Three-Stage Nuclear Power:- India’s three-stage nuclear power program 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 program is on enabling the thorium reserves of India to be utilized 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.
• However, at present thorium is not economically viable because global uranium prices are much lower.
• The recent Indo-US Nuclear Deal and the NSG waiver, which ended more than three decades of international isolation of the Indian civil nuclear program, have created many hitherto unexplored alternatives for the success of the three-stage nuclear power program.
• Thorium itself is not a fissile material and thus cannot undergo fission to produce energy.
• Instead, it must be transmuted to uranium-233 in a reactor fueled by other fissile materials [plutonium-239 or uranium-235].
• The first two stages, natural uranium-fueled heavy water reactors, and plutonium-fueled fast breeder reactors, are intended to generate sufficient fissile material from India’s limited uranium resources so that all its vast thorium reserves can be fully utilized in the third stage of thermal breeder reactors.

Stage I – Pressurized Heavy Water Reactor [PHWR]

• In the first stage of the program, natural uranium-fueled pressurized heavy water reactors (PHWR) produce electricity while generating plutonium-239 as a by-product.

[U-238 → Plutonium-239 + Heat]                                                                 

[In PWHR, enrichment of Uranium to improve the concentration of U-235 is not required. U-238 can be directly fed into the reactor core]

[Natural uranium contains only 0.7% of the fissile isotope uranium-235. Most of the remaining 99.3% is uranium-238 which is not fissile but can be converted in a reactor to the fissile isotope plutonium-239].

[Heavy water (deuterium oxide, D 2O) is used as a moderator and coolant in PHWR].

• PHWRs was a natural choice for implementing the first stage because they had the most efficient reactor design [uranium enrichment not required] in terms of uranium utilization.
• India correctly calculated that it would be easier to create heavy water production facilities (required for PHWRs) than uranium enrichment facilities (required for LWRs).
• Almost the entire existing base of Indian nuclear power (4780 MW) is composed of first-stage PHWRs, with the exception of the two Boiling Water Reactor (BWR) units at Tarapur.

Stage II – Fast Breeder Reactor

• In the second stage, fast breeder reactors (FBRs) [moderators not required] would use 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 fuel transmutes to additional plutonium-239.

Why should Uranium-238 be transmuted to Plutonium-239?                             

Uranium-235 and Plutonium-239 can sustain a chain reaction. But Uranium-238 cannot sustain a chain reaction. So it is transmuted to Plutonium-239.

But Why U-238 and not U-235?

Natural uranium contains only 0.7% of the fissile isotope uranium-235. Most of the remaining 99.3% is uranium-238.

• Thus, the Stage II FBRs are designed to “breed” more fuel than they consume.
• Once the inventory of plutonium-239 is built up thorium can be introduced as a blanket material in the reactor and transmuted to uranium-233 for use in the third stage.
• The surplus plutonium bred in each fast reactor can be used to set up more such reactors, and might thus grow the Indian civil nuclear power capacity to the point where the third-stage reactors using thorium as fuel can be brought online
• As of August 2014, India’s first Prototype Fast Breeder Reactor at Kalpakkam had been delayed – with the first criticality expected in 2015, 2016 and it drags on.

Stage III – Thorium Breeder Reactor

• 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 replies given in Q&A in the Indian Parliament on two separate occasions, 19 August 2010 and 21 March 2012, large-scale thorium deployment is only to be expected 3–4 decades after the commercial operation of fast breeder reactors. [2040-2070]
• As there is a long delay before direct thorium utilization in the three-stage program, the country is now looking at reactor designs that allow more direct use of thorium in parallel with the sequential three-stage program
• Three options under consideration are the Accelerator Driven Systems (ADS), Advanced Heavy Water Reactor (AHWR), and Compact High-Temperature Reactor

Prototype Fast Breeder Reactor at Kalpakkam                                                   

• The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe Fast Breeder Nuclear Reactor presently being constructed at the Madras Atomic Power Station in Kalpakkam, India.
• The Indira Gandhi Centre for Atomic Research (IGCAR) is responsible for the design of this reactor.
• As of 2007, the reactor was expected to begin functioning in 2010 but now it is expected to achieve its first criticality in March-April 2016.
• Construction is over and the owner/operator, Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), is awaiting clearance from the Atomic Energy Regulatory Board (AERB).
• Total costs, originally estimated at 3,500 crores are now estimated at 5,677 crores.
• The Kalpakkam PFBR is using uranium-238, not thorium, to breed new fissile material, in a sodium-cooled fast reactor design.
• The surplus plutonium or uranium-233 for thorium reactors [U-238 transmutes into plutonium] from each fast reactor can be used to set up more such reactors and grow the nuclear capacity in tune with India’s needs for power.
• The fact that PFBR will be cooled by liquid sodium creates additional safety requirements to isolate the coolant from the environment since sodium explodes if it comes into contact with water and burns when in contact with air.             
• Name the research reactors set up by the Department of Atomic Energy.

Apsara is the oldest of India’s research reactors. The reactor was designed by the Bhabha Atomic Research Center (BARC) and built with assistance from the United Kingdom (which also provided the initial fuel supply consisting of 80 percent enriched uranium). Apsara first went critical on 4 August 1956.

The researcher reactors set up by DAE so far, have been Apsara (1mW, Fuel: Enriched Uranium-Aluminium alloy), CIRUS (40MW, Fuel: Natural Uranium), Zerlina (Zero Energy, Natural Uranium), Purnima I-III (Fuel: Plutonium/ Uranium-233), Dhruva (100MW, Fuel: Natural Uranium) at Trombay (Maharashtra), and Kamini (30KW, Fuel: Uranium-233-Aluminium alloy) and Fast Breeder Test Reactor (40MW, Fuel: Uranium- Plutonium carbide) at Kalpakkam (Tamil Nadu). Of the research reactors, Zerlina was decommissioned in 1984, and the Purnima series made way for Kamini.

Dhruva, CIRUS, and Apsara are used for producing radioisotope bodies they’re used in research and development relating to nuclear technologies and materials, applied and basic research, and training. KAMINI is used mainly for the radiography of various materials, and the Fast Breeder Test Reactor (FBTR) at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam is a sodium-cooled, loop-type fast reactor that serves as a valuable test bed for the development of fuel and structural material for future fast reactors in India.

According to the Department of Atomic Energy (DAE), 21 new nuclear power reactors with a total installed capacity of 15,700 MW are expected to be set up in the country by 2031.

The Department of Atomic Energy has taken up the development of fast breeder reactors which enable utilizing Thorium as fuel for power reactors. Simultaneously, it is proposed to set up high-flux research reactors to develop new fuel designs in order to economize on the use of nuclear fuels.

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