Context: The fourth unit of the Kakrapar Atomic Power Project (KAPP-4) in Gujarat, with 700 MWe capacity, started controlled fission chain reaction and thus became critical.

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.

• A pressurized 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.

• These reactors are Pressurised 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 in the 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.

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.

• Kakrapar Atomic Power Project: The first criticality is the start of a controlled fission chain reaction.

• This is what KAPS-4 achieved. 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 Choice: 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).

Safety Features

• The Unit-3 and Unite 4 of KAPS have steel-lined inner containment systems that prevent any radioactive material from escaping in case of an accident.

• They also have passive decay heat removal systems which safely cool down the reactor even when it is shut down.

Significance

• Signifies a crucial step in the operational readiness of the nuclear power plant.

• Efficient and continuous production of electricity through nuclear fission.

What is the state of Nuclear Energy in India?

• In 2022-23, nuclear energy formed around 2.8 percent of India’s total energy production.

• NPCIL presently operates 23 reactors with a total capacity of 7,480 MW.

• With more projects under construction and accorded sanction, the existing nuclear power capacity is going to be increased to 22480 MW by the year 2031.

India’s Three-Stage Nuclear Power Programme

• India’s three-stage nuclear power programme was formulated by Homi Bhabha in the 1950s to secure the country’s long term energy independence, through the use of uranium and thorium reserves found in the monazite sands of coastal regions of South India.

• Stage 1- Pressurized heavy water reactor (PHWR): The first stage involved using natural uranium to fuel PHWR to produce electricity and Plutonium-239 as a byproduct.

• Also the byproduct plutonium-293 would be used in the second stage.

• Stage 2- Fast breeder reactor (FBR): The second stage involves using plutonium-239 to produce fuel, which would be used in Fast Breeder Reactors. Plutonium 239 undergoes fission to produce energy. Once a sufficient amount of plutonium-239 is built up, thorium will be used in the reactor, to produce Uranium-233. This uranium is crucial for the third stage.

• Stage 3- Advanced Heavy Water Reactor (AHWR): The main purpose of stage-3 is to achieve a sustainable nuclear fuel cycle.

• The advance nuclear system would be used a combination of Uranium-233 and Thorium.

• Thorium absorbs the neutrons, which can more efficiently produce more Plutonium in Fast Breeder Reactor for a faster growth.

• Thus, the ultimate objective of the above programme is to create capacity to use Thorium for sustainable production of nuclear energy and make India energy independent.