When I decided to write my PhD thesis on the history of the nuclear Rhine in the summer of 2018, the front pages of the newspapers were dominated by news of the record summer and that several nuclear power plants on the Rhine had to be shut down. Headlines focused on the topics of the low water level of the Rhine and to what extent the use of cooling water can affect flora and fauna, but also the danger posed by a lack of cooling water for the operation of nuclear power plants. By then, I had already planned to take a closer look at the effects of heat waves on the operation of nuclear power plants. In the course of my research, I found out that while heat waves are a problem, the thermal load on water bodies caused by the recirculation of cooling water is an equally pressing issue.
The Rhine River basin is, in relation to its flow per watershed, the most thermally polluted river basin globally mainly due to nuclear power plants. Thermoelectric power plants such as coal and nuclear power plants are major drivers of thermal pollution. Even though the European Union has set a limit of three degrees Celsius, the limit is exceeded by five degrees Celsius every year. The majority of thermal excess heat comes from nuclear and coal power plants that were built in the 1970s and 1980s.
At the end of the 1960s, a planning boom began in the countries along the Rhine. Switzerland was one of the countries that wanted to roll out nuclear power in a big way and even slowly turned away from its role as the pioneer of hydropower. In addition, Germany and France also wanted to use the water resources of the Rhine for cooling purposes, which quickly led to conflicts on the fair distribution of cooling water. Switzerland, France, Germany, and the Netherlands planned to build roughly around twenty-five nuclear power plants in the Rhine River basin (including the Aare and the Moselle), which would have made the Rhine one of the most nuclearized river basins in the world. Especially problematic was that energy companies were tempted to build nuclear power plants without external cooling systems as experts deemed the water resources of the Rhine to be sufficient.
In Germany, nuclear accidents hardly played a role in the early risk perception of the 1950s, 60s, and 70s. This is because the broad public knowledge about the extreme effects of a nuclear accident was almost non-existent. Instead, the focus was on the immediate effects of nuclear power plants that were unavoidable during operation, such as thermal pollution of water bodies. It was also in these early years that water management authorities were the most vocal administrative opponents of nuclear energy. Political supporters of nuclear energy tried to counteract the opposition by handing over water competences to the Federal Ministry of Atomic Energy. However, this decision did not lead to the desired decrease in criticism. In the 1970s, criticism regarding water became even louder when it came to the thermal pollution of the Rhine and the Weser.
Apart from environmentalists and the local population, countries like the Netherlands, being geographically disadvantaged and on the receiving end of the Rhine, also feared the excessive nuclear development on the Rhine River. This fear stemmed from the worrying potential impacts thermal pollution could have on drinking water supply. Experts especially worried that the Rhine would turn into a sewer as the oxygen level and the assimilative capacity of a body of water is affected when it heats up.
The discussion from the early years of nuclear energy seems at first glance to be a debate of the past. Therefore, it is worth looking at the actual problems of nuclear impacts on rivers, which are still evident today. We are talking about two independent yet also interdependent problems here. On the one hand, there is thermal pollution, which has been an issue since the early days of nuclear development. On the other hand, there is climate change, which affects aquatic bodies like rivers, but also nuclear power plants and is now a more pressing issue ever since. Due to temperature limits, heated cooling water can only turn into an aquatic body to a certain limit. As thermal pollution travels, this also affects the cooling capacity of industry as well as nuclear power plants downstream. In a warming climate, the cooling capacity is further reduced. And, in the case of low water levels, even more so.
Climate change scenarios predict that there will be more extreme weather events and that higher air temperatures will also lead to higher water temperatures. As the number of days with water temperatures above twenty-five degrees Celsius is expected to double, the International Commission for the Protection of the Rhine (ICPR) urges that water management measures be adapted to future conditions. Shutting down nuclear power plants in Germany led to observations of improvement, or lowering, of water temperatures.
Looking at historical documents, one might expect historical discussions of thermal pollution to resurface during times of climate change, recurring heat waves, and dangerously low water levels on the Rhine. However, within the debate on nuclear power’s role in the fight against climate change, thermal pollution does not get the attention it should. Professor of History of Technology at KTH Royal Institute of Technology Per Högselius recently opened up Pandora’s box with his opinion piece in the Swedish newspaper Dagens Nyheter, arguing that nuclear energy will become less and less predictable in the future. Nine nuclear engineers wrote a reply arguing that the nuclear energy industry is already calculating with climate change and that nuclear energy is still one of the most reliable energy suppliers.
The question at stake remains whether nuclear critics are overestimating the issue of a heating climate, if nuclear engineers are downplaying the problem by communicating that everything is under control—or if the truth is somewhere in the middle. A look at history shows that the nuclear industry has always liked to emphasise that all contingencies are under control and that maximum safety measures are in place. Although I would like to place trust in such statements, the accidents at Three Mile Island, Chernobyl, and Fukushima have spoken a different language. Moreover, there has always been a certain hubris of nuclear proponents towards the critical population that doubted absolute safety. Criticism was either refuted at all costs or critics were accused of not understanding the subject matter and not grasping the actual risks.
Not much has changed since the 1980s, as studies on nuclear power’s potential for a warming climate continuously speak a similar language. For example, Berger et al. address risk perceptions of the public in their study, but they still conclude that opposition to nuclear power stems from a lack of knowledge regarding the actual risks of nuclear energy. Some nuclear engineers themselves criticize this simplistic perspective on the interactions between society and the field of nuclear engineering, and they argue for a greater awareness of ethical responsibility in their field.
The ICPR writes in their adaptation strategy to climate change that sufficient knowledge is now available to make predictions regarding the impacts of climate change on the Rhine River system, and that predictable increases in temperature render nuclear power an unwise option. Contradictory to the position of the ICPR, the Intergovernmental Panel on Climate Change highlights in their 2018 special report that, according to most of the scenarios, primary energy will come from nuclear power and renewable energy by 2050. Other studies also suggest nuclear power may play a significant role in mitigating greenhouse gases. Scientists and researchers do not fully agree on the role of nuclear power for combating climate change. Some scientists advocate for implementing nuclear power into a future energy system. Arguing that nuclear power is the answer to climate change. Others conclude that increased development of nuclear energy from 2020 onwards will contribute sustainably to stabilizing global temperatures by 2100.
In studies on the suitability of nuclear power for fighting climate change, major risks such as nuclear waste storage, core meltdowns, or terrorist attacks are being addressed, but so-called “minor” risks such as thermal pollution are often being neglected. Statistics on the frequency of incidents and accidents worldwide are also difficult to acquire, as the International Atomic Energy Agency (IAEA) does not make this data publicly available over a long period. Additionally, other scientists highlight that nuclear power has proven to be too expensive and too often not rolled out quickly enough. These scientists argue that nuclear power is very unlikely to contribute to lowering greenhouse gas emissions, despite the optimistic projections of studies in favor of nuclear power.
The European Commission specifically addresses the issue of climate change as a danger for nuclear power generation. Heightened water temperatures and heat waves pose a particular threat as environmental regulation demands that nuclear power generation is cut back or even stopped when temperatures rise. Critics also argue that we cannot rely on mitigating climate change and that we should calculate with two degrees Celsius global warming. Anticipating our constraints concerning limiting global warming turns the effects of a changing climate on electricity production in general—and nuclear power plants in particular—into a far more urgent issue.
The past few years have shown that these hot periods are becoming more frequent as demonstrated in the UK in 2003, 2006, 2013, and 2018 or in France in 2019. In the most recent hot summer of 2022, it became obvious that nuclear power plants continue to have problems in unusually hot weather. Scientists have furthermore shown that the heat waves across the planet (and even in Siberia) in the last few years would not have been possible without human contribution to the changing climate. In Western Europe, interest in nuclear power plants is visibly decreasing. Nevertheless, even if countries like Germany or Switzerland decide to opt-out of nuclear, it does not mean they lower the risk within their own territory. Nuclear power plants are often built close to borders, such as on transboundary water courses like the Rhine.
Contemporary and historic debates about the promises and perils of nuclear power hinge on the issue of resilience. Are nuclear power plants resilient enough to cope with a changing climate, or will their immense water requirements and heat emissions contribute to the warming of water bodies and subsequently put more stress on the environment? It is about time that the neglected water risks get the attention they once received in the 1950, 60s and 70s. Through my historical research, I aim to revive forgotten discussions and to constructively contribute to the current debate on nuclear energy in times of climate change.
 Raptis, C., van Vliet, M. & Pfister, S. (2016). Global Thermal Pollution of Rivers from Thermoelectric Power Plants. Environmental Research Letters, (11); Raptis, C. E. & Pfister, S. (2016). Global freshwater thermal emissions from steam-electric power plants with once-through cooling systems. Energy, 97, pp. 46–57.
 Klaentschi, M. J. (1965). Standortprobleme von Kernkraftwerken in der Schweiz. Schweizerische Bauzeitung, 83(31), pp. 541–544; Nelkin, D. & Pollak, M. (1981). The Atom Besieged: Extraparliamentary Dissent in France and Germany. Cambridge: The MIT Press; Michaelis, H. (1982). Handbuch Kernenergie. Band 1. München: Deutscher Taschenbuch Verlag; Boos, S. (1999). Strahlende Schweiz. Handbuch zur Atomwirtschaft. Zurich: Rotpunktverlag; Hecht, G. (2009). The Radiance of France. Nuclear Power and National Identity after World War II. Cambridge: Massachusetts Institute of Technology.
 Radkau, J. (1980). Die Kernenergie-Kontroverse als eigentliche und uneigentliche Diskussion: Zum historischen Zusammenhang von kerntechnischer Entwicklung und Anti-AKW-Bewegung.
 Der Spiegel (1970). Tod im Strom. Der Spiegel, 23 February 1970, p. 46.
 ICPR (2015). Strategy for the IRBD Rhine for adapting to climate change. Koblenz: International Commission for the Protection of the Rhine; ICPR (2013). Development of Rhine water temperatures based on validated temperature measurements between 1978 and 2011. Koblenz: International Commission for the Protection of the Rhine. No. 209.
 Högselius, P. (2022). DN Debatt. ‘Ny kärnkraft måste ta hänsyn till ett all varmare klimat’. Dagens Nyheter, 8 October 2022; Andersson, C., et al. (2022). DN Debatt Repliker. ‘Kärnkraften tar redan hänsyn till ett varmare klimat’. Dagens Nyheter, 22 August 2022. Disclosure: Per Högselius is the author’s PhD supervisor
 Berger, A., et al. (2017). How much can nuclear energy do about global warming? International Journal Global Energy Issues, 40(1/2), pp. 43–78.; Verma, A. & Djokić, D. (2021). Reimagining Nuclear Engineering. Issues in Science and Technology, 37(3), pp. 64–69.
 ICPR (2015); Rogelj, J., et al. (2018). Mitigation Pathways Compatible with 1.5°C in the Context of Sustainable Development. In: Calvin, K., et al. (eds.) Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty. p. 82; Berger et al. (2017).
 Busby, J. W. (2013). Vaunted Hopes. Climate Change and the Unlikely Nuclear Renaissance. In: Stulberg, A. N. & Fuhrmann, M. (eds.) The Nuclear Renaissance and International Security. Stanford: Stanford Security Studies, pp. 124–153.; IAEA (2020). Climate Change and Nuclear Power. Vienna: International Atomic Energy Agency. No. STI/PUB/1911; Rose, T. & Sweeting, T. (2016). How safe is nuclear power? A statistical study suggests less than expected. Bulletin of the Atomic Scientists, 72(2), pp. 112–115.
 Prognos (2014). Comparing the Cost of Low-Carbon Technologies: What is the Cheapest Option? An analysis of new wind, solar, nuclear and CCS based on current support schemes in the UK and Germany. Berlin: Agora Energiewende. No. 037/03-A-2014/EN; Portugal-Pereira, J., et al. (2018). Better late than never, but never late is better: Risk assessment of nuclear power construction projects. Energy Policy, 120, pp. 158–166; Sovacool, B. K., et al. (2020). Differences in carbon emissions reduction between countries pursuing renewable electricity versus nuclear power. Nature Energy, 5(11), pp. 928–935.
 European Commission (2011). Investment needs for future adaptation measures in EU nuclear power plants and other electricity generation technologies due to effects of climate change. Brussels: European Commission – Directorate-General for Energy. No. EUR 24769; Kopytko, N. & Perkins, J. (2011). Climate change, nuclear power, and the adaptation-mitigation dilemma. Energy Policy, 39, pp. 318–333; Ahmad, A. (2021). Increase in frequency of nuclear power outages due to changing climate. Nature Energy, 6 pp. 755–762.
 Clarke, B. J., Otto, F. E. L. & Jones, R. G. (2021). Inventories of extreme weather events and impacts: Implications for loss and damage from and adaptation to climate extremes. Climate Risk Management, 23, p. 100285; van Oldenborgh, G. J., et al. (2019). Human contribution to the record-breaking June 2019 heat wave in France. World Weather Attribution; Barber, G. (2022). Nuclear Power Plants are struggling to stay cool. Wired, 21 July 2022; Vautard, R., et al. (2019). Human contribution to the record-breaking July 2019 heat wave in Western Europe. World Weather Attribution; Ciavarella, A., et al. (2020). Siberian heatwave of 2020 almost impossible without climate change. World Weather Attribution; Philip, S. Y., et al. (2021). Rapid attribution analysis of the extraordinary heatwave on the Pacific Coast of the US and Canada June 2021. World Weather Attribution.
 Kaijser, A. & Meyer, J.-H. (2018). Nuclear Installations at the Border. Transnational connections and international implications. An Introduction. Journal for the History of Environment and Society, 3, pp. 1–32.
*Cover Image: Low water levels at sunset, Upper Rhine in Karlsruhe Maxau (2018, next to the Rhine bridge between Baden-Württemberg and Rhineland-Palatinate). Photo by author.
[*Cover image description: Low water in a river exposing strips of land. In the background, there is a horizon with trees and some low infrastructure and buildings. The sun is setting. The sky is a dusky orange and purple, and the purple reflects in the water. Figures of two people are silhouetted on one of the exposed flats of land above the water line.]
Edited by Anna Guasco, reviewed by Asmae Ourkiya.