An indigenous pressurised heavy water reactor under construction at Kakrapar, Gujarat, 2016.
| Photo Credit: Reetesh Chaurasia (CC BY-SA)
Bhabha Atomic Research Centre (BARC) researchers have reported that a new kind of nuclear fuel, touted for being able to allow India to take advantage of its vast thorium reserves, will not fit in the country’s three-stage programme and could entail expensive reactor redesigns.
The study was published in Current Science.
The composition the team evaluated is called HALEU-Thorium. It is the basis for “Advanced Nuclear Energy for Enriched Life”, or ANEEL, a fuel that the state-owned NTPC, Ltd. and the U.S.-based company Clean Core Thorium Energy are currently exploring.
India’s long-term nuclear energy plan has three stages. In the ongoing first stage, India is using pressurised heavy water reactors (PHWRs) using natural uranium. However, India has much less access to uranium than thorium, so the next two stages are designed to transition to using more thorium.
ANEEL mixes thorium with high-assay low-enriched uranium (HALEU), which contains uranium enriched to 5-20%. Its proponents have suggested ANEEL could be a “drop-in” in existing reactors, including PHWRs, allowing them to use thorium today.
The Indian government recently passed the SHANTI Act to allow private companies to help deploy such advanced technologies.
In the study, K.P. Singh, Amit Thakur, and Anurag Gupta used computer modelling to test how HALEU-Th would perform in India’s standard 220-MWe reactors.
The models suggested that when used in one go rather than as part of the three-stage plan, HALEU-Th stayed in the reactor longer than natural uranium and slightly enriched uranium. Specifically, HALEU-TH achieved a burn-up of 50 gigawatt-days per tonne (GWd/t), allowing the reactor to produce 7x less spent fuel for the same amount of electricity.
(Natural uranium contains only 0.7% uranium-235; the rest is mostly uranium-238, which can’t sustain a nuclear reaction. In HALEU, uranium-235 makes up 5-20%.
Thorium also can’t sustain a nuclear reaction. But when combined with HALEU, which releases neutrons when it fissions, thorium absorbs the neutrons to become uranium-233, which is an excellent fuel. As a result, the reactor ‘burns’ for longer with HALEU-Th than with natural uranium.
Where natural uranium has a burn-up of around 7 GWd/t, HALEU-Th has a burn-up of 50 GWd/t — i.e. 7x more energy. So to generate 1,000 units of electricity, a reactor with natural uranium must consume seven bundles of fuel where one with HALEU-Th must consume only one.)
Because the fuel lasted longer, the heavy machinery used to refuel the reactor could also face wear, the authors added.
However, they also identified signs that indicated HALEU-Th couldn’t be a drop-in replacement in existing reactors. As thorium absorbs neutrons more aggressively than uranium, the authors found the reactor’s current shutdown rods became around 26% less effective.
The shutdown rods are made of materials that ‘kill’ a nuclear reaction in the reactor by rapidly absorbing neutrons. But since thorium also absorbs neutrons well, except to keep the reaction going, the shutdown rods and thorium end up competing for neutrons.
So using the fuel could entail redesigning the reactor’s primary emergency shutdown systems.
The authors also said it would take 7-10 years of operation for a reactor to reach a stable state with HALEU-Th, during which it would produce less power and more unused fuel, which the authors wrote would impose “severe economic penalties”.
Finally, India’s second stage depends on plutonium produced in the first stage, whereas HALEU-Th produced almost 20x less plutonium than natural uranium.
The researchers suggested that if the goal is to improve uranium efficiency in the current fleet, ‘slightly enriched uranium’ — i.e. uranium with 1.1% more fissile content — is a better option that also demands fewer changes to reactors.
Published – March 10, 2026 07:30 am IST
