India’s third home-built 700 MWe nuclear power reactor has achieved criticality and is expected to start commercial electricity generation soon.

• Pressurised Heavy Water Reactor (PHWR):A pressurised heavy water reactor (PHWR) is a nuclear power reactor, commonly using unenriched natural uranium as its fuel, that uses heavy water (deuterium oxide D2O) as its coolant and moderator
• PHWR Development in India: India’s first PHWR was constructed in the late 1960s at the Rajasthan Atomic Power Station (RAPS-1), built through Indo-Canadian collaboration.

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Criticality of a Nuclear Reactor

• Criticality is the point where a nuclear reactor achieves a self-sustaining chain reaction, with nuclear fission occurring at a steady rate.

• Significance: Achieving criticality marks the reactor’s readiness to generate power, as it indicates stable, controlled nuclear reactions. For India, this represents the progression of its nuclear energy capacity.
• The successful achievement of criticality of RAPP-7 is third after the smooth operation of Kakrapar Atomic Power Station(KAPS) Reactor 3 and 4, the first two 700 MWe PHWRs.

Significance of PHWR in India’s Energy Sector

• Energy Independence: PHWRs can use natural uranium, avoiding reliance on enriched uranium imports.
• Alternate Fuel Cycles: The technology allows the efficient use of alternate fuel cycles, making it versatile and sustainable for long-term energy generation.
• India’s first PHWR, RAPS-1, began the nation’s journey in nuclear power, which continues with advancements like the recent 700 MWe reactor.

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Other Types of Nuclear Reactors

• Light Water Reactors (LWR): Use ordinary water as both coolant and moderator, typically fueled by low-enriched uranium. LWRs come in two types:
  • Pressurised Water Reactor (PWR): Water circulates in a closed loop and transfers heat to a steam generator.
  • Boiling Water Reactor (BWR): Water boils in the reactor core, and the resulting steam directly drives turbines.
• Fast Breeder Reactor (FBR):
  • Fuel: Mixed Oxide (MOX) fuel, made from plutonium and depleted uranium.
  • Coolant: Liquid sodium, with no moderator.
  • Example: The Prototype Fast Breeder Reactor (PFBR) at Kalpakkam is part of India’s second stage in its three-stage nuclear program.

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