An illustration of a reactor core (L), earlier this year PM Modi is seen inspecting a nuclear facility

India's Bhabha Atomic Research Centre (BARC) is currently developing a 555 MW Molten Salt Breeder Reactor (MSBR), a highly complex next-generation nuclear reactor type known for its advanced technology.

The MSBR utilises molten salt as both fuel and coolant, where fissile and fertile materials (like thorium and uranium) are dissolved in the fluoride salt mixture.

This innovative design allows for continuous circulation of the fuel within the reactor, enabling online reprocessing and breeding of fissile material, particularly uranium-233 from thorium, thus supporting a self-sustaining 233U-Th fuel cycle in the thermal neutron spectrum.

The Indian Molten Salt Breeder Reactor (IMSBR) is an integral part of India's three-stage nuclear power program aimed at exploiting the country's abundant thorium reserves.

The primary fuel salt mixture includes lithium fluoride, calcium fluoride, thorium tetrafluoride, and uranium tetrafluoride, while a secondary coolant salt of a eutectic mixture of lithium, sodium, and potassium fluorides is employed. This reactor design integrates a super-critical CO2 Brayton cycle for enhanced energy conversion efficiency compared to conventional power cycles.

BARC is engaged in developing several critical technologies essential for MSBR operation, including lithium-7 isotope enrichment, salt preparation and purification, structural materials capable of withstanding corrosive salt environments, nuclear-grade graphite development, and component fabrication.

A dedicated Molten Salt Breeder Reactor Development Facility (MSBRDF) is being set up at Visakhapatnam for full-scale demonstration of the reactor’s major systems based on a smaller 5 MW thermal prototype.

The fluid fuel nature permits removal and decay of protactinium-233 outside the core, enhancing breeding efficiency even in a thermal neutron spectrum, which reduces the need for enriched uranium compared to fast reactors and increases deployment potential. This reactor design, being a thermal breeder, offers proliferation resistance and alignment with global nuclear security objectives.

Internationally, molten salt breeder reactors have been developed only by the US in the 1960s-70s and currently China, which has operational thorium-fuelled MSRs and has achieved continuous online refuelling without shutdown. The Indian program, while following foundational research done at Oak Ridge National Laboratory (ORNL), aims to bring this complex technology indigenously to maturity, emphasising thorium utilisation and sustainable nuclear energy production.

Further R&D efforts at BARC include thermal hydraulics, corrosion studies, salt chemistry, and development of nickel-molybdenum-chromium-titanium alloys for reactor vessels. Alongside IMSBR, BARC is also developing a Molten Salt Cooled High Temperature Reactor for process heat applications like hydrogen production, highlighting the wider application scope of molten salt technologies in India's nuclear future.

IDN (With Agency Inputs)