Can small nuclear reactors solve India’s big energy challenge?

India is the third-largest energy producer globally, generating nearly 75 per cent of this energy from coal-fired power plants. As climate change concerns escalate and Himalayan glaciers vanish rapidly, India is exploring multiple avenues to decarbonise its economy.

Solar and wind power sources have quickly grown, fuelled by government incentives and public interest. Yet these renewable energies are inherently intermittent and unsuitable to meet base load requirements—the minimum amount of power needed to keep the electricity grid running smoothly throughout the day. Traditional sources like coal, nuclear, and hydroelectric plants fulfil this base load, while renewables and natural gas-fired plants typically cater to peak or variable loads.

India has pledged to reach net zero carbon emissions by 2070 at the COP26 climate conference in Glasgow in 2021, but the pathway to achieve this is unclear. India's economic growth depends on the availability of cheap electricity, the bulk of which comes from coal-fired plants. Reducing the dependence on coal is the most pressing challenge facing policymakers today.

One of the options under review is the phased retirement of ageing coal thermal power plants in favour of small modular nuclear reactors (SMRs). SMRs have power outputs ranging from 30 to 300 MWe, compared to their larger counterparts, typically rated at 1000 MWe or more. Because of their compact design, they can be built in smaller sites. They also do not require as much cooling water as large plants.

The advanced safety features of SMRs mean that an exclusion zone of 1.5 km around them, as currently mandated by the regulators in India, may not be necessary. Relaxing this rule could allow the dismantling of old coal-fired plants and the construction of SMRs in the same locations, thereby significantly reducing the time and complexities of acquiring new land sites.

Furthermore, designers claim that SMRs can be partially assembled in factories before being shipped to their final installation location, minimising the quantum of work needed on-site. This innovative construction method can enable new plants to come online within three years, a stark contrast to the decade-plus timelines typical of constructing large reactors. The feasibility of this claim is not yet known. The weight of an assembled plant will be in the range of 1000 tons, which rules out road transport. Transportation by sea or inland waterways may be feasible depending on the factory's location and the proposed site.

There has been a lot of excitement over the growth of nuclear power via the SMR route in the last two decades or so. Over eighty SMR designs have been conceived and studied globally, yet only two have been successfully built and connected to the power grid.

Russia has modified its KLT-40 pressurised water reactors (PWRs) used on icebreakers to construct two operational reactors aboard a power barge named Akademik Lomonosov. These reactors are rated for 35 MWe and were connected to the grid in 2022. Beyond electricity, these reactors can provide steam for domestic heating and facilitate freshwater production.

This marine PWR has a proven design and extensive operating experience. Its main drawback is that its capital cost is high. The Russians use it to provide power to the remote regions of Chukotka in Russia's Far East, where it is challenging to provide fuel for a conventional power plant. India has similar requirements in the Andaman and Nicobar Islands and Lakshwadeep.

For example, more than 50 diesel generators provide electricity to the four inhabited islands of Lakshwadeep. The peak load is about 30 MWe. A power barge like the Akademik Lomonosov can comfortably meet this requirement with zero emissions.

China has recently built a generation IV high-temperature gas-cooled reactor, the HTR-PM, that began operation in 2021 and was connected to the grid in 2023. Hot helium gas from two reactors feeds a single gas turbine for a total power output of 210 MWe.

This design is based on the German AVR and THTR-300 designs. A distinguishing feature of this reactor is its fuel, which is embedded in graphite pebbles the size of billiard balls, enhancing its proliferation resistance and allowing operation at significantly higher temperatures than traditional PWRs. Additionally, this reactor design ensures it can shut down safely in the unlikely event of a complete failure of supporting machinery. Time will tell if this reactor can be built and operated more economically than the PWRs.

The SMR field is rife with competing designs, and predicting the frontrunner in this evolving race would be premature. A historical parallel can be drawn to the 1940s and 1950s when research groups developed many reactor designs. Eventually, light water reactors (LWRs)—the scaled-up versions of submarine reactors—emerged as the dominant technology in subsequent power generation installations.

Today, research is focusing on scaling down and making compact and economical versions of the proven large reactor designs. Yet, significant questions linger regarding the wisdom of this shift from large reactors to SMRs. To place the energy situation into context, energy demand in metropolises like Delhi surpasses 8000 MWe, while Mumbai's demand exceeds 4000 MWe. This requirement will inevitably increase every year. How can SMRs, with their relatively modest outputs of 50 or 100 MWe, make a meaningful impact on meeting such overwhelming demands?

This leads to a critical consideration: should India allocate its limited capital resources, engineering expertise, and labour toward developing SMRs instead of investing in larger reactors and rapidly increasing the share of clean energy in the overall energy mix?

(The author is a nuclear engineer who has worked for many years in India’s strategic submarine program. He is currently working as the Director of the School of Engineering at DY Patil International University, Akurdi, Pune)