UPSC Previous Year Question | Mains GS3 | 2026

Distinguish between a Fast Breeder Reactor (FBR) and a thermal nuclear reactor. In the context of the first indigenously developed prototype FBR at Kalpakkam, explain the term ‘criticality’. What are its implications for the clean energy future of our country? (150 words)

Answer

Introduction

A thermal reactor uses moderated neutrons to sustain fission; an FBR uses fast neutrons and produces more fissile material than it consumes.

Key Distinction

Thermal reactors generally use water moderation and uranium fuel, while an FBR uses a fast spectrum, liquid sodium coolant and a fuel cycle designed for breeding plutonium or U-233. The Kalpakkam prototype is part of India’s staged nuclear programme and greater utilisation of thorium resources.

Criticality

Criticality is the condition in which each fission generation produces exactly enough neutrons to sustain the next: k-effective equals one. Subcritical means the chain reaction declines; supercritical means it rises. It is a controlled operational state, not an accident.

Clean-Energy Implications

FBRs offer low operational emissions, high energy density, firm power and fuel-resource extension. Risks include capital cost, sodium reactivity, radioactive waste, proliferation and accident management. Independent regulation, passive safety, waste stewardship and public transparency are essential.

Keywords

science and technology; emerging technology; strategic application; India

Topics: emerging technology, india, science and technology, strategic application