Indigenous pressurized water heavy water reactor under construction at Kakrapar, Gujarat, 2016. | Photo credit: Reetesh Chaurasia (CC BY-SA)
Researchers at the Bhabha Atomic Research Center (BARC) have announced that a new type of nuclear fuel, touted as allowing India to tap its vast thorium reserves, will not fit into the country’s three-phase program and could require costly reactor rebuilds.
The study was published in Contemporary science.
The compound the team evaluated is called HALEU-Thorium. It is the basis for “Advanced Nuclear Energy for Enriched Life” or ANEEL, the fuel that the state-owned NTPC, Ltd. and US company Clean Core Thorium Energy. currently researching.
India’s long-term nuclear power plan has three phases. In the ongoing first phase, India is using Pressurized Heavy Water Reactors (PHWR) using natural uranium. However, India has much less access to uranium than thorium, so the next two phases are designed to shift 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 that ANEEL could be a “plug” in existing reactors, including PHWRs, allowing them to use thorium today.
The Indian government recently passed the SHANTI Act, which allows private companies to help implement such advanced technologies.
In the study, KP Singh, Amit Thakur and Anurag Gupta used computer modeling to test how HALEU-Th would perform in India’s standard 220 MWe reactors.
The models suggested that when used as a one-off, rather than as part of a three-stage plan, HALEU-Th remained in the reactor longer than natural uranium and slightly enriched uranium. Specifically, HALEU-TH achieved a burn rate of 50 gigawatt days per ton (GWd/t), which allowed 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 will not sustain a nuclear reaction. In HALEU, uranium-235 makes up 5-20%.
Thorium also cannot sustain a nuclear reaction. But combined with HALEU, which releases neutrons when it fissions, thorium absorbs neutrons to become uranium-233, which is an excellent fuel. As a result, the reactor “burns” longer with HALEU-Th than with natural uranium.
Where natural uranium has a combustion of around 7 GWd/t, HALEU-Th has a combustion of 50 GWd/t — that is, 7 times more energy. So to produce 1000 units of electricity, a natural uranium reactor must consume seven fuel bundles, while a HALEU-Th reactor must consume only one.)
Because the fuel lasted longer, the heavy machinery used to refuel the reactor may also have faced wear and tear, the authors added.
However, they also found signs that indicated that HALEU-Th could not be a drop-in replacement in existing reactors. Because thorium absorbs neutrons more aggressively than uranium, the authors found that current reactor shutdown rods are 26% less efficient.
The trip rods are made of materials that “kill” the nuclear reaction in the reactor by rapidly absorbing neutrons. But since thorium also absorbs neutrons well, in addition to sustaining the reaction, the closure rod and thorium end up competing for neutrons.
The use of the fuel could therefore mean redesigning the reactor’s primary emergency shutdown systems.
The authors also stated that the reactor would take 7–10 years of operation to reach a steady state with HALEU-Th, during which it would produce less power and more waste fuel, which the authors say would entail “severe economic penalties”.
Finally, India’s second stage depends on plutonium produced in the first stage, while HALEU-Th produced almost 20x less plutonium than natural uranium.
The researchers suggested that if the goal is to improve the efficiency of the uranium in the current fleet, “low-enriched uranium”—that is, uranium with 1.1% higher fission content—is a better option, which also requires fewer changes to the reactors.
Published – 10 March 2026 07:30 IST
