High-Energy Proton Accelerator System

Visakhapatnam has been selected as the site for a high-energy proton accelerator system that will support India’s long-term nuclear energy strategy, particularly its three-stage nuclear power programme and the utilisation of thorium resources through Accelerator-Driven Systems (ADS). The project is being developed by the Raja Ramanna Centre for Advanced Technology (RRCAT), Indore.

The location has been chosen because of its strong scientific and industrial ecosystem, along with its proximity to the sea, which ensures a reliable supply of cooling water required for high-energy nuclear and accelerator systems.

What is a High-Energy Proton Accelerator System?

A high-energy proton accelerator system is a scientific device that uses strong electromagnetic fields to accelerate protons (positively charged particles from hydrogen atoms) to extremely high speeds, forming a powerful proton beam.

This proton beam is then directed at a heavy metal target such as lead or bismuth. When the high-speed protons strike the target, they trigger a process called spallation, where the heavy nucleus breaks apart.

As a result of this reaction, a large number of neutrons are released, which can be used to sustain nuclear reactions in a controlled manner.

What is an Accelerator-Driven System (ADS)?

An Accelerator-Driven System (ADS) is a hybrid nuclear energy system that combines a proton accelerator with a sub-critical nuclear reactor.

In this system:

• The reactor core is designed to be sub-critical, meaning it cannot sustain a nuclear chain reaction on its own.

• It depends on an external supply of neutrons generated by the proton accelerator.

• The spallation reaction in the heavy metal target produces these neutrons, which then induce fission in the reactor core.

Why ADS is Important for India

1. Harnessing Thorium Resources

India has around 25% of the world’s thorium reserves, making thorium a strategic long-term energy resource.

However, Thorium-232 is not fissile, meaning it cannot directly sustain a nuclear chain reaction. It is a “fertile” material that must first absorb a neutron to convert into Uranium-233 (U-233), which is fissile and capable of producing energy.

The high neutron flux from ADS helps in this conversion process, enabling thorium to be effectively used as a fuel for electricity generation.

2. Nuclear Waste Reduction

Traditional nuclear reactors produce long-lived radioactive waste, including minor actinides that remain hazardous for thousands of years.

ADS technology can help address this problem through nuclear transmutation, where high-energy neutrons break down or convert these long-lived radioactive elements into shorter-lived or stable isotopes. This significantly reduces the long-term burden of nuclear waste management.

India’s Three-Stage Nuclear Power Programme

India’s Three-Stage Nuclear Power Programme is a long-term nuclear energy strategy designed to ensure energy security and sustainable electricity generation using the country’s limited uranium resources and abundant thorium reserves. The programme was conceptualised by Dr. Homi J. Bhabha, the pioneer of India’s nuclear science programme.The central idea is to gradually move from uranium-based reactors to a thorium-based fuel cycle, making India self-reliant in nuclear energy in the long run.

Objective of the Programme

The main objective of the programme is to use India’s uranium resources efficiently in the early stages and ultimately shift to thorium-based reactors.

India has limited uranium reserves but very large thorium deposits. Therefore, the programme is designed to first generate plutonium from uranium and then use it to develop a system that can finally utilise thorium for large-scale power generation.

Stage 1: Pressurised Heavy Water Reactors (PHWRs)

Purpose of Stage 1

The first stage focuses on generating electricity and simultaneously producing Plutonium-239 (Pu-239), which is essential for the next stage of the programme.

Working of Stage 1

In this stage, natural uranium is used as fuel. The uranium mainly contains Uranium-238, which does not directly sustain a chain reaction but helps in producing plutonium.

The reactors use heavy water (deuterium oxide) as both a moderator and coolant, which slows down neutrons and helps maintain the nuclear reaction efficiently.

Reactor Type

The reactors used in this stage are Pressurised Heavy Water Reactors (PHWRs).

Current Status

India has already developed and operated around 18 PHWRs, which form the backbone of its current nuclear power generation system. These reactors also produce Plutonium-239, which is crucial for Stage 2.

Stage 2: Fast Breeder Reactors (FBRs)

Purpose of Stage 2

The second stage aims to multiply nuclear fuel resources by breeding more fissile material than is consumed during operation.

Working of Stage 2

In this stage, Plutonium-239 and Uranium-238 are used as fuel in the form of mixed oxide fuel.

The reactor operates using fast neutrons, which allows Uranium-238 to absorb neutrons and convert into more Plutonium-239. This process is called “breeding”, as it creates more fuel than it consumes.

Reactor Type

The key technology used here is the Fast Breeder Reactor (FBR).

Current Status

The most important development in this stage is the Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, Tamil Nadu, which represents India’s transition toward advanced nuclear fuel efficiency.

Stage 3: Thorium-Based Reactors

Purpose of Stage 3

The third and final stage focuses on using India’s vast thorium reserves to achieve long-term and sustainable nuclear energy production.

Working of Stage 3

In this stage, Thorium-232 (a fertile material) is used instead of uranium.

Thorium itself cannot undergo fission directly. Instead, it absorbs neutrons and gets converted into Uranium-233, which is a fissile material capable of sustaining a nuclear chain reaction.

Reactor Type

This stage involves thorium-based reactors, including designs such as the Advanced Heavy Water Reactor (AHWR).

Current Status

This stage is still under research and development, but it is considered the most important long-term goal of India’s nuclear programme.

Raja Ramanna Centre for Advanced Technology (RRCAT)

The Raja Ramanna Centre for Advanced Technology (RRCAT), located in Indore, is a premier research institute under India’s Department of Atomic Energy.

Established in 1984, RRCAT focuses on:

• Particle accelerators

• Laser technology

• Synchrotron radiation research

It developed major national facilities such as Indus-1 and Indus-2 synchrotron radiation sources, which are used for advanced scientific research across disciplines.

RRCAT also contributes to applied technologies, including:

• Electron-beam sterilization of medical equipment

• Metal 3D printing innovations

• Optical fibre sensor systems

• Cryogenic cooling technologies for MRI machines

Conclusion

The proposed high-energy proton accelerator system in Visakhapatnam represents a significant step in India’s advanced nuclear research. By enabling Accelerator-Driven Systems, it aims to improve nuclear safety, support thorium utilization, and reduce radioactive waste.