Kalpakkam fast breeder reactor attains criticality: why this is a ‘defining step’ in India’s 3-stage n-programme

The core of the 500 MWe FBR, developed by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), has achieved criticality, meaning it has initiated a self-sustaining chain of nuclear fission. Unlike Stage 1 Pressurised Heavy Water Reactors (PHWRs) which use natural uranium, FBRs utilize a Uranium-Plutonium mixed oxide (MOX) fuel. They are called 'breeders' because they transmute a fertile blanket of U-238 into more fissile material than they consume. This unique 'higher breeding' capability is essential to rapidly scale up power capacity and enlarge the inventory of plutonium and Uranium-233 needed for the final stage of the program.

The three-stage program was strategically conceived by Homi Bhabha to bypass India's modest uranium reserves and exploit its massive thorium wealth. Thorium is abundantly found in coastal and inland placer sands, specifically as Monazite deposits in states like Kerala, Tamil Nadu, Andhra Pradesh, and Odisha. However, natural Thorium-232 is a 'fertile' material rather than a 'fissile' one, meaning it cannot initiate a nuclear chain reaction on its own. It must first be irradiated in an FBR to transmute into fissile Uranium-233, making the successful operation of FBRs an unavoidable bridge to the third stage.

Nuclear energy provides clean, reliable baseload power that is crucial for balancing India's economic growth with its net-zero emission targets. The Department of Atomic Energy aims to aggressively expand this sector, targeting an installed nuclear capacity of 22,480 MWe by 2032. While the India-US Civil Nuclear Agreement significantly accelerated Stage 1 by allowing imported uranium for domestic reactors, true long-term energy independence requires closing the nuclear fuel cycle indigenously. The commercial deployment of FBRs and the eventual transition to thorium-based reactors will permanently insulate India from global uranium supply shocks and volatile fossil fuel markets.