Thorium is key to our net zero goals

Thorium is key to our net zero goals

Subject: Science and technology

Section: Nuclear Technology

Concept:

• Apart from coal, thorium is the only abundant energy source in India. Recent developments at the Bhabha Atomic Research Centre(BARC) give hope that this mineral can be India’s answer to green energy.
• BARC is working on several technologies for using thorium, of which two are noteworthy.
• One is the ‘Indian high­ temperature reactor’ (IHTR), which is designed to produce heat and, in turn, produce hydrogen through the ‘sulphur­iodine’ method.
• The other important thorium technology at BARC is the ‘Indian molten salt breeder reactor’(IMSBR). This 5­MW pilot project in Visakhapatnam is cloaked in secrecy, with BARC declining to share information about it.

High temperature nuclear reactors

• High temperature nuclear reactors (HTRs) represent a novel way to produce hydrogen at large scale with high efficiency and less carbon footprint.
• High Temperature Reactor (HTR) technology has been developed from the late 1940s in US and Germany.
• The present Very High Temperature Reactor (VHTR), operating at >7500 C, has over the years, evolved into a new reactor concept, designed to be a very efficient and safe system.
• It is a helium-gas cooled, graphite-moderated, thermal neutron spectrum reactor, which can provide electricity and process heat for wide-ranging applications, including hydrogen production.
• Hydrogen production through fossil fuels entails CO2 emissions. Therefore splitting of water to produce hydrogen is a better alternative.
• There are several methods to extract hydrogen from water and two of the highly used processes are
• High Temperature Electrolysis (HTE) and
• Thermo-chemical cycles.
• Both these processes require very high temperatures, which can be provided by the VHTRs.

Indian high­ temperature reactor

• Indian High Temperature Reactor (HTR) technology development programme is aimed at nuclear hydrogen production by splitting water.
• Indian HTR development programme has two elements:
• a 100 kW (thermal), 1,000 degrees C portable ‘compact high-temperature reactor’ (CHTR) for technology demonstration;
• a 600 MW (thermal), 1,000 degrees C ‘Indian high-temperature reactor hydrogen’, or IHTR-H.
• These two reactors would be powered by ‘TRISO-coated particle’ fuel. TRISO — ‘tristructural isotropic’ — comprises uranium, carbon and oxygen, all of which India can make.
• The IHTR-H is designed to produce about 7,000 kg of hydrogen, 18 MWhr (thermal) of energy per hour and 9 million litres of water a day.

Indian molten salt breeder reactor ( IMSBR )

• The Indian molten salt breeder reactor (IMSBR) is the platform to burn thorium as part of 3rd stage of Indian nuclear power programme.
• The fuel in IMSBR is in the form of a continuously circulating molten fluoride salt which flows through heat exchangers for ultimately transferring heat for power production to Super-critical CO2 based Brayton cycle (SCBC) so as to have larger energy conversion ratio as compared to existing power conversion cycle.
• Because of the fluid fuel, online reprocessing is possible, extracting the 233Pa (formed in conversion chain of 232Th to 233U) and allowing it to decay to 233U outside the core, thus making it possible to breed even in thermal neutron spectrum.
• Hence IMSBR can operate in self-sustaining 233U-Th fuel cycle. Additionally, being a thermal reactor, the 233U requirement is lower (as compared to fast spectrum), thus allowing higher deployment potential.
• These reactors require several new technology development which are being undertaken by BARC.
• These include 7Li enrichment, salt preparation and purification, salt characterisation and chemistry, structural material development and characterisation, nuclear grade graphite development and characterisation, component development, SCBC and reprocessing for IMSBR.
• In addition, a dedicated facility, Molten Salt Breeder Reactor Developmental Facility (MSBRDF) is being designed for full scale demonstration of all major systems for the 5 MWth IMSBR.
• BARC has also developed Ni-Mo-Cr-Ti alloy for the vessel. R&D is being undertaken for fuel salt optimisation, characterisation, salt preparation, thermal hydraulic and corrosion studies of IMSBRs.