India's first indigenous Fast Breeder Reactor (FBR) at Kalpakkam in Tamil Nadu has successfully attained criticality, marking a pivotal achievement in the country's three-stage nuclear program. Prime Minister Narendra Modi described this event as a 'defining step' in advancing India's civil nuclear capabilities, highlighting the reactor's role in harnessing the nation's thorium reserves. The FBR is designed to initiate a self-sustaining nuclear fission reaction, which will ultimately lead to the generation of power from the 500-megawatt electric reactor. The completion of core loading, which involved placing nuclear fuel assemblies inside the reactor, was finalized in March 2024. Initially, the reactor will utilize uranium-plutonium mixed oxide (MOX) fuel, with a Uranium 238 blanket to produce additional fuel through nuclear transmutation. The project, initiated two decades ago, has seen various delays but is now positioned to enhance India's nuclear energy capabilities, making it the second country after Russia to operate a commercial FBR.