Context

Recently, the Kakrapar atomic power plant-3 achieved criticality.

About

• Almost 25 years after the last unit was commissioned at Kakrapar Atomic Power Plant, the Nuclear Power Corporation of India Limited (NPCIL) has achieved criticality of the third unit of 700 MWe at the plant in Tapi district.
• NPCIL has seven more reactors under construction which include the fourth unit of 700 MWe at Kakrapar. These reactors are expected to be completed and achieve criticality next year onwards.
  

  Background

  • The first two units at Kakrapar of 220 MWe (Megawatt electric) each were based on Canadian technology. The third unit is fully indigenous.
  • The first Pressurised Heavy Water Reactor (PHWR) of 220 MWe was commissioned on May 6, 1993, while the second unit of similar capacity was commissioned on September 1, 1995.
  • The third reactor at Kakrapar is the front runner in a series of 16 indigenous 700 MWe PHWRs which are under various stages of development.
  • The work on the third and fourth units of 700 MWe each began in 2011. The fuel loading for the reactor core was completed by mid-March 2020.

  Kakrapar-3 (KAPP-3)

  • KAPP-3 is India’s first 700 MWe unit, and the biggest indigenously developed variant of the Pressurised Heavy Water Reactor.
  • The indigenous 700 MWe PHWRs have advanced safety features like steel-lined inner containment, passive decay heat removal system, containment spray system, hydrogen management system, among others.
  • Until now, the biggest reactor size of the indigenous design was the 540 MWe PHWR, two of which have been deployed in Tarapur, Maharashtra.

  Reactors & Criticality

  • Reactors are the heart of an atomic power plant, where a controlled nuclear fission reaction takes place that produces heat, which is used to generate steam that then spins a turbine to create electricity.
  • Fission is a process in which the nucleus of an atom splits into two or smaller nuclei, and usually some by-product particles.
  • When the nucleus splits, the kinetic energy of the fission fragments is transferred to other atoms in the fuel as heat energy, which is eventually used to produce steam to drive the turbines.
  • For every fission event, if at least one of the emitted neutrons on average causes another fission, a self-sustaining chain reaction will take place.
  • A nuclear reactor achieves criticality when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.
  • Criticality is the first step towards power production.

  Significance

  • The PHWRs, which use natural uranium as fuel and heavy water as moderator, is the mainstay of India’s nuclear reactor fleet.
  • The operationalisation of India’s first 700MWe reactor marks a significant scale-up in technology, both in terms of optimisation of its PHWR design.
  • It addresses the issue of excess thermal margins, and an improvement in the economies of scale, without significant changes to the design of the 540 MWe reactor.
    • ‘Thermal margin’ refers to the extent to which the operating temperature of the reactor is below its maximum operating temperature.
  • The 700MWe reactors will be the backbone of a new fleet of 12 reactors to which the government accorded administrative approval and financial sanction in 2017, and which are to be set up in fleet mode.
  • As India works to ramp up its existing nuclear power capacity of 6,780 MWe to 22,480 MWe by 2031, the 700MWe capacity would constitute the biggest component of the expansion plan.
    • Currently, nuclear power capacity constitutes less than 2% of the total installed capacity of 3,68,690 MW (end-January 2020).
  • As the civilian nuclear sector gears up for the next frontier, building a 900 MWe Pressurised Water Reactor (PWR) of indigenous design, the experience of executing the larger 700MWe reactor design will come in handy, especially about the improved capability of making large pressure vessels.
    • This is alongside isotope enrichment plants being developed to supply part of the required enriched uranium fuel to power these new generation reactors over the next decade or so.