Nuclear Energy

[pib] Thorium-Based Nuclear Reactors

Note4Students

From UPSC perspective, the following things are important :

Prelims level : Thorium based reacter

Mains level : India’s Three Stage Nuclear Programme

  • Department of Atomic Energy (DAE) has planned the use of large deposits of Thorium available in the country as a long-term option.

Thorium-Based Nuclear Reactors

  • A three-stage nuclear power programme has been chalked out to use Thorium as a viable and sustainable option, right at the inception of India’s nuclear power programme.
  • The three stage nuclear power programme aims to multiply the domestically available fissile resource through the use of natural Uranium in Pressurized Heavy Water Reactors.
  • It is followed by the use of Plutonium obtained from the spent fuel of Pressurized Heavy Water Reactors in Fast Breeder Reactors.

Why Thorium?

  • The utilization of Thorium, as a practically inexhaustible energy source, has been contemplated during the third stage of the Indian Nuclear Programme.
  • As is the case with generation of electricity from Uranium, there will be no emission of green house gases from Thorium also and therefore, it will be a clean source of energy.
  • It is not possible to build a nuclear reactor using Thorium (Thorium-232) alone due to its physics characteristics.
  • Thorium has to be converted to Uranium-233 in a reactor before it can be used as fuel.

Back2Basics

India’s Three Stage Nuclear Programme

  • 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.
  • Thorium is particularly attractive for India, as it has only around 1–2% of the global uranium reserves, but one of the largest shares of global thorium reserves at about 25% of the world’s known thorium reserves.
  • However, thorium is more difficult to use than uranium as a fuel because it requires breeding, and global uranium prices remain low enough that breeding is unnecessary.

Stage I – Pressurized Heavy Water Reactor

  • In the first stage of the programme, natural uranium fueled pressurised heavy water reactors (PHWR) produce electricity while generating plutonium-239 as by-product.
  • PHWRs was a natural choice for implementing the first stage because it had the most efficient reactor design in terms of uranium utilisation, and the existing Indian infrastructure in the 1960s allowed for quick adoption of the PHWR technology.

Stage II – Fast Breeder Reactor

  • In the second stage, fast breeder reactors (FBRs) would use a mixed oxide (MOX) fuel made from plutonium-239, recovered by reprocessing spent fuel from the first stage, and natural uranium.
  • In FBRs, plutonium-239 undergoes fission to produce energy, while the uranium-238 present in the mixed oxide fuel transmutes to additional plutonium-239.
  • Thus, the Stage II FBRs are designed to “breed” more fuel than they consume.

Stage III – Thorium Based Reactors

  • A Stage III reactor or an advanced nuclear power system involves a self-sustaining series of thorium-232–uranium-233 fuelled reactors.
  • This would be a thermal breeder reactor, which in principle can be refueled after its initial fuel charge – using only naturally occurring thorium.
  • According to the three-stage programme, Indian nuclear energy could grow to about 10 GW through PHWRs fueled by domestic uranium, and the growth above that would have to come from FBRs till about 50GW.
  • The third stage is to be deployed only after this capacity has been achieved. Full exploitation of India’s domestic thorium reserves will likely not occur until after the year 2050.
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