7th July 2025 (11 Topics)
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700 MWe PHWRs at Kakrapar
Context:
India's nuclear energy programme achieved a key milestone as the AERB granted a five-year operational licence to NPCIL for Units 3 and 4 of Kakrapar Atomic Power Station—India's first indigenously developed 700 MWe PHWRs.
Pressurised Heavy Water Reactor (PHWR)
- A Pressurised Heavy Water Reactor (PHWR) is a nuclear reactor using natural uranium as fuel and heavy water (D?O) as both moderator and coolant.
- Heavy Water Role: Deuterium (²H) in heavy water slows down neutrons without absorbing them—essential for fission in natural uranium.
Key Technical Features
- Fuel: Natural uranium (U-238 and U-235); does not require enrichment.
- Moderator/Coolant: Heavy water (D?O) used for both neutron moderation and heat transfer.
- Design: Based on pressure tubes instead of a large pressure vessel (used in LWRs).
- Heat Transfer Mechanism: Fission heat is transferred to a secondary loop to generate steam and drive turbines.
Working Principle
- Chain Reaction: Neutrons are slowed by heavy water, enabling sustained fission in U-235.
- Heat Generation: Resultant heat is absorbed by circulating heavy water.
- Electricity Production: Heat is exchanged in a secondary circuit to produce steam for turbine-driven electricity generation.
Advantages of PHWRs
- Use of Natural Uranium: Avoids costs and logistics of uranium enrichment.
- Online Refueling Capability: Can be refueled without shutdown, increasing reactor uptime.
- Fuel Versatility: Can operate using MOX fuel or thorium, supporting India’s thorium-based energy roadmap.
- Economical Long-Term: Though heavy water is expensive, low fuel costs and efficient operation make it cost-effective over time.
Disadvantages
- Heavy Water Cost: High cost for production, storage, and maintenance.
- Design Complexity: Pressure tubes are prone to stress corrosion, requiring periodic inspection and replacement.
- Safety Challenges: Although robust, pressure tube rupture poses a safety concern if not properly managed.
Global Deployment
- India: Global leader in indigenous PHWR technology (e.g., Kakrapar 700 MWe reactors).
- Canada: Developer of the CANDU (CANada Deuterium Uranium) PHWR design.
- Other Countries: PHWR/CANDU variants used by Argentina, China, and South Korea.
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Atomic Energy Regulatory Board (AERB): Establishment & Legal Basis
Mandate and Functions
Scope of Regulatory Activities
Organisational Structure
o Safety Review Committee for Operating Plants (SARCOP) o Advisory Committee on Project Safety Review (ACPSR) o Radiological Safety Advisory Committee (RSAC)
Safety Code:
o Collaborates with IAEA (International Atomic Energy Agency). o Participates in global nuclear safety conventions like the Convention on Nuclear Safety (CNS). o Aligns Indian safety protocols with international best practices. |
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