NEW DELHI: In a big boost for India’s civil nuclear energy production, the indigenously designed and built Prototype Fast Breeder Reactor (PFBR) at Kalpakkam in Tamil Nadu has attained criticality.Congratulating Indian scientists and engineers on the reactor attaining criticality, PM Narendra Modi posted on X, “Today, India takes a defining step in its civil nuclear journey, advancing the second stage of its nuclear programme. “This advanced reactor, capable of producing more fuel than it consumes, reflects the depth of our scientific capability and the strength of our engineering enterprise. It is a decisive step towards harnessing our vast thorium reserves in the third stage of the programme. A proud moment for India,’ the PM further said.Criticality marks the point at which a nuclear reactor achieves a self-sustaining chain reaction. This is a key milestone before full power generation and indicates that the reactor core is functioning as designed.PFBR is a pool-type, sodium-cooled fast breeder reactor with a capacity of 500 MWe (1,253 MW thermal). It uses mixed oxide (MOX) fuel comprising uranium-238 and plutonium-239. The reactor is a key step for India to reduce its dependence on imported uranium and establish a closed nuclear fuel cycle.The PFBR differs from other nuclear reactors in India by using fast neutrons and liquid sodium coolant to produce more plutonium than it consumes, directly enabling the second stage of India’s three-stage nuclear power programme. Unlike the existing Pressurized Heavy Water Reactors (PHWRs) that use uranium, PFBR burns Uranium-Plutonium mixed oxide (MOX) fuel and serves as a vital step towards using India's vast thorium reserves.PFBR has been fully designed and built by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), a public sector enterprise, with significant contribution from more than 200 Indian industries, including MSMEs. Once it is commissioned, India will only be the second country after Russia to have a commercial operating Fast Breeder Reactor.