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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.

Atomic Energy Regulatory Board (AERB):

Establishment & Legal Basis

Established: 15 November 1983.
Under: Atomic Energy Act, 1962.
Constituted by the Government of India to carry out regulatory and safety functions in the nuclear energy sector.
Administrative Control: Operates under the aegis of the Department of Atomic Energy (DAE), but functions independently in regulatory matters.

Mandate and Functions

Safety Oversight: Regulates the use of ionising radiation and nuclear energy for civilian applications.
Licensing Authority: Grants licenses for siting, construction, operation, and decommissioning of nuclear and radiation facilities in India.
Enforcement Power: Has authority to enforce compliance with safety standards and shut down facilities in case of violations.

Scope of Regulatory Activities

Nuclear Power Plants (NPPs): Safety regulation of design, construction, commissioning, and operation.
Radiation Facilities: Medical, industrial, and research usage of radiation sources (like X-ray units, cobalt therapy units).
Radiation Waste Management: Ensures safe disposal and containment of radioactive waste.
Transportation of Radioactive Material: Regulates packaging, transport, and handling of radioactive substances.

Organisational Structure

Chairperson: Appointed by the Government of India.
Committees and Advisory Bodies:
- Safety Review Committee for Operating Plants (SARCOP)
- Advisory Committee on Project Safety Review (ACPSR)
- Radiological Safety Advisory Committee (RSAC)
These bodies support AERB with expert reviews and audits.

Safety Code:

Safety Codes: Formulates and enforces safety codes, standards, and guidelines.
International Coordination:
- Collaborates with IAEA (International Atomic Energy Agency).
- Participates in global nuclear safety conventions like the Convention on Nuclear Safety (CNS).
- Aligns Indian safety protocols with international best practices.

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700 MWe PHWRs at Kakrapar

Pressurised Heavy Water Reactor (PHWR)

Key Technical Features

Working Principle

Advantages of PHWRs

Disadvantages

Global Deployment