Dr Anil Kakodkar, former Chairman of the Atomic Energy Commission and a world-renowned nuclear scientist, has played a significant role in every aspect of India’s nuclear energy development, particularly in the construction of pressurized heavy water reactors despite severe international restrictions. The PHWRs, which account for the bulk of India’s nuclear power installations, are now being discussed as the platform for developing India’s own ‘small modular reactors’, known as the ‘Bharat Small Reactor’ (BSR). Kakodkar, a champion of self-reliance, spoke to businessline about BSR development and the new type of fuel, ANEEL (Advanced Nuclear Energy for Enriched Life) — a concoction of high enriched uranium and thorium that is making waves in the nuclear energy sector. Excerpts from the conversation:
Today, everyone is talking about small modular reactors. The finance minister mentioned Bharat Small Reactors in her budget speech. Is the BSR the way forward for India’s nuclear energy?
India’s nuclear power requirements are very large and cannot be met by small reactors alone. Similar to solar power, where there are both rooftop and large-scale solar plants, nuclear energy also requires large reactors.
That said, finding sites is always a challenge. However, there are many retiring or retired coal power plant sites that make good brownfield locations for nuclear power plants.
There is a condition that SMRs must meet: there should be no anxiety among the public even if an accident occurs. It is unlikely that these sites will meet the Atomic Energy Regulatory Board (AERB) criteria for an ‘exclusion radius.’ For all our reactors, we have an exclusion zone with a one-kilometer radius, and there should be no large population or significant infrastructure within several kilometers. It is unlikely that these coal plant sites will meet these criteria, as when they were established, there were no such requirements for coal plants. Therefore, rather than imposing rigid siting criteria regarding population, we should design the reactors so that they do not require an exclusion radius beyond the plant boundary.
So, you need a particular kind of reactor based on passive safety principles. These are called integrally safe reactors, where cooling is achieved through natural circulation. There are a few designs of this kind. When we talk about SMRs for India, we are referring to that type of plant.
What kind of design changes would BSRs call for?
You can put a metallic liner on the inside, which will reduce the exclusion radius from one kilometer to half a kilometer. This will make it easier to find suitable sites. Initially, we can start with this approach and then look at further evolution.
We can start deploying the BSRs with the existing design with minimal changes, so there is no delay in their deployment. This can be done in a public-private partnership (PPP) mode within the framework of the Atomic Energy Act. After establishing standardized designs and setting up some units, further design changes for increased modularization can be introduced progressively.
India is the only country in the world that has actually been practicing with small reactors. The 220 MW unit falls within the definition of a small reactor. Thus, India has significant experience in setting up and operating small reactors, with a remarkable safety record—Kaiga-1 once set a world record. So, why can’t we build these reactors in a public-private partnership (PPP) within the framework of the current statutory provisions of the Atomic Energy Act? That is what the Bharat Small Reactor is designed to achieve.
How would we handle the fuel requirements?
That is very important. Pressurized Heavy Water Reactors (PHWRs) use natural uranium, which does not provide very high burnup. It offers a burnup of approximately 7,000 MW-days per ton. This means that spent fuel from PHWRs is significantly larger than that from a light water reactor of equivalent capacity. However, whether it is a heavy water reactor or a light water reactor, the requirement for natural uranium is almost similar—in fact, the heavy water reactor is slightly more efficient and requires a bit less natural uranium. In light water reactors, uranium is first enriched, allowing the fuel to deliver a much larger amount of energy. Consequently, the spent fuel from a light water reactor is less than that from a heavy water reactor.
This is acceptable for moderate capacities, but when considering hundreds of gigawatts, the quantity of spent fuel will be large, with significant cost implications. You must collect and store the spent fuel for a very long time, which adds to the overall cost.
How good is this new fuel, ANEEL, for BSRs?
The concept of ANEEL fuel is to use enriched uranium instead of natural uranium, with a higher level of enrichment than that used in light water reactors. (Enrichment increases the percentage of the fissile material, Uranium-235, in natural uranium, which consists mainly of Uranium-238.) For light water reactors (LWRs), the enrichment is up to 5 per cent. In fact, the earlier definition of ‘low enriched uranium’ was enrichment up to 20 per cent, though you can’t exceed 20 per cent due to proliferation concerns. However, light water reactors typically operate with enrichment up to only 5 per cent.
Advanced reactors are now on the table. They discuss enrichment beyond 5 per cent but below 20 per cent. This is still considered low-enriched uranium (LEU) but is referred to as High-Assay LEU (HALEU).
ANEEL fuel comes from the idea that we can use the right composition of HALEU and mix it with thorium. Such thorium-HALEU fuel in PHWRs will do wonders. First, it would provide a burnup comparable to LWRs, thereby reducing the quantity of spent fuel produced.
Second, there are other performance advantages. For example, the fuel made of thorium oxide and uranium oxide has higher thermal conductivity (the ability to conduct heat away) than plain uranium oxide fuel. Additionally, its melting point is higher because it contains thorium. Therefore, if you are generating a certain amount of power in the fuel bundle, the higher thermal conductivity allows you to dissipate the energy easily, resulting in a lower operating temperature compared to pure uranium. As a result, the margin between the operating temperature and the melting point is larger. This is recognized as an accident-tolerant feature.
Today, accident-tolerant fuels are being developed worldwide. An accident becomes severe when the fuel goes into a heat-up mode, and the cladding of the fuel, which is usually some kind of zirconium alloy, starts reacting with water. This is an energetic reaction—it liberates hydrogen and generates more heat, increasing the severity of the accident. However, if you prevent the temperatures from rising to such high levels, the severity of the accident can be controlled.
There is a lot of development work going on worldwide, more intensely in the US, focusing on the cladding of the fuel. When researchers looked at ANEEL fuel, they recognized it as having a larger safety margin and thus being accident-tolerant. Therefore, (a reactor using) ANEEL fuel will incorporate the benefits of research related to accident tolerance and will also have the added advantage of a higher temperature margin.
So, ANEEL fuel brings down the cost because of less spent fuel, lower fuel inventory, and higher safety.
This ANEEL fuel has to come from abroad, so that makes us still dependent on imports. Can ANEEL fuel be produced in India?
We have enrichment capacity in the country, but we are enriching on a small scale. To enrich up to the level of power reactor use, we don’t have the capacity. Also, we don’t have that much uranium in the country. So, if we have to import uranium, we might as well import enriched uranium (HALEU). We already have the Civil Nuclear Cooperation Agreement with the US (and HALEU can be imported under it). I am a champion of self-reliance. I feel that doing it in this mode will make us uranium-independent sooner by leveraging thorium.
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Published on September 2, 2024
https://www.thehindubusinessline.com/news/science/small-reactors-could-take-off-soon-says-former-aec-chairman-kakodkar/article68592977.ece
