एक द्रुत प्रजनक रिएक्टर (एफ बी आर) और एक तापीय परमाणुक रिएक्टर के बीच भेद बताइए। कल्पक्कम में स्वदेशी रूप से विकसित प्रथम प्रारूपी (प्रोटोटाइप) एफ बी आर के संदर्भ में, ‘क्रान्तिकता (क्रिटकलिटी)’ पद की व्याख्या कीजिये। हमारे देश के स्वच्छ ऊर्जा भविष्य के लिये इसके निहितार्थ क्या हैं ?
Read this question in English
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 ?
🧭 How to think about this question · directive: “distinguish / explain / what”
Decode the demand
- Three directives, three parts: 'distinguish' asks for a point-by-point contrast of FBR and thermal reactor; 'explain' asks what criticality means, tied to Kalpakkam; 'what are its implications' asks for effects on clean energy, both promise and limits.
- The event in one line: India's first indigenous 500 MWe Prototype Fast Breeder Reactor attained first criticality on 6 April 2026, opening stage two of the three-stage programme.
- The trap: writing a general essay on nuclear energy. Each part needs its own heading, and criticality must be defined in physics terms, not as 'a milestone'.
Think in a structure
- Open with the dated fact and the three-stage programme, then turn to the contrast.
- Distinction as a table: neutrons, fuel, coolant, with a point on breeding; the table saves words and shows the examiner you know the mechanism.
- Criticality as a flowchart: from core loading to grid, so the term sits inside the real sequence at Kalpakkam.
- Implications in dimensions: fuel security, thorium bridge, climate targets, self-reliance, then caveats, each with a verified number where one exists.
- End positively: a way forward and Bhabha's vision as the anchor, linking 100 GW by 2047 to net zero by 2070.
Facts checked at source (5)· open
- DAE confirmed that the PFBR reached first criticality — the start of a controlled fission chain reaction — on 6 April 2026.Department of Atomic Energy — PFBR attains first criticality (7 April 2026) ↗“the 500 MWe Prototype Fast Breeder Reactor (PFBR) has successfully attained first criticality (start of controlled fission chain reaction) on 6th April 2026”
- DAE explains that fast neutrons convert uranium-238 in the blanket into plutonium-239, so the reactor produces more fuel than it consumes.Department of Atomic Energy — PFBR attains first criticality (7 April 2026) ↗“Fast neutrons convert fertile Uranium-238 into fissile Plutonium-239, enabling the reactor to produce more fuel than it consumes.”
- The PFBR is designed to eventually carry thorium-232 in its blanket, which transmutes into uranium-233 to fuel the third stage.DAE — PFBR at Kalpakkam attains first criticality (April 2026) ↗“The reactor is designed to eventually use Thorium-232 in the blanket. Through transmutation, Thorium-232 will be converted into Uranium-233, which will fuel the third stage of India’s nuclear power p”
- Budget 2025-26 set a target of 100 GW of nuclear capacity by 2047.PIB backgrounder — Nuclear Energy Mission, Union Budget 2025-26 ↗“The government has set an ambitious target of 100 GW nuclear power capacity by 2047, positioning nuclear energy as a major pillar in India's energy mix.”
- The Nuclear Energy Mission carries ₹20,000 crore for small modular reactor R&D, aiming at five indigenous SMRs by 2033.PIB backgrounder — Nuclear Energy Mission, Union Budget 2025-26 ↗“The government has allocated ₹20,000 crore for this initiative, aiming to develop at least five indigenously designed and operational SMRs by 2033.”
Question: UPSC's CS (Main) 2026, GS Paper III — paper ↗. Guidance: Minimalist IAS, checked 8 Nov 2026 (how we verify). ·
Model answer· 423words · Minimalist IAS
On 6 April 2026 the 500 MWe Prototype Fast Breeder Reactor at Kalpakkam attained first criticality, the start of a controlled fission chain reaction. It opens stage two of Homi Bhabha's three-stage programme, and its value lies in how it differs from the thermal reactors India has run so far.
How an FBR differs from a thermal reactor
| Feature | Thermal reactor (PHWR) | Fast Breeder Reactor (PFBR) |
|---|---|---|
| Neutrons | slowed by a moderator, heavy water | fast, no moderator |
| Fuel | natural or enriched uranium | uranium-plutonium mixed oxide (MOX), uranium-238 blanket |
| Coolant | heavy water | liquid sodium; compact, high-power core |
- Breeding: fast neutrons convert fertile uranium-238 into fissile plutonium-239, so the PFBR produces more fuel than it consumes.
- Fuel use: a thermal reactor burns mainly the small uranium-235 fraction; a breeder taps abundant uranium-238, multiplying energy from the same ore.
'Criticality' at Kalpakkam
- Self-sustaining chain: a reactor is critical when each fission, on average, causes exactly one more; neutron production equals neutron loss.
- Three states: sub-critical, the chain dies out; critical, steady power; super-critical, power rises; control rods hold the balance.
- Fuel loaded in core
- Control rods withdrawn step by step
- Chain reaction self-sustaining: first criticality
- Power raised in stages
- Grid connection
- Why it matters: first criticality proves that fuel, sodium systems and design by IGCAR and BHAVINI work together; power now climbs under safety checks.
Implications for India's clean-energy future
- Fuel security: far better use of scarce uranium; the closed fuel cycle also leaves less long-lived waste to store.
- Thorium bridge: the blanket is designed to carry thorium-232, breeding uranium-233 for the third stage built on India's large thorium reserves.
- Climate goals: firm, low-carbon baseload that balances variable solar and wind, towards net zero by 2070 and 100 GW nuclear by 2047.
- Nuclear Energy Mission, Budget 2025-26: ₹20,000 crore for small modular reactors, five indigenous SMRs by 2033.
- Self-reliance: sodium-cooled fast-reactor technology mastered at home, a capability few countries hold.
- Caveats: sodium reacts violently with air and water, costs and delays were long, reprocessing capacity is thin, public acceptance must be earned.
Way forward
- Build in series: follow-on fast reactors at Kalpakkam on fixed timelines, applying the lessons of PFBR's delays.
- Close the cycle: expand reprocessing and MOX fabrication so bred plutonium returns as fuel rather than stockpile.
- Regulate openly: independent AERB oversight and plain-language safety communication on sodium risk to build local trust.
Criticality at Kalpakkam turns Bhabha's three-stage vision from paper into power; if fast reactors are now built on time, thorium can carry India from 100 GW in 2047 to net zero in 2070.
Prepared by Minimalist IAS to the answer standard of Shivam Singh (mentor, 7 years) · facts checked against official sources (how we verify) · updated 8 Nov 2026. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.
