India’s 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu achieved first criticality on April 6, marking an important stage in the country’s nuclear energy programme. Prime Minister Narendra Modi described the development as a “historic milestone”, saying it reflects India’s commitment to clean energy and self-reliance.
The reactor was designed by the Indira Gandhi Centre for Atomic Research (IGCAR) and constructed by Bharatiya Nabhikiya Vidyut Nigam Ltd (BHAVINI), both under the Department of Atomic Energy. The project involved a large number of Indian scientists, engineers and industry partners, with a strong focus on indigenous technology and components.
The PFBR is part of India’s long-term strategy to expand nuclear power capacity and develop advanced fuel technologies.
Here is what the development means and why it matters:
What is first Critically?
First criticality is the stage at which a nuclear reactor achieves a self-sustaining fission chain reaction for the first time.
It does not mean the reactor is fully operational or generating electricity, but it is a crucial step before further testing, power escalation and eventual grid connection.
The PFBR reached this stage after meeting safety requirements set by the Atomic Energy Regulatory Board (AERB), following a detailed review of its systems.
What is Fast Breeder Reactor?
Fast breeder reactors are designed to produce more nuclear fuel than they consume.
Unlike conventional reactors, the PFBR uses uranium-plutonium mixed oxide (MOX) fuel and fast neutrons to convert uranium-238 into plutonium-239, which can be reused as fuel.
This “breeding” process significantly improves fuel efficiency and reduces dependence on fresh uranium supplies.
How does it fit into India’s Nuclear strategy?
India’s nuclear programme is structured in three stages.
The first stage uses pressurised heavy water reactors fuelled by natural uranium.
The second stage, where the PFBR fits in, focuses on fast breeder reactors that generate more fissile material.
The third stage aims to use thorium — a resource India has in abundance — by converting thorium-232 into uranium-233 for advanced reactors.
The PFBR is a critical bridge between the existing uranium-based reactors and future thorium-based systems.
Why does this matter ?
Fast breeder reactors are expected to play an important role in expanding India’s low-carbon energy capacity by providing reliable base-load power.
The technology is pursued by only a few countries, including Russia, China and India, because it is technically complex and expensive. India’s PFBR is among the limited number of such reactors being developed globally as part of a long-term strategy to eventually utilise the country’s vast thorium reserves.
The project also strengthens India’s expertise in areas such as nuclear fuel cycles, advanced materials and reactor design, which are essential for next-generation nuclear systems.
With first criticality achieved, the PFBR has moved a step closer to electricity generation, marking progress in India’s efforts to expand clean energy capacity and advance indigenous nuclear technology.
What technologies does it use?
The PFBR uses liquid sodium as a coolant, allowing operation at high temperatures and improving efficiency.
It also adopts a closed fuel cycle, enabling the recycling of nuclear material, which reduces waste and enhances sustainability.
In the future, the reactor is expected to support thorium utilisation through transmutation processes.
What are the types of nuclear reactors and their operational status in India-
Pressurised Heavy Water Reactors (PHWRs): These reactors use heavy water as a coolant and moderator to slow neutrons and sustain a controlled nuclear chain reaction using natural uranium fuel. They form the backbone of India’s nuclear power programme, with most of the country’s operational reactors based on this design and several new 700 MWe units under construction.
Pressurised Water Reactors (PWRs): These use ordinary water under high pressure as both coolant and moderator, transferring heat from the reactor core to a separate water loop that produces steam to drive turbines. Two Russian-designed VVER reactors are operational at Kudankulam in Tamil Nadu, with four more units under construction.
Boiling Water Reactors (BWRs): In these reactors, water boils directly inside the reactor core to produce steam that drives turbines. India operates two BWR units at the Tarapur Atomic Power Station in Maharashtra, and no new BWRs are planned.
Fast Breeder Reactors (FBRs): These reactors use fast neutrons and liquid sodium coolant and are designed to produce more nuclear fuel than they consume by converting uranium-238 into plutonium-239. The 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam has achieved first criticality and is under commissioning, while the smaller Fast Breeder Test Reactor (FBTR) operates there for research.
Small Modular Reactors (SMRs): These are compact reactors based on nuclear fission but designed in smaller, modular units that can be factory-built and assembled on site. None are operational in India yet, though indigenous designs such as the Bharat Small Modular Reactor (BSMR-200) and SMR-55 are being planned.
Advanced reactors: Designs such as high-temperature gas-cooled reactors and molten salt reactors use alternative coolants like helium or molten salts to achieve higher efficiency and improved safety features, and are currently at the research or conceptual stage in India.
Road Ahead
Following first criticality, the PFBR will undergo phased power ascension, extensive performance testing, and safety validation before being connected to the grid for commercial electricity generation. Successful operation of this prototype will pave the way for constructing larger 600 MWe fast breeder reactors at Kalpakkam and other sites. In the longer term, it strengthens India’s roadmap to unlock its abundant thorium reserves, enabling a self-sustaining and sustainable nuclear power programme for decades to come.
