Thorium and nuclear power: The longer fuel cycle

At Kalpakkam on 6 April 2026, the Prototype Fast Breeder Reactor sustained a controlled nuclear chain reaction for the first time. First criticality was a major engineering milestone for the 500 MWe reactor designed by the Indira Gandhi Centre for Atomic Research and built by BHAVINI. It brought a long-delayed project into a new phase of commissioning. [1]

The next stages still mattered. During a review on 27 June, officials examined low-power physics experiments and turbine-generator overhauling. The department said that turbine work was necessary before synchronising the reactor with the electricity grid. The April event therefore established criticality, rather than delivery of 500 MW of commercial power. [2]

A project across governments

The PFBR’s history predates 2014. A parliamentary committee recorded that the government approved it in September 2003, with completion originally due in September 2010. The deadline was subsequently revised more than once. Scientists, manufacturers and successive administrations contributed to a project whose eventual criticality came far beyond that original schedule. [3]

Its significance lies partly in what happens to the fuel. India’s three-stage programme was conceived near the beginning of its nuclear effort: natural uranium in pressurised heavy-water reactors supplies plutonium for fast breeders; a later stage is intended to use uranium-233 bred from thorium. The sequence seeks to stretch limited uranium resources and eventually draw on much larger thorium deposits. [4]

A fast breeder is a bridge in that sequence. It should not be described as proof that India has already established a commercial thorium-powered fleet.

Research and operating power

In July 2026, the Department of Atomic Energy described large-scale thorium utilisation as following the creation of adequate fast-breeder capacity. It reported work on reprocessing and fuel fabrication, including uranium-233 derived from irradiated thorium and made into fuel for the KAMINI research reactor. Molten-salt reactor materials and chemistry were also under development. [5]

BARC’s Advanced Heavy Water Reactor is another strand: a 300 MWe design intended to demonstrate thorium utilisation and advanced safety features. Its technical description establishes a design and research programme, rather than an operating commercial station. [6]

The wider nuclear fleet already supplies electricity. A separate July parliamentary reply put installed capacity at 8,780 MW across 24 plants and nuclear’s contribution to national electricity generation at about 3.1% in 2025–26. Its annexure includes the newer 700 MW units at Kakrapar and Rajasthan, alongside older reactors. [7]

The government’s 100 GW ambition for 2047 is much larger than that existing fleet. Its roadmap includes heavy-water reactors, light-water reactors and future breeders. Reaching it will require construction and commissioning on a different scale; at Kalpakkam, the June progress report was still concerned with the equipment and experiments needed to connect the first prototype to the grid. [7] [2]