Context
- Recently, the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Chennai, achieved “criticality,” marking a historic leap in India’s civil nuclear journey. This milestone signifies that the nuclear fission chain reaction within the reactor has become self-sustaining and controlled.
- Developed by Bharatiya Nabhikiya Vidyut Nigam Limited (BHAVINI), the PFBR serves as the essential bridge to the second stage of India’s nuclear programme, paving the way for the eventual utilization of thorium for long-term energy security.
1. The Prototype Fast Breeder Reactor (PFBR)
- Location: Kalpakkam, Tamil Nadu.
- Capacity: 500 MWe (Megawatt electrical).
- Agency: Designed by Indira Gandhi Centre for Atomic Research (IGCAR) and built by BHAVINI.
- Fuel: Uses Mixed Oxide (MOX) fuel, which is a combination of Plutonium-239 (derived from Stage 1) and depleted Uranium-238.
- Coolant: Uses Liquid Sodium. Unlike water, sodium does not slow down neutrons, which is necessary for a “fast” reactor.
2. The “Breeder” Concept
- A breeder reactor is designed to produce more fissile material than it consumes.
- In the PFBR, neutrons trigger fission in Plutonium-239 to produce energy. Simultaneously, these “fast” neutrons convert the surrounding Uranium-238 (blanket) into more Plutonium-239.
- In the future, a Thorium-232 blanket will be used to breed Uranium-233, which is the fuel for the third stage.
3. India’s Three-Stage Nuclear Programme
The programme was formulated by Dr. Homi J. Bhabha to make India self-reliant by utilizing its modest uranium and vast thorium reserves.
| Stage | Reactor Type | Fuel Used | Key By-product/Goal |
| Stage 1 | Pressurised Heavy Water Reactor (PHWR) | Natural Uranium | Plutonium-239 |
| Stage 2 | Fast Breeder Reactor (FBR) | MOX (Pu-239 + U-238) | More Pu-239 / U-233 |
| Stage 3 | Advanced Heavy Water Reactor (AHWR) | Thorium-232 + U-233 | Energy from Thorium |
4. Technical and Safety Features
- Pool-type Reactor: The entire primary circuit (core, pumps, and heat exchangers) is immersed in a large pool of liquid sodium, providing high thermal inertia (safety against overheating).
- Closed Fuel Cycle: The Demonstration Fast Reactor Fuel Reprocessing Plant (DFRP) at Kalpakkam is designed to “close” the loop by reprocessing spent fuel from the FBR to extract plutonium and unburnt uranium.
- Liquid Sodium Challenge: Sodium is highly reactive with air and water; hence, the reactor requires sophisticated leak-detection and intermediate cooling loops.
Q. With reference to the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, consider the following statements:
1. It utilizes liquid sodium as a coolant because sodium does not moderate (slow down) neutrons.
2. The reactor is designed to function as a "bridge" to Stage 3 by producing Uranium-233 from a Thorium blanket.
3. Unlike the first-stage PHWRs, the PFBR operates on a closed fuel cycle where spent fuel is reprocessed.
How many of the above statements are correct?
(a) Only one
(b) Only two
(c) All three
(d) None
Answer: (c) All three
Solution:
STATEMENT 1 IS CORRECT: Fast breeder reactors require "fast" neutrons to sustain the breeding process. Sodium is a heavy atom compared to hydrogen (in water) and does not slow down neutrons significantly.
STATEMENT 2 IS CORRECT: The PFBR will eventually use Thorium-232 in its blanket to breed Uranium-233, which is the essential fissile material for the third stage of the nuclear programme.
STATEMENT 3 IS CORRECT: Stage 2 is explicitly based on a closed fuel cycle. The spent fuel is reprocessed at the onsite DFRP to recover plutonium for further use, unlike the "once-through" cycle often used in some older reactor designs.
