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Small modular reactors may have climate benefits, but they can also be climate-vulnerable

Small modular reactors may have climate benefits, but they can also be climate-vulnerable
Photo: Shutterstock.

The nuclear power plants of the 20th century were, for the most part, enormous beasts. They cost many billions of dollars to build and needed a sizable and well-trained workforce to operate. Furthermore, with an energy output of about 1000 MWe per reactor being the norm, they required an extensive electricity grid capable of routinely consuming the huge amounts of energy that they produced. These characteristics have meant that large nuclear power plants have almost exclusively been built in industrialized countries.

More recently, a new class of small modular reactors (SMRs) for power generation have been gaining in popularity and are supposedly better suited for use in developing countries. SMRs hold the promise of driving progress towards universal access to modern energy sources and several other Sustainable Development Goals in a climate-friendly way. However, while they may not have a negative impact on future climate change, SMRs are not immune to the direct and indirect impacts of an already changing climate.

Great expectations on SMRs: A low-carbon energy transition for the developing world

SMRs have lower capital costs and shorter construction times than the reactors associated with traditional nuclear power plants. Having lower energy output, they can also work with lower-capacity grids. They can be sited in remote and less-developed areas and can even be retrofitted to existing infrastructure when coal-fired plants are decommissioned. The modular design means they can be easily built—and in time expanded—to match local power demand.

These characteristics—along with others, such as lower carbon emissions and lower fatality rates from accidents and pollution per unit of produced energy compared with many other energy sources—explain why dozens of states have expressed interest in building an SMR of some kind. According to data from the OECD’s Nuclear Energy Agency and the World Nuclear Association, at least 40 states are taking steps towards building an SMR on their territories.

The IAEA has counted at least 80 SMR designs. Most are intended to produce electricity for 60 years or more. With the time allowed for construction, decommissioning and potential extensions of operating life, it is conceivable that the lifetimes of future SMRs may approach 100 years or more.

The other side of the coin: SMRs and climate risks

A century is a long time. At any given location, political and societal changes are inevitable, many impossible to predict. The case of the Zaporizhzhia Nuclear Power Plant in Ukraine is a case in point: When the decision to build it was taken in 1977, the idea that it would be caught up in a conflict between a post-Soviet Russia and an independent Ukraine was virtually inconceivable.

Climate change and its direct and indirect effects, including on politics and security, also pose risks for nuclear power plants and other critical infrastructure. Direct effects include rapid-onset extreme weather events (such as storms and storm surges, heatwaves and flash floods) as well as slower-onset phenomena (such as sea-level rise, water scarcity, changes to rainfall or average temperatures). All of this can undermine the safe and secure functioning of nuclear facilities. For instance, drought—especially compounded by competing demands for water—could disrupt the cooling water supply to a reactor, potentially necessitating a shutdown, while floods or storms could damage critical systems.

A 2021 analysis of nuclear power plants’ vulnerability to such climate-linked effects is full of important insights. The study shows that the average frequency of climate-linked power outages at nuclear power plants globally has dramatically increased—from 0.2 outages per reactor-year in the 1990s to about 0.82 in 2000s, to 1.5 in 2010–19. It projects that energy losses due to climate change will continue to rise among the world’s nuclear power plants.

That study’s findings for the period 2010–19 suggest that, after hurricanes and typhoons (in the United States, South and South East Asia), the second largest climate-linked contributor to outages was increased ambient temperatures. Higher ambient temperatures can affect nuclear power plants in a variety of ways. For example, warmer temperatures can foster the rapid growth of algae or other biological material, which can in turn clog cooling water intakes, reducing production and even requiring the plant to shut down, particularly in warmer areas or reactors using seawater for cooling. High ambient temperatures can also make power generation less efficient. Many of the developing countries where electricity access is currently lowest (and thus where SMRs might have the greatest value in promoting development) already have relatively high ambient temperatures, which are likely to increase further.

As figure 1 shows, some of the states that have already announced interest in building SMRs are in areas highly exposed to the physical effects of climate change, including lower-middle income countries. Although the accident at the Fukushima Daiichi nuclear power plant in 2011 was caused by a natural disaster unrelated to climate change, it demonstrated that even in a wealthy, industrialized country like Japan, nuclear facilities can be vulnerable to extreme natural events.

Building SMRs for the long term

The current demand for SMRs suggests that the number of nuclear power plants operating worldwide is set to rise substantially, many of them in remote areas or in climate change-exposed countries where emergency response capacity and resources may be limited. The good news is that, with most SMRs still at the design stage, it should be possible to take climate-related risks into account in both technical features and eventual deployments. The most acute threats of extreme weather events to nuclear safety can be successfully addressed by shutting down the reactor until an event has passed. As SMRs are newer and smaller than traditional reactors, the risks sometimes associated with such shutdowns should be smaller. Also, greater resilience is being built into many new SMR designs, such as passive cooling systems and the possibility for underground installation. The IAEA has listed possible ways of adapting nuclear power plants to the different direct impacts of climate change, a selection of which are shown in table 1.

Numerous countries are enthusiastic about exercising their ‘inalienable right’ to the peaceful use of nuclear energy secured under the 1968 Nuclear Non-Proliferation Treaty (NPT), making it likely that a significant number of SMRs will be built. Governments and planners, along with regulatory bodies and the companies designing and delivering the SMRs, must consider how best to ensure a century of safe operation amid unpredictable risks, including—but by no means limited to—direct and indirect risks related to climate change.

However, the operation of any power plant, including an SMR, always presents some level of risk. A multi-parameter trade-off is inevitable between the right to peaceful use of nuclear power, along with its potential development and climate benefits, and the imperatives of nuclear non-proliferation, safety and security in an uncertain future.


Vitaly Fedchenko is a Senior Researcher in the SIPRI Weapons of Mass Destruction Programme.