Thorium is Future

The biggest challenge today we all are facing is to provide energy for humanity to sustain and flourish. Developing counties like ours (India) are particularly demanding more energy to tread path of progress and development. Energy is one of the most important component to meet the highest potential of an individual, however we should not keep burning fossils for the same. We need more cleaner, greener ways of power production - Nuclear Energy. In this post, we will particularly focus on Thorium.

This shows the energy inequality

There has been a lot of talk and debate, and of course enthusiasm, about the future of Nuclear Power.  Thorium will play important role in Nuclear Power’s future, particularly for our country (India). So why not know about this extra-ordinary element and its significance?

In this post, we will cover following things:

1. India’s Nuclear Power program
2. Thorium physics
3. How Thorium based Nuclear Power plant works?
4. Why there is still not Thorium based Nuclear Power plant?
5. India and Thorium - Future of Nuclear Power

India’s Nuclear Power Program

Three stages of India’s Nuclear Program for peaceful use of nuclear reaction was formulated by one of the greatest physicist our land - Dr Homi Bhabha, just after independence. He, with the help of benevolent capitalist Tata, started Tata Institute of Fundamental Research. This was later remained as Bhabha Atomic Research Centre (BARC).

Three stages, as envisioned, are as follow

1. Stage I  - Uranium Based Nuclear Power Plant
2. Stage II - Plutonium Based Nuclear Power Plant
3. Stage III - Thorium Based Nuclear Power Plant

India’s nuclear developers have designed an Advanced Heavy Water Reactor (AHWR) specifically as a means for ‘burning’ thorium – this will be the final phase of their three-phase nuclear energy infrastructure plan (see below). The reactor will operate with a power of 300 MWe using thorium-plutonium or thorium-U-233 seed fuel in mixed oxide form.

Most interesting thing about our program is that each stage provides fuels for next. And last stage, Thorium produces least and limited living waste. 

Thorium Physics

Thorium exists in nature in a single isotopic form – Th-232 – which decays very slowly (its half-life is about three times the age of the Earth). Strangely, the lesser popular cousin of Uranium, Thorium was discovered before Uranium. Thorium was discovered in 1829 whereas Uranium was discovered in 1841. Also, Thorium is four times naturally abundant element than Uranium.

Thorium is fertile rather than fissile, and can only be used as a fuel in conjunction with a fissile material such as recycled plutonium. Thorium fuels can breed fissile uranium-233 to be used in various kinds of nuclear reactors.

When pure, thorium is a silvery white metal that retains its lustre for several months.

The most common source of thorium is the rare earth phosphate mineral, monazite, which contains up to about 12% thorium phosphate, but 6-7% on average. Monazite is found in igneous and other rocks but the richest concentrations are in placer deposits, concentrated by wave and current action with other heavy minerals.

Monazite is extracted in India, Brazil, Vietnam and Malaysia, probably less than 10,000 t/yr, but without commercial rare earth recovery, thorium production is not economic at present. Chinese production is unknown. Extraction of thorium as a by-product of rare earth elements (REE) recovery from monazite seems to be the most feasible source of thorium production at this time.

How Thorium based Nuclear Power plant works?

Apart from exiting Nuclear Reactors designs in which Thorium can be used as solid fuel, there are tip more conceptualised reactors which will use Thorium as fuel. They are briefly explained below.

1. Molten Salt Reactors (MSRs): These reactors are still at the design stage but are likely to be very well suited for using thorium as a fuel. The unique fluid fuel can incorporate thorium and uranium (U-233 and/or U-235) fluorides as part of a salt mixture that melts in the range 400-700ºC, and this liquid serves as both heat transfer fluid and the matrix for the fissioning fuel. The fluid circulates through a core region and then through a chemical processing circuit that removes various fission products (poisons) and/or the valuable U-233. The level of moderation is given by the amount of graphite built into the core.

Versus

1. Accelerator Driven Reactors (ADS): The sub-critical ADS system is an unconventional nuclear fission energy concept that is potentially ‘thorium capable’. Spallation neutrons are produced when high-energy protons from an accelerator strike a heavy target like lead. These neutrons are directed at a region containing a thorium fuel, eg, Th-plutonium which reacts to produce heat as in a conventional reactor.

Significance of Thorium

Why there is still not Thorium based Nuclear Power plant?

When development in nuclear fission reaction was taking place, it was time of World War - II. So the researchers and particularly their financial supporters wanted Plutonium as by product, which is used in weaponry.

Uranium got first movers’ advantage and then entire supply chain of fuel fabrication and equipments manufacturing started revolving around Uranium. 

Most of the Thorium deposits are available in developing countries, which is not much appealing to researchers and manufacturers in developed countries.

However, this picture is changing. Biggest impetus in Thorium’s direction is from India. 

India and Thorium - Future of Nuclear Power

Research reactor ‘Kamini’: India has been operating a low-power U-233 fuelled reactor at Kalpakkam since 1996 – this is a 30 kWth experimental facility using U-233 in aluminium plates (a typical fuel-form for research reactors). Kamini is water cooled with a beryllia neutron reflector. The total mass of U-233 in the core is around 600 grams. It is noteworthy for being the only U-233 fuelled reactor in the world, though it does not in itself directly support thorium fuel R&D. The reactor is adjacent to the 40 MWt Fast Breeder Test Reactor in which ThO2 is irradiated, producing the U-233 for Kamini.

In 2009, despite the relaxation of trade restrictions on uranium, India reaffirmed its intention to proceed with developing the thorium cycle. With huge resources of easily-accessible thorium and relatively little uranium, India has made utilisation of thorium for large-scale energy production a major goal in our nuclear power programme:

1. Pressurised heavy water reactors (PHWRs) and light water reactors fuelled by natural uranium producing plutonium that is separated for use in fuels in its fast reactors and indigenous advanced heavy water reactors
2. Fast breeder reactors (FBRs) will use plutonium-based fuel to extend their plutonium inventory. The blanket around the core will have uranium as well as thorium, so that further plutonium (particularly Pu-239) is produced as well as U-233.
3. Advanced heavy water reactors (AHWRs) will burn thorium-plutonium fuels in such a manner that breeds U-233 which can eventually be used as a self-sustaining fissile driver for a fleet of breeding AHWRs.

In all of these stages, used fuel needs to be reprocessed to recover fissile materials for recycling.

India is focusing and prioritising the construction and commissioning of its fleet of 500 MWe sodium-cooled fast reactors in which it will breed the required plutonium which is the key to unlocking the energy potential of thorium in its advanced heavy water reactors. This will take another 15-20 years, and so it will still be some time before India is using thorium energy to any extent. The 500 MWe prototype FBR (fabricated by L&T) under construction in Kalpakkam.

For the world, Fusion is the Future and for India, it’s Thorium!