Context: The third unit of the Kakrapar Atomic Power Project (KAPP-3) in Gujarat recently achieved its ‘first criticality’.

  • About KAPP-3
    • State-owned Nuclear Power Corporation of India Ltd (NPCIL) had awarded the reactor-building contract for both KAPP-3 and 4 to Larsen & Toubro.
    • The tariff per unit related to the project was originally calculated to be Rs 2.80 per unit (kWh) at 2010 prices. However, this costing is expected to have seen some escalation.
    • The capital investment for these projects is being funded with a debt-to-equity ratio of 70:30


  • Currently, four units of the 700MWe reactor are being built at Kakrapar (KAPP-3 and 4) and Rawatbhata (RAPS-7 and 8). 
  • 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.

Source: IE

A significant achievement

  • This is considered as a landmark event in India’s domestic civilian nuclear program given that KAPP-3 is the country’s first 700 MWe (megawatt electric) unit.
    • Until now, the biggest reactor size of indigenous design in India was the 540 MWe PHWR, two of which have been deployed in Tarapur, Maharashtra.
  • It is also the biggest indigenously developed variant of the Pressurised Heavy Water Reactor (PHWR).
  • The operationalization of India’s first 700MWe reactor marks a significant scale-up in technology, in terms of 
    • Optimization of its PHWR design — the new 700MWe unit addresses the issue of excess thermal margins.
      • ‘Thermal margin’ refers to the extent to which the operating temperature of the reactor is below its maximum operating temperature.
    • An improvement in the economies of scale, without significant changes to the design of the 540 MWe reactor.
  • Added safety features:
    • There is a use of thin-walled pressure tubes instead of the large pressure vessels that are used in pressure vessel type reactors.
      • This results in lowering the severity of the consequence of an accidental rupture of the pressure boundary.
    •  A dedicated ‘Passive Decay Heat Removal System’
      • It can remove decay heat (released as a result of radioactive decay) from the reactor core without requiring any operator actions.
    • It is also equipped with a steel-lined containment to reduce any leakages, and a containment spray system to reduce the containment pressure in case of a loss of coolant accident.

Achieving criticality

  • Reactors are the heart of any atomic power plant, where a controlled nuclear fission reaction takes place which produces heat, that is used to generate steam that then spins a turbine to create electricity. 
    • Nuclear Fission is a process in which the nucleus of an atom splits into two or more smaller nuclei, and usually some by-product particles. 
  • When the nucleus splits after the Nuclear Fission reaction, 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 nuclear 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 is said to have achieved criticality when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.

India’s targets in nuclear energy

  • 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. 
  • India’s nuclear power capacity currently constitutes less than 2% of the total installed capacity of 3,68,690 MW (end-January 2020).

Evolution of India’s PHWR technology

  • This technology started in India in the late 1960s with the construction of the first reactor, Rajasthan Atomic Power Station, RAPS-1 with a design similar to that of the Douglas Point reactor in Canada, under the joint Indo-Canadian nuclear cooperation.
  • For the second unit (RAPS-2), import content was reduced considerably, and indigenization was undertaken for major equipment.
    • Following the withdrawal of Canadian support in 1974 after Pokhran-1, Indian nuclear engineers themselves completed the construction.
  • From the third PHWR unit (Madras Atomic Power Station, MAPS-1) onward, the evolution and indigenization of the design began
    • The first two units of PHWR using indigenously developed standardized 220 MWe designs were set up at the Narora Atomic Power Station.
  • To realize economies of scale, the design of 540 MWe PHWR was subsequently developed, and two such units were built at Tarapur.


A pressurized heavy-water reactor (PHWR)

  • It is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator. 
  • PHWRs frequently use natural uranium as fuel, sometimes very low enriched uranium.


Image Source: Financial Express