Kalpakkam’s Milestone: Assessing India’s Nuclear Energy Strategy

India’s Prototype Fast Breeder Reactor has just reached criticality signifying operationality in the second stage of its nuclear program. Once India reaches the third stage, India is slated to be able to sustain its energy needs for centuries. But what does reaching the third stage mean for India and its energy supply? And what role does the country’s thorium reserves play in its nuclear strategy?

What has happened?

India’s Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu was announced to have attained criticality on April 6, 2026. The reactor has a capacity of 500 Megawatts electric which is enough electricity to power roughly four to five lakh average Indian homes simultaneously. Prime Minister Narendra Modi has termed the achievement a “defining step” in India’s journey towards achieving India’s nuclear programme. 

The reactor does not generate electricity yet, however it has attained criticality which refers to the stage where the chain reaction within the nuclear reactor becomes sustainable. A chain reaction happens when each fission event or split in the neutron produces exactly enough neutrons to trigger a subsequent one at sustainable risk. Therefore, criticality essentially indicates constancy in the production of neutrons within the reactor which is a significant condition to be fulfilled for the reactor to sustain itself. 

After attaining criticality, the reactor is now headed to attain operationality, achieving which India will be only the second country in the world to have a commercially operating fast breeder reactor. The only other country being Russia.

How the PFBR works

The PFBR has been designed indigenously by the Indira Gandhi Centre for Atomic Research (IGCAR) at Kalpakkam. It is a breeder reactor which is a powerful type of power reactor that has the ability to produce more fuel than it burns. The breeder reactor is the only reactor that can perform this function on a commercial scale.

The PFBR runs on uranium-plutonium Mixed Oxide (MOX) fuel which comprises ceramic pellets made by blending uranium and plutonium oxides together. The plutonium has been taken from the spent, used-up first stage of India’s nuclear program. This happens when uranium fuel runs in a first-stage reactor and the uranium atoms are bombarded with neutrons which leads to most of the uranium to split (fission) to produce energy. Some uranium atoms, however, end up absorbing a neutron and transform into plutonium through a nuclear reaction. Therefore, the waste from the first stage contains newly created plutonium along with the leftover fission waste and uranium.

During the second stage, where the PFBR currently operates, the waste is then chemically treated to separate and extract this plutonium from the rest of the waste. That extracted plutonium is then blended with uranium oxide to make the MOX ceramic pellets.

The PFBR circulates liquid sodium to act as a coolant instead of water for the intense heat generated inside the reactor. Molten sodium (200 Celsius degrees) is more efficient at transferring heat than water and does not slow the fast-moving neutrons the reactor creates.

India’s Nuclear Programme

Dr. Homi Jehangir Bhabha, known as the Father of Nuclear Program in India, laid down  India’s three-stage nuclear program designed around India’s problem of limited domestic uranium reserves. Although India suffers from such a shortage of uranium, we have a plethora of thorium reserves in the country which is what forms the backbone of the nuclear program envisioned by Dr. Homi. 

India’s nuclear strategy, unlike most countries, revolves around thorium reserves and not uranium. Uranium is a naturally occurring radioactive element which decays over time and releases energy in the process. Uranium occurs in two slightly differing forms called isotopes called the U-238 and the U-235 (the difference exists due to the difference in the number of neutrons in the nucleus of the element).

Natural uranium as found in the Earth's crust is largely a mix of these two wherein U-238 accounts for 99.3% and U-235 accounts for 0.7%. It is the U-235 isotope that can readily be split, yielding a lot of energy and is used for nuclear power generation. Interestingly, a chicken-egg sized amount of uranium fuel can provide as much electricity as 88 tonnes of coal.

On the other hand, thorium is a naturally occurring radioactive metal. Thorium exists in nature in a single isotopic form (Th-232)  which decays very slowly. It is ‘fertile’ rather than fissile, and can only be used as a fuel in nuclear power generation when used with a fissile material. India holds the world’s highest thorium reserves at 846,000 tonnes, followed by Brazil at 632,000 tonnes, followed by Australia and the US both at 595,000 tonnes of reserves.

Unlike uranium which is scarce in India (found in states, including Jharkhand, Rajasthan, Andhra Pradesh, Telangana and Karnataka, as well as regions of the Himalayan belt), thorium is found in abundance in the country and is contained in the mineral monazite occurring in the beach sand placer deposits along the eastern and western coasts of the country as well as the inland places in parts of Kerala, Tamil Nadu, Odisha, Andhra Pradesh, West Bengal, Jharkhand and Chhattisgarh. India accounts for 25% of the world’s thorium reserves which is why the nuclear strategy.

This is essentially why India is banking on thorium, rather than uranium for its nuclear strategy and in the long-run, its energy supply.

FIRST STAGE

The first stage runs on indigenously built Pressurized Heavy Water Reactors (PHWRs) which run on natural uranium which powers the reactors. Some of the uranium, as mentioned before, ends up absorbing neutrons which leads to the genesis of plutonium as a byproduct. This stage uses water as the primary coolant. 

The first PHRW was finalized to be built in 1964 and the first prototype called Rajasthan-1 was built as a collaborative endeavour between Nuclear Power Corporation of India Limited (NPCIL) and Atomic Energy of Canada Ltd (AECL). Rajasthan-1 was modelled on Canada’s Douglas Point reactor and the subsequent PHWRs used the same prototype. 

The first stage has already been achieved by India, which has been working for years to achieve sustainability in the second stage of the program.

SECOND STAGE

The second stage is the one India is currently working on. This stage uses the uranium and plutonium extracted from the waste produced in stage 1 termed as MOX fuel. This fuel is designed in a way that it is enveloped by uranium which becomes plutonium during this stage. This is the reason behind why the stage is called Fast Breeder Reactors because it essentially breeds more plutonium during this stage. Therefore, the reactor does not only consume the plutonium but also produces more of it. 

Here is where the role of thorium comes into play. Thorium is a fertile material which can absorb a neutron to transform into another element. Inherently, thorium cannot be used as nuclear fuel because it cannot sustain a fission chain reaction. However, when thorium is added during the second stage, it absorbs the other neutrons in the reactor which leads to the formation of Uranium-233 which, unlike thorium, is a fissile material. 

THIRD STAGE

Uranium-233 created in stage 2 is then used as fuel for stage 3 in Advanced Heavy Water Reactors (AHWRs). This is where both uranium and thorium will be used. Uranium will produce nuclear energy as it undergoes fission whereas the added thorium will absorb neutrons released by the fission and will, in turn, create more uranium. At this stage, the fuel sustains the cycle itself as thorium creates the new uranium to carry on the process creating a self-feeding cycle. This utilizes India’s thorium reserves to their full extent and once achieved, will be a gamechanger for India’s energy needs.

Why is nuclear energy important for India?

India hosts a population of 1.4 billion people and has one of the fastest growing economies in the world. At the same time, the country has pledged to cut down its emissions to net zero by 2070. Therefore, it requires a robust plan to support its energy needs that are, as of now,  heavily coal-dependent which remains the largest source of India’s energy supply. This makes nuclear energy an important part of the country’s long term energy strategy. 

In its Nuclear Energy Mission, outlined during Budget Session 2025-26, the Indian government announced that the country aims to achieve 100 GW nuclear power generation capacity by 2047. Additionally, at the 26th session of the Conference of the Parties (COP26) to the United Nations Framework Convention on Climate Change (UNFCCC), India put forth the five critical elements of its climate action strategy called Panchamrit:

a) Reach 500GWNon-fossil energy capacity by 2030

b) 50 per cent of its energy requirements from renewable energy by 2030

c) Reduction of total projected carbon emissions by one billion tonnes from now to 2030

d) Reduction of the carbon intensity of the economy by 45 per cent by 2030, over 2005 levels

e) Achieving the target of net zero emissions by 2070.

These highlight India's attempt to shift away from non-renewable sources of energy towards a more sustainable energy strategy, making the news of reaching criticality come at an important juncture for the goal since nuclear power can play a major role in helping India achieve the Panchamrit. 

What happens if India reaches the third stage?

As of now, no country in the world has yet reached stage 3 in this process. Countries such as Japan have tried and reached stage 2 before, however, being unable to sustain it, the reactor was later decommissioned in 2016.

Once India achieves this feat, the country, which is currently one of the world’s largest importers of fossil fuels, will be able to drastically reduce its dependence on foreign energy sources.

There would be abundance in electricity generation which could lower the electricity rates in the country. The reduced dependence on coal would also lead to lesser emissions which would positively impact the country’s air quality. Most significantly, India would become less vulnerable to global energy disruptions as recently witnessed in the 2026 West Asia conflict.

With regards to uranium imports that India imports currently gets from countries such Kazakhstan, achieving stage 3 would practically eliminate this need, further reducing India’s dependency on foreign energy reserves.

Completing stage 3 will make India’s nuclear strategy inherently self-reliant and would empower India to further bolster its presence on the global stage, which factoring in the increasing turbulent geopolitical landscape, is definitely the need of the hour.