This week, India’s three-stage nuclear power programme crossed a milestone. The indigenously designed-and-built 500-megawatt-electrical (MWe) fast breeder reactor at Kalpakkam in Tamil Nadu attained criticality—the point at which sustained and controlled nuclear fission chain reaction begins with stable power output, marking the transition to the operational phase that would generate electricity. This marks India’s entry into the second of its nuclear programme’s three stages.
The Department of Atomic Energy designed a three-stage programme because though India has limited uranium reserves, it holds a quarter of the global thorium deposits that can be extracted from monazite sand on the beaches of Kerala, Odisha and Tamil Nadu. In the first stage, natural uranium is used as fuel in pressurised heavy water reactors to generate power. The spent fuel from these reactors produces plutonium, the primary fuel for the second stage, in which fast-breeder reactors generate more fuel than they consume. The prototype fast-breeder reactor at Kalpakkam will breed Uranium-233 from thorium, laying the groundwork for stage three, which will use the Uranium-233 bred in the second stage as fuel.
Today, nuclear power accounts for just 8.78 gigawatt of India’s total installed capacity of more than 520 GW. But experts project a three-fold growth in the nuclear capacity to reach 22.38 GW by 2031-32. And thorium holds the key for that leap.
A broader view of the sector makes India’s clean and reliable energy roadmap clearer. The country today has 25 nuclear reactors that have achieved first-stage criticality and are generating power; 11 more are under construction. The Nuclear Energy Mission has also allocated ₹20,000 crore for indigenously-designed small modular reactors, at least five of which are expected to be operational by 2033. The Bhabha Atomic Research Centre is developing the next-generation plants—200-MWe and 55-MWe small modular reactors and a 5-MW-thermal high-temperature gas-cooled reactor for producing hydrogen. The Sustainable Harnessing and Advancement of Nuclear energy for Transforming India Act, 2025 streamlines the legal framework to enable private participation in nuclear power generation under strict regulations to encourage collaboration and investment.
The roadmap looks encouraging. Kalpakkam gaining criticality is a turning point for the way ahead—one of technological self-reliance leading to energy security and India’s net-zero commitments for 2070.