Largest indigenously developed N-plant unit in Gujarat starts ops at full capacity

Largest indigenously developed N-plant unit in Gujarat starts ops at full capacity

Subject: Science and technology

Section: Nuclear Technology

Context:

The third unit of the indigenously developed 700-megawatt electric (MWe) nuclear power reactor at the Kakrapar Atomic Power Project (KAPP3) in Gujarat has commenced operations at full capacity.

Details:

• This comes a little over three years since the unit achieved its ‘first criticality’ – a technical term that signifies the initiation of a controlled, but sustained nuclear fission reaction – in July 2020.
• On June 30 this year, the unit had started commercial operations.
• India is further planning to build a 900 MWe Pressurised Water Reactors (PWRs) of indigenous design.

About kakrapar nuclear power plant:

• Kakrapar Atomic Power Station is a nuclear power station in India, which lies in the proximity of Mandvi, Surat and Tapi river in the state of Gujarat.
• Four units of the 700MWe reactor are being constructed at Kakrapar (KAPP-3 and 4) and Rawatbhata (RAPS-7 and 8) site in Rajasthan currently.
• Originally expected to be commissioned in 2015.
• Built by: Larsen & Tubro (L&T).
• operated by: State-owned Nuclear Power Corporation of India (NPCIL).
• It will help in India’s expansion plan of Nuclear Power Plant capacity from 7480 MWe to 22480 MWe by 2031.
• Currently, nuclear power capacity constitutes around 2 percent of the total installed capacity of 4,17,668 MW.

Significance of KAPP-3:

• KAPP-3 is the country’s first 700 MWe unit and the biggest indigenously developed variant of the Pressurised Heavy Water Reactor (PHWR).
• For India, the operationalisation of its first 700MWe reactor is a significant scale up in technology, both in terms of:
  • the optimisation of its PHWR design as the new 700MWe unit addresses the excess thermal margins (thermal margin refers to the extent to which the operating temperature of the reactor is below its maximum operating temperature) — and
  • marks an improvement in the economies-of-scale, without significant design changes to the 540 MWe reactor.

• Now India has experience in:
  • Making large size pressure vessels
  • Own isotope enrichment plants

Pressurised Heavy Water Reactor (PHWR):

• A PHWR is a nuclear reactor that uses heavy water (deuterium oxide D2O) as its coolant and neutron moderator.
• PHWRs frequently use natural uranium as fuel, but sometimes also use very low enriched uranium.
• The heavy water coolant is kept under pressure to avoid boiling, allowing it to reach higher temperature (mostly) without forming steam bubbles, exactly as for a pressurized water reactor.
• While heavy water is very expensive to isolate from ordinary water (often referred to as light water in contrast to heavy water), its low absorption of neutrons greatly increases the neutron economy of the reactor, avoiding the need for enriched fuel.
• The high cost of the heavy water is offset by the lowered cost of using natural uranium and/or alternative fuel cycles.
• As of the beginning of 2001, 31 PHWRs were in operation, having a total capacity of 16.5 GW(e), representing roughly 7.76% by number and 4.7% by generating capacity of all current operating reactors.
• Till now, the biggest reactor of indigenous design was the 540 MWe PHWR, two of which have been deployed in Tarapur, Maharashtra.

Safety features of PHWR:

• In terms of safety features, the PHWR technology scores high
• The biggest advantage of the PHWR design is the use of thin walled pressure tubes instead of large pressure vessels used in pressure vessel type reactors.
• This results in a distribution of pressure boundaries to a large number of small diameter pressure tubes and thereby lowers the severity of the consequence of an accidental rupture of the pressure boundary than in a pressure vessel type reactor.
• Additionally, the 700 MWe PHWR design has enhanced safety through dedicated ‘Passive Decay Heat Removal System’, which has the capability of removing decay heat (the heat released as a result of radioactive decay) from the reactor core without requiring any operator actions, on the lines of similar technology adopted for Generation III+ plants to negate the possibility of a Fukushima type accident that happened in Japan in 2011.
• The 700 MWe PHWR unit, like the one deployed in KAPP, is 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.