Q. Distinguish between a Fast Breeder Reactor (FBR) and a thermal nuclear reactor. In the context of first indigenously developed prototype FBR at Kalpakkam, explain the term ‘criticality’. What are its implications for clean energy future of our country?
Question from UPSC Mains 2026 GS3 Paper
Model Answer:
Core loading at the 500 MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam operationalizes Stage-II of India’s Three-Stage Nuclear Programme, accelerating the transition toward a closed fuel cycle.
Distinction: FBR vs. Thermal Reactor
| Parameter | Fast Breeder Reactor (FBR) | Thermal Nuclear Reactor (e.g., PHWR) |
|---|---|---|
| Neutron Energy | Fast neutrons (>0.1 MeV) | Slow/thermal neutrons (≈ 0.025 eV) |
| Moderator | None used | Heavy/Light water or Graphite required |
| Coolant | Liquid Sodium | Heavy water / Light water |
| Fuel Cycle | Breeds more fissile material (Pu-239) than it burns | Net consumer of fissile fuel (U-235) |
‘Criticality’ Explained
Criticality refers to the state where a nuclear fission chain reaction becomes self-sustaining—the neutron multiplication factor (keff) equals 1, ensuring stable, continuous power generation without external neutron injection.
Implications for Clean Energy Future
- Thorium Roadmap: Acts as the vital bridge to Stage-III by breeding fissile U-233 from vast domestic Thorium reserves.
- Waste & Fuel Efficiency: Multiplies energy extraction from uranium by >70× while incinerating long-lived minor actinides, minimizing radioactive waste.
- Firm Green Baseload: Supplies stable, round-the-clock clean electricity to balance intermittent solar-wind grids, supporting the Net-Zero 2070 target.
PFBR criticality cements indigenous technological mastery (BHAVINI), unlocking long-term energy security through sustainable, closed-loop nuclear power.
