India's nuclear energy programme saw the 500 MWe Prototype Fast Breeder Reactor successfully attain first criticality in April 2026. What does 'first criticality' signify?

When a nuclear reactor achieves 'first criticality,' it marks the moment a self-sustaining nuclear chain reaction begins. This means that for every atomic nucleus that splits, releasing energy and neutrons, at least one of those neutrons goes on to cause another nucleus to split, continuing the process. This state is often referred to as 'controlled fission' because the reaction is carefully managed to maintain a stable rate, preventing it from escalating uncontrollably or dying out.

In essence, controlled fission is the cornerstone of nuclear power generation. Reactors are equipped with control rods, typically made of materials like boron or cadmium, which absorb excess neutrons. By carefully adjusting the position of these rods, operators can precisely regulate the number of neutrons available to cause further fissions, ensuring a steady and safe energy output. The first successful demonstration of a controlled, self-sustaining nuclear chain reaction occurred in December 1942 with the Chicago Pile-1, a pivotal moment in scientific history.

India's 500 MWe Prototype Fast Breeder Reactor (PFBR) reaching first criticality in April 2026 is a significant milestone for the nation's ambitious nuclear energy program. Unlike conventional reactors, fast breeder reactors are designed to produce more fissile fuel than they consume. The PFBR, a sodium-cooled reactor, will utilize uranium-plutonium mixed oxide fuel and is crucial to India's three-stage nuclear strategy, which aims to leverage its abundant thorium reserves for long-term energy security. This achievement underscores India's commitment to indigenous nuclear technology and a sustainable energy future.