Author – Smuruthi Kesavan
Nuclear power is undoubtedly the most controversial energy source ever used by mankind. A nuclear reactor can be a blessing and a curse, since the toxic waste disposal is its biggest problem. There is no suitable method for storing radioactive wastes, which can be in the form of solids, liquids or gases. At any point of time, their radioactivity is likely to get leached into the biosphere. Nuclear radiation can lead to severe biological effects such as genetic mutation, cancer, radiation burns etc. Considering these problems faced by nuclear reactors that use uranium and other sources, India has decided to experiment with the world’s first thorium reactor under its nuclear energy program.
Thorium is a silvery white, heavy metallic element that gets its name from ‘Thor’, the Scandinavian god of war. Thorium and uranium are the only two significantly radioactive elements that occur in large quantities in nature. Thorium is 200 times denser than uranium and is a safer alternative since it is much less radioactive than Uranium, and does not have any sort of nuclear fallout. Thorium is predicted to replace uranium as a feasible fuel in nuclear reactors, but that technology is still nascent.
The current emphasis on thorium reactor technology in India has many reasons:
- Thorium reactors produce far less waste than Uranium reactors. They have the ability to burn up most of the highly radioactive and long-lasting minor actinides that makes nuclear waste a nuisance to deal with.
- The minuscule nuclear waste that is generated is toxic for only 300-400 years rather than thousands of years.
- They are cheaper because they have higher burn-up.
- They are significantly more proliferation-resistant than present reactors.
- Finally, India has the world’s largest reserves of Thorium mineral, Monazite. India has 25% of the thorium reserves in the world, which is present in the form of monazite sand that is widespread across the coastal areas in south India.
Thorium Reactor Design
Way back in 1954, Homi Bhabha had envisioned India’s nuclear power program in three stages to suit the country’s resource profile:
- In the first stage, heavy water reactors fuelled by natural uranium would produce plutonium
- The second stage would initially be fuelled by a mix of the plutonium from the first stage and natural uranium. This uranium would transmute into more plutonium and once sufficient stocks have been built up, thorium would be introduced into the fuel cycle to convert it into uranium 233.
- In the final stage, a mix of thorium and uranium will fuel the reactors
India’s first thorium reactor is equipped with passive shutdown systems, core heat removal emergency core coolant system and a gravity driven water pool and a borated water on top of the primary containment vessel. This reactor can operate for four months without any sort of control and is built to last about 100 years. An experimental thorium nuclear reactor is set up at the Bhabha Atomic Research Centre in Mumbai (BARC) for observation.
M.R. Srinivasan, former Chairman of the Indian Atomic Energy Commission stated the Advanced Heavy Water Reactor is the latest design for a next-generation nuclear reactor in India. In its final stages of development, the AHWR is being tested at BARC as part of the third stage of India’s nuclear energy program, which envisages the use of thorium fuel cycles for generating commercial power.
After decades of operating pressurized heavy-water reactors, India is finally ready to start the next stage. A 500 MW Prototype Fast Breeder Reactor at Kalpakkam is set to achieve criticality soon and four more fast breeder reactors have been sanctioned. However, experts estimate that it would take India many more FBRs and at least another decade before it can build up a sufficient fissile material inventory to launch the third stage.
Differences between a Uranium Reactor and a Thorium Reactor:
|Regular Uranium Reactor||Thorium Reactor|
|Uses Uranium a radioactive material||Uses Thorium has the chief raw material|
|The nuclear waste disposal of uranium is a major hazard, as the radioactive waste emits radioactive rays for thousands of years||Thorium absorbs the nuclear waste and this waste is much less radioactive and decays sooner. Thorium’s byproducts produce more neutrons than conventional nuclear fuel, and more the neutrons huge amounts of energy is produced, less fuel is consumed and less waste is produced|
|Uranium-235 is purified and enriched and during the reaction, it leaves behind plutonium- 239 which is highly radioactive. These reactors require a lot of engineering and the waste generated by them is radioactive for thousands of years.||Thorium reactor does not emit any radioactivity into the atmosphere|
|The risk of meltdown is high in the present reactors, which has led to disasters like Fukushima and Chernobyl||Thorium reactors have zero risk of reactor meltdown|
|The risk of making nuclear bomb is high as it produces huge amounts of hydrogen.||Thorium cannot be used to manufacture atomic bombs|
Drawbacks of Thorium reactor:
• Thorium is chemically inert making it difficult to chemically process.
• It is not suitable for reactors that require excellent neutron economy.
• Thorium melts at 550 degrees; therefore high temperature is required to produce high quality solid fuel.
• Limited graphite lifetime.
The experimental Indian reactor will demonstrate the use of thorium and low enriched uranium, which is available in the world market. This is an important step to reduce the consumption and import of fossil fuels in India as well as to combat the climate change. However, we have to wait and watch if this powerful energy source will be considered eco-friendly with no harm caused to nature.