India’s nuclear strategy has long rested on a three-stage programme, built around a basic constraint: the country has limited uranium but vast reserves of thorium. In the first stage, pressurised heavy water reactors (PHWRs) run on uranium to generate electricity and produce plutonium. The second stage uses this plutonium in fast breeder reactors to multiply fuel and prepare the ground for the final phase — thorium-based nuclear power, where thorium is converted into uranium-233 for long-term energy security.
Former Atomic Energy Commission chairman Anil Kakodkar, who is now Chancellor of the Homi Bhabha National Institute and Chairman of the Rajiv Gandhi Science & Technology Commission, tells Anil Sasi that with a large PHWR capacity now running on imported uranium, India can start producing uranium-233 by irradiating thorium alongside advanced fuels such as HALEU, accelerating the country’s path to energy independence.
To what extent does the scale up of our PHWR capacity now potentially offer an opportunity for faster transition to thorium-based nuclear power generation in India?
Transitioning to thorium based nuclear power generation in India is critical to our securing energy independence. This requires building sufficient inventory of fissile U233 (uranium233) through irradiation of thorium in thermal or fast nuclear reactors of relevant capacity. Since our assessed domestic uranium resources at the time when the three stage programme was formulated were very modest, the required irradiation capacity based on thermal reactors was not possible. Building such reactor capacity through fast reactors, which can multiply through breeding of fissile fuel, was thus essential. This was the basis of our three-stage programme which remains valid and relevant even today.
Now that we can access uranium from the international market, the thermal reactor capacity is on a growth path with the Nuclear Energy Mission targeting 100GWe nuclear power capacity with PHWRs constituting the bulk. This scale-up is clearly an opportunity to start producing fissile U233 at scale in PHWRs and enable a faster transition to thorium-based nuclear power generation in India.
It is indeed possible to have Thorium-HALEU based drop-in fuel for PHWR which would also lead to economic, safety and security benefits while efficiently converting thorium to U233. A win-win situation that can be uniquely delivered by PHWRs.
How important is the need for additional financial resources and new players in potentially scaling up PHWR capacity to 50-75 Gw (1Gw or giga watt is equivalent to 1000 mega watts)?
Scaling up PHWR capacity to 50-75 Gw by the target date of 2047 would require an average annual capacity addition of around 3 GWe, which would mean adding 5 to 8 reactors every year depending on the mix of 700 MWe and 220 MWe units. This clearly would require significant additional financial resources. Also, one would need many other players from public as well as private sector to be brought in with NPCIL (state-owned Nuclear Power Corporation of India Ltd.) playing the role of technology provider, capacity builder, facilitator and mentor while implementing its own programme. NPCIL has done this in the past for capacity building in Industry.
How important is the need to be able to achieve a self-sustaining thorium-based nuclear power generation capacity to convert essentially thorium into fissile uranium, given the limited uranium availability for breeding in fast breeder reactors?
How feasible is the possibility of launching the thorium phase without having to wait for build up of required fast reactor capacity as was envisaged in our 3-stage plan? As I’d mentioned earlier, this is critical for India’s energy independence. Our aim should be to be able to set up self-sustained power generation capacity, through Thorium Molten Salt Reactors (where energy comes from fission of U233 while an equal or slightly higher amount of U233 is also produced), at a level consistent with the needs of Vikasit Bharat (developed India). This requires large irradiation platforms in sufficient numbers for conversion of thorium to U233. (The) growing PHWR capacity that is coming up offers a practical and handy opportunity to get going towards our energy independence without having to wait for the build up of fast reactor capacity.
In this context, how do you see the centrality of PHWRs fueled with imported uranium helping in this conversion of thorium to fissile uranium through irradiation of thorium (along with HALEU)?
Conversion of thorium to fissile uranium at scale through irradiation of thorium was envisaged in FBRs to be developed in the second stage. While progress is being made with the second stage programme, its full scale deployment to constitute irradiation platform/s for conversion of thorium to U233 at scale is considerably delayed. Balance development work in Fast Reactor domain involves completion of oxide-fueled PFBR (prototype fast breeder reactor), constructing follow up FBRs, development and subsequent deployment of short doubling time metallic-fueled fast reactors for faster growth of fast reactor capacity, along with establishment of related aqueous- and pyro-nuclear recycle technologies.
Considering the time scale necessary for the remaining development, it is unlikely that fast reactor capacity required to produce U233 in quantities necessary to support thorium based power generation capacity capable of taking over from uranium based power generation at scale commensurate with the national energy needs, would be available at the relevant point in time. On the other hand, large PHWR capacity is coming up based on imported uranium. Having imported HALEU instead and irradiating it in PHWRs along with thorium would enable regaining the lost ground and switch on the thorium-uranium233 stage much earlier… This is a win-win situation that should not be missed.
Does the fast reactor development project also need to continue simultaneously?
Yes. Without a doubt. We are still on a development path and our energy requirements will continue to grow. Nuclear fuel breeding would be necessary to meet our emerging energy needs, at least till fusion energy arrives on the scene.
The Sustainable Harnessing and Advancement of Nuclear Energy for Transforming India (SHANTI) Act, 2025, opens up the possibility of more imported LWR-based nuclear projects. How do you view their potential?
I have always viewed imported LWRs as an additionality. Given our large and growing energy needs, and deficit in our implementation capability, such additionalities are helpful provided they are economically competitive and consistent with our nuclear fuel cycle policies.
Further we should prioritise our development effort for futuristic technologies needed for our country (metal fuel reactors, molten salt reactors, high temperature reactors, thorium fuel cycles etc. etc.) and leverage proven imported technologies ready for addressing current niche demands.
Estimates suggest that a 1,000 MW LWR would need about 25 tonnes of enriched fuel per year at 80% PLF. Given the fuel price of around $1.76 million per tonne, the fuel cost for an LWR plant would translate to around Rs. 350 crore per annum (at 1$ = Rs 80). Fuel estimates for PHWRs would perhaps be lower, given that it is natural uranium that is used instead of enriched uranium. Given these numbers, how do you see the trade-off in combining thorium with small amounts of enriched uranium in PHWRs and how much more viable is this proposition from a cost perspective?
In terms of mined uranium needed to support a given nuclear power generation capacity, PHWRs are more efficient compared to LWRs. Fuel fabrication and back-end fuel cycle costs in PHWR fueled with natural uranium would be higher on account of higher fuel throughput as the burn up is low. These costs would come down with the use of enrichment in PHWR fuel. Thorium leads to further economy, provided burn up is higher than a minimum threshold. Fueling cost (front end + back end) with HALEU-thorium fuel in PHWR works out to be lower than with natural uranium.
