameter pressure vessel. Residual heat removal is passive, by cavity cooling. A 20-year operating life was envisaged but the project is discontinued.

The 2 MWt TMSR-LF1 is under construction at Wu Wei in Gansu in a $3.3 billion programme. It will use fuel enriched to under 20% U-235, have a thorium inventory of about 50 kg and conversion ratio of about 0.1. FLiBe with 99.95% Li-7 would be used, and fuel as UF4. The project would start on a batch basis with some online refueling and removal of gaseous fission products, but discharging all fuel salt after 5-8 years for reprocessing and separation of fission products and minor actinides for storage. It would proceed to a continuous process of recycling salt, uranium and thorium, with online separation of fission products and minor actinides. It would work up from about 20% thorium fission to about 80%.

Beyond these, a 373 MWt/168 MWe liquid-fuel MSR small modular reactor is planned, with supercritical CO2 cycle in a tertiary loop at 23 MPa using Brayton cycle, after a radioactive isolation secondary loop. Various applications as well as electricity generation are envisaged. It would be loaded with 15.7 tonnes of thorium and 2.1 tonnes of uranium (19.75% enriched), with one kilogram of uranium added daily, and have 330 GWd/t burn-up with 30% of energy from thorium. Online refueling would enable eight years of operation before shutdown, with the graphite moderator needing attention

SOURCES- World nuclear news, SCMP, CEA, ESFR Smart
Written By Brian Wang,

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