India's three-stage nuclear power programme was formulated by Homi Bhabha in the 1950s to secure the country's long term energy independence, through the use of uranium and thorium reserves found in the monazite sands of coastal regions of South India. The ultimate focus of the programme is on enabling the thorium reserves of India to be utilised in meeting the country's energy requirements. This is because despite having only 1-2% of the world’s Uranium reserves, India possesses the largest Thorium reserve out of any country, with up to 33% of the entire world’s reserves. As India is the world's leader in thorium research, with no other countries having done as much neutron physics on thorium studies and according to Siegfried Hecker, a former director of the Los Alamos National Laboratory in the United States, "India has the most technically ambitious and innovative nuclear energy programme in the world. The extent and functionality of its nuclear experimental facilities are matched only by those in Russia and are far ahead of what is left in the US." As such for Stage III of the three-stage nuclear program, instead of a thermal breeder reactor, a molten salt reactor have instead been proposed as an alternate path to a functioning commercial reactor. The planned timeline is for the prototype Indian Molten Salt Reactor is to be constructed by 2028 at latest, with the first commercial 500MWe MSR to be commissioned by 2035 at latest.

Reactor Core

The Reactor core can be called a “fuel vat”. It holds fuel salt, blanket salt and moderator material (graphite control rods). The fuel and blanket salts are kept separated in two plena integrated into a single structure within the reactor vessel. Fuel salts are directed into the appropriate channels as it is circulated through the reactor. The internal graphite structures needs to be replaceable since it subjected to a fast andthermal neutron flux that is greatly in excess of that which will be experienced by the metallic reactor vessel itself. However unlike in a Uranium fueled LWR, the graphite control rods can be replaced without interrupting reactor activities. Thorium fuel is introduced as a tetrafluoride into the blanket salt mixture of the reactor. The blanket salt surrounds the active reactor core, absorbing the neutron from Thorium-232, which leads to the transmutation of the thorium-232 via nuclear beta decay, first to protactinium-233 and later to uranium-233. Both the protactinium and the uranium are chemically removed from the blanket salt mixture and introduced into the fuel salt mixture in the reactor to fission. The fission products are later chemically removed from the fuel salt. This makes the Thorium-232 reactor extremely efficient, however it requires extensive chemical treatment plants nearby for fuel processing. The reactor core is constructed from Niobium-Molybdenum-Nickel alloy to prevent fuel corrosion from the Flouride salt fuel mixture due to their chemical stability. The fluoride salt mixtures have a high heat capacity, equivalent to water, while not reacting vigorously with air or water unlike other liquid metals. The components of the fuel salt has both upsides and downsides, with the two most important are lithium-7 fluoride and beryllium fluoride. The 2 natural lithium isotopes must be separated (to be specifically Lithium-7) as Lithium-6 is far too absorptive of neutrons. Beryllium fluoride is chemically toxic but has very attractive nuclear and physical properties. The chemical processing and purification of fluoride salt mixtures typically involves using powerful reactants such as gaseous fluorine and hydrogen fluoride which are very toxic and Reactive. However the fact that the fuel salt is processed in salt form provides a safety bonus as it prevents accidental criticality, as while water is a great moderator, salt is not. Flouride salt moderates neutrons sufficiently to prevent the formation of a fast neutron system, however it is not good enough to generate a thermal neutron spectrum. As such, graphite moderator rods are also used.

Primary Loop

The Primary Loop direct the fuel salt to the primary heat exchanger, where the fuel salt transfer its heat to the coolant salt. The primary loop system begins and ends with its connection to the reactor vessel and includes the primary pump, the PHX, the bubble injection system, and the fuel salt drain tank and its associated external cooling system.

Intermediate Loop

The Intermediate Loop direct the heat from the Primary Loop to the Power Conversion System. The intermediate loop system includes the PHX, the coolant salt pump, the salt side of the gas heater (or intermediate heat exchanger, IHX), the coolant salt drain tanks, and the pressure relief (blowout) valves. The intermediate loop is also a safety feature, separating the Primary loop from the high pressure PCS. In case of PCS failure this feature prevents the high pressure from transmitting back to the Primary Loop through the coolant salt, which, being not designed for high pressure, would likely lead to rupture and dispersal of radioactive materials. In the event of a failure in the gas heater and the pressurization of the intermediate loop, the pressure relief valves allow coolant salt to leave the loop. The Intermediate Loop also serves to cool the coolant fuel salt with another coolant salt, which is far more compact than gas cooling allowing it to be smaller and reduces the fuel salt inventory of the primary loop which reduces the amount of fissile material needed for a given power rating.

Power Conversion System (PCS)

The PCS, well, converts the energy from the salt and ejects the waste materials. It uses a supercritical carbon dioxide gas turbine employing the recompression cycle. The PCS includes four heat exchangers: the gas side of the gas heater, the gas cooler, and the high-temperature and low-temperature recuperators. It also includes the main turbine, the main compressor, the recompressor, and the electrical generator. It interracts with the Intermediate Loop through the gas heater. The PCS and carbon dioxide working fluid in the cycle provides a final barrier to tritium release into the environment. Tritium generation is an inevitable consequence of using lithium and beryllium in the salt mixture and thus the PCS also includes a tritium removal system.

Chemical Proccessing System

The main function of the chemical processing system is to remove uranium and protactinium from the blanket salt and to return uranium to the fuel salt for fission. Its secondary function is to remove fission products from the fuel salt and to further process them into acceptable forms. The safety-related functions of the chemical processing system mainly involve the safe handling of highly radioactive materials. Highly reactive gaseous flourine and hydrogen is needed however. A class of fission products including selenium and tellurium will migrate with gaseous hydrogen and hydrogen fluoride and are handled in a potassium hydroxide neutralization cleanup system. Other wastes are processed in a metallic state in bismuth, and oxidized before being shipped away from the site. The small amount of waste produced from the LFTR means that the disposal process do not interfere much with operations (as the U-233 is reused).

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The LFTR would be highly competitive price wise and even when considering environmental impact, to other green energies. The IMSR prototype could start entering service in 2025, with the construction of the commercial reactors to follow suite 5 years later at most, 2 years at our best estimates. Significant development will however be needed to prepare for long term operations of the Chemical Processing System, which will be learnt through the IMSR, this is the primary factor determining the start date of the construction of the first commercial LFTR. The Department for Atomic Energy is budgeted to complete the IMSR by 2025, and after 3-5 years of operational studies the first commercial reactors should start their construction, however, this could be delayed by the relative primitiveness of India’s thorium exploitation infrastructure. Additional infrastructural fundings to be allocated under Rural Development until 2030 are to be budgeted for the development of 17 monazite mines for an approximated capacity to process up to 500 tons of Thorium a year to allow for a 2030 service date for the first commercial powerplants.

Credit: Most of the information are from the IAEA, with a few tweaks to suite the circumstance