Nuclear reactors are devices used to initiate and control nuclear chain reactions to generate energy. They are primarily used for electricity generation, but they also have applications in research, medicine, and naval propulsion (such as in submarines and aircraft carriers).

1. Pressurized Water Reactor (PWR) - The most common type, using water under high pressure to prevent boiling.
2. Boiling Water Reactor (BWR) - Uses water as both a coolant and a steam source for turbines.
3. Pressurized Heavy Water Reactor (PHWR) - Uses heavy water (deuterium oxide) as a moderator and coolant, such as India's CANDU-based PHWRs.
4. Gas-Cooled Reactor (GCR) - Uses gas (like CO₂ or helium) as a coolant.
5. Fast Breeder Reactor (FBR) - Generates more fissile material than it consumes.
6. Molten Salt Reactor (MSR) - Uses liquid fuel mixed with molten salt, offering safety advantages.
7. Small Modular Reactors (SMR) - Compact reactors designed for flexibility and safety.

• Fuel (Uranium-235, Plutonium-239, or Thorium-232)
• Moderator (Slows down neutrons, e.g., water, graphite, or heavy water)
• Control Rods (Absorb neutrons to control the reaction, e.g., made of cadmium or boron)
• Coolant (Transfers heat, e.g., water, gas, or liquid metal)
• Containment Structure (Prevents radiation leaks)

High energy output
Low greenhouse gas emissions
Reliable power supply

 Radioactive waste disposal
 High initial costs
 Risk of accidents (e.g., Chernobyl, Fukushima)

India operates several types of nuclear reactors for electricity generation, research, and other applications. The country's nuclear program is largely based on Pressurized Heavy Water Reactors (PHWRs) but also includes other reactor types.

Types of Nuclear Reactors in India

1. Pressurized Heavy Water Reactor (PHWR) - Indigenous & Most Common

• Uses natural uranium as fuel and heavy water (D₂O) as both moderator and coolant.
• Majority of India's nuclear power plants use PHWRs due to abundant thorium reserves.
• Examples: Kakrapar, Tarapur, Rawatbhata, Narora, Kaiga, Kudankulam (future PHWRs planned).

2. Light Water Reactor (LWR) - Imported from Russia

• Uses enriched uranium as fuel and light water as coolant and moderator.
• Subtypes:
• Pressurized Water Reactor (PWR) - Used in Kudankulam Nuclear Power Plant (Russian VVER-1000 reactors).
• Boiling Water Reactor (BWR) - Used in Tarapur Atomic Power Station (TAPS-1 & 2, U.S.-supplied).

3. Fast Breeder Reactor (FBR) - Under Development

• Uses plutonium-239 & uranium -238 to generate more fissile material than it consumes.
• India's Prototype Fast Breeder Reactor (PFBR) is under construction at Kalpakkam as part of the three-stage nuclear program.

4. Advanced Heavy Water Reactor (AHWR) - Future Thorium Reactor

• Designed to use thorium-232 as a fuel, which is abundant in India.
• Developed at Bhabha Atomic Research Centre (BARC) for long-term energy sustainability.
• Yet to be commercially deployed.

5. Research Reactors

• Used for medical isotope production, research, and training.
• Examples:
• Apsara-U - India's first and upgraded research reactor at BARC.
• Dhruva - Indigenous research reactor for neutron research.
• KAMINI - The only reactor in the world using Uranium-233, built at IGCAR, Kalpakkam.

1. Stage 1 - PHWRs (Natural Uranium & Heavy Water)
   • Generates plutonium for the next stage.
2. Stage 2 - Fast Breeder Reactors (Plutonium & Uranium-238)
   • Produces more plutonium and some uranium-233.
3. Stage 3 - Thorium Reactors (Uranium-233 & Thorium-232)
   • Long-term goal for self-sufficient nuclear energy.