Context: 

The Prime Minister dedicated to the nation two new Pressurized Heavy Water Reactors (PHWRs) at Kakrapar Atomic Power Station (KAPS).

Kakrapar Atomic Power Project (KAPP): Key Highlights

• The new Unit 3 and Unit 4 at KAPS, each having the capacity to produce 700 MW of electricity are the largest indigenous PHWRs built in the country.
• These two reactors will produce about 10.4 billion units of clean electricity per year and supply energy to states like Gujarat, Maharashtra, MP, Chhattisgarh, Goa and Union Territory of Dadra and Nagar Haveli and Daman and Diu.

About Kakrapar Atomic Power Project (KAPP)

• Kakrapar Atomic Power Project is built by the Nuclear Power Corporation of India Limited (NPCIL), a public sector undertaking of the Department of Atomic Energy.
• Reactor: These reactors are Pressurized Heavy Water Reactors (PHWRs), which use natural uranium as fuel and heavy water as coolant and moderator.
• Coolant: A substance circulated through a nuclear reactor to remove or transfer heat. The most commonly used coolant is water. 
• Moderator: A material, such as ordinary water, heavy water, or graphite, that is used in a reactor to slow down high-velocity neutrons, thus increasing the likelihood of fission.
• Safety Features: The KAPP has advanced safety features like steel lined inner containment, passive decay heat removal system, containment spray system, and hydrogen management system, among others.
  • Passive Decay Heat Removal System  can remove decay heat (released as a result of radioactive decay) from the reactor core without requiring any operator actions.
• India is in the second phase of its three-stage nuclear program, requiring U-235 isotope enrichment of 3 to 5% for power generation.

About Criticality and Nuclear Fission

• A reactor achieves criticality, when each fission event releases a sufficient number of neutrons to sustain an ongoing series of reactions.
  • The first criticality is the start of a controlled fission chain reaction. After the fission, the heat is used to make steam that turns a turbine and produces electricity.
• Process: When a neutron (a particle with no electric charge) hits an atom like Uranium-235, and splits it into smaller atoms. This process is called nuclear fission, and it releases a lot of heat that can be converted into energy. 
• Fissile Material: Uranium-235 is chosen for nuclear power due to its ease of splitting.
• Regulatory Approval: The criticality test was approved by India’s nuclear regulator, Atomic Energy Regulatory Board (AERB).

Significance

• Expansion of clean energy: The KAPP would serve several western states and provide clean and sustainable energy.
• Addresses excess thermal margins issue: KAPP addresses the excess thermal margin issues. 
  • Thermal margin’ is the extent to which the operating temperature of the reactor is below its maximum operating temperature.
• Improves indigenous Capability: Construction of KAPP marks the growth of indigenous capability and would lead the path towards future construction for the PHWRs.
• Safe Nuclear Plants: Installation of world-class safety features and implementing learnings from failures worldwide (such as the Fukushima Disaster) will make nuclear energy more reliable and safe.

Source: AIR