Context:

• India’s 500 MWe indigenously developed Prototype Fast Breeder Reactor (PFBR), located at Kalpakkam in Tamil Nadu, has achieved criticality for the first time.

Key Points:

• This achievement marks India’s formal entry into the second stage of its three-stage nuclear program, envisioned by Dr. Homi Jehangir Bhabha.
• Chairman of the Atomic Energy Commission (AEC), Dr. Ajit Kumar Mohanty, also described it as a symbol of entering the second stage of Bhabha’s three-stage program.
• Prime Minister Narendra Modi termed it a “landmark step in India’s civil nuclear journey.”

Stage 1:

• Main Technology: PHWR (Pressurized Heavy Water Reactor)
• Fuel: Natural Uranium (contains only 0.7% U-235, rest is U-238)
• Moderator & Coolant: Heavy water is used, which efficiently slows down neutrons, enabling a chain reaction even with natural uranium.
• Advantage: Does not require expensive uranium enrichment.

Main Output of Stage 1 – Plutonium-239:

• U-238 absorbs neutrons and converts into Plutonium-239 (Pu-239).
• Spent fuel is reprocessed to extract plutonium, which is used in Stage 2 (PFBR).
• Most operational reactors in India (Kaiga, Kakrapar, Narora) are PHWRs.
• These are operated by Nuclear Power Corporation of India Limited (NPCIL).

Stage 2:

• Key Feature: Produces more fissile fuel than it consumes (breeder technology).
• Process: Uses Pu-239 from Stage 1 as fuel, surrounded by a blanket of U-238, which converts again into Pu-239 under neutron bombardment.

Key Features of PFBR (Kalpakkam):

• Fuel: Mixed Oxide (MOX) fuel (Plutonium dioxide + Uranium dioxide)
• Neutron Speed: No moderator is used, hence called a “fast” reactor.
• Coolant: Liquid sodium is used instead of water due to its high heat absorption capacity.

Stage 3:

• Final and most important stage of India’s nuclear program for long-term energy self-reliance.
• Fuel: Thorium-232 (not fissile), used with Uranium-233 (U-233) obtained from Stage 2.
• Breeder Technology: Produces more U-233, creating a sustainable fuel cycle.
• India holds ~25% of global thorium reserves (mainly in coastal sands of Kerala and Odisha).
• Energy Security: Can meet India’s electricity needs for 300–400 years.
• Safety: Thorium reactors produce less radioactive waste and are considered safer than uranium reactors.

Advanced Heavy Water Reactor (AHWR):

• Being developed for Stage 3.
• Indigenous design using the Thorium-U-233 fuel cycle for large-scale power generation.

Technical Features of the Reactor:

• Design & Construction: Designed by Indira Gandhi Centre for Atomic Research (IGCAR) and built by BHAVINI.
• Fast Breeder Technology: Produces more fuel (Pu-239) than it consumes.
• Fuel: MOX (Uranium-Plutonium mixed oxide) fuel.
• Coolant: Liquid sodium.

Strategic and Economic Significance:

• Global Position: India will become the second country after Russia to operate a commercial fast breeder reactor.
• Energy Security: Reduces dependence on uranium imports.
• Thorium Pathway: Lays foundation for utilizing India’s vast thorium reserves.
• Environment: Supports India’s Net Zero target by 2070.

Meaning of Criticality: A state where a self-sustaining nuclear fission chain reaction begins, essential for controlled power generation.

Types of Nuclear Reactors in India

1. Pressurized Heavy Water Reactor (PHWR):

• Uses natural uranium and heavy water as coolant and moderator.
• No enrichment required.
• Most operational reactors are PHWRs.

2. Pressurized Water Reactor (PWR):

• Uses high-pressure water as coolant and moderator.
• Transfers heat to a secondary loop for steam generation.
• Kudankulam reactors are PWRs (Russian design).

3. Boiling Water Reactor (BWR):

• Water boils directly in the core to produce steam.
• Tarapur has two operational BWR units.

4. Fast Breeder Reactor (FBR):

• Uses fast neutrons and liquid sodium coolant.
• Produces more fuel than it consumes.
• PFBR at Kalpakkam has achieved criticality.

5. Small Modular Reactor (SMR):

• Compact, factory-built modular reactors.
• Not yet operational in India; designs like BSNR-200 and SMR-55 under development.

6. Advanced Reactors:

• Includes high-temperature gas-cooled and molten salt reactors.
• Under research or conceptual stage in India.

Note: PHWRs are the backbone of India’s nuclear energy program.