In News:

• India has selected Visakhapatnam, Andhra Pradesh, as the site for establishing a high-energy proton accelerator system to support its long-term nuclear energy strategy.
• The project will play a crucial role in advancing the Accelerator-Driven System (ADS) technology, which is central to India’s effort to utilise its vast thorium reserves and enhance nuclear safety.
• The initiative is being developed by the Raja Ramanna Centre for Advanced Technology (RRCAT) located in Indore, Madhya Pradesh.
• Visakhapatnam was chosen because of its strong technological ecosystem, availability of research infrastructure, and proximity to the sea, which ensures sufficient cooling water for operating high-energy accelerator systems.

High-Energy Proton Accelerator System

A high-energy proton accelerator is a scientific device that uses electromagnetic fields to accelerate protons (positively charged particles from ionised hydrogen) to extremely high speeds. The accelerated protons form a powerful proton beam that is directed toward a heavy metal target such as lead or bismuth.

When the high-speed protons collide with the heavy metal nucleus, a process known as spallation occurs. In this reaction:

• The heavy nucleus breaks apart due to the impact.
• A large number of high-energy neutrons are released.
• These neutrons can then be used to initiate nuclear fission reactions in a reactor system.

Thus, the proton accelerator becomes an external source of neutrons required for controlled nuclear reactions.

Accelerator-Driven System (ADS)

The Accelerator-Driven System is a nuclear reactor concept in which the neutron supply required for fission is provided externally by a proton accelerator.

Key features of ADS include:

• The reactor core remains sub-critical, meaning it cannot sustain a chain reaction independently.
• The spallation neutrons generated by the proton accelerator are injected into the reactor core to maintain fission.
• If the accelerator stops functioning due to a power outage or malfunction, the neutron supply ceases immediately.

This design provides high inherent safety, as the nuclear reaction automatically stops without external intervention, significantly reducing the risk of reactor meltdown.

Role of ADS in India’s Three-Stage Nuclear Programme

• India’s nuclear energy strategy follows a three-stage programme aimed at maximising the utilisation of its limited uranium resources and abundant thorium deposits.
• ADS technology supports the third stage of this programme, which focuses on thorium-based nuclear energy.

Harnessing Thorium Resources

India possesses around 25% of the world’s thorium reserves, primarily in monazite sands along its coastal regions. However, naturally occurring Thorium-232 is fertile rather than fissile, meaning it cannot directly sustain a nuclear chain reaction.

For thorium to become a usable nuclear fuel:

1. Thorium-232 must absorb a neutron.
2. It undergoes nuclear transformation (transmutation).
3. It converts into Uranium-233, which is a highly fissile material capable of sustaining nuclear reactions.

The high-energy neutrons generated by the ADS system are particularly effective in facilitating this conversion, enabling thorium to become a viable fuel for large-scale electricity generation.

Nuclear Waste Management

Another major advantage of ADS technology lies in nuclear waste transmutation.

Conventional nuclear reactors generate long-lived radioactive waste, including minor actinides, which remain hazardous for thousands of years. ADS systems can use high-energy neutrons to:

• Break down long-lived radioactive isotopes
• Convert them into shorter-lived or stable elements

This process significantly reduces the toxicity and storage duration of nuclear waste, thereby addressing one of the major environmental concerns associated with nuclear power.