Professor John Robertson OBA

TuS Reader Legerwood commented yesterday under our piece on the widespread corrosion of Frances’s nuclear reactors (https://talkingupscotlandtwo.com/2025/06/27/reliability-of-nuclear-energy-takes-another-blow-as-france-fears-return-to-2022-when-57-of-all-reactors-were-offline-due-to-corrosion/):

It is not just corrosion in its nuclear reactors that France has to worry about.

The high temperatures that France now regularly experiences -at the moment 40C or above – affects the nuclear reactors and can lead to them being taken off-line. The high temperatures also heat up river water etc and reduce the water available making it difficult to cool the reactors leading to shut downs.

All in all not a good time to go nuclear when the climate is changing.

Just so, as the above ‘heat dome‘ is predicted for France and even parts of the UK in the next few days.

Is there any research supporting the above thoughts?

Indeed, this:

As ambient temperature rises, the production of electricity at nuclear power plants may decrease as a result of both efficiency losses in direct cooling systems and their inability to operate at full capacity. [2]

First, an increase in external temperature lowers the efficiency of power plants in generating electricity. As aforementioned, an advantage of using a direct cooling system is that it utilizes the naturally cool water of lakes and rivers. For example, as observed in Fig. 1 Isar Nuclear Power Plant utilizes its proximity to the Isar river as a natural coolant (see Figure 1). However, as ambient temperatures rise, so does the water sources. Simply put, when the coolant liquid is warmer, it is less effective at condensing the steam that is used internally because it cannot absorb as much of the thermal energy. Thus, the system operates less efficiently. Previous quantitative research suggests that for every 1˚C increase in outdoor temperature, electrical output decreases by between 0.37 – 0.72%.

Secondly, an increase in temperatures decreases the amount of electricity nuclear power plants are able to produce due to an inability to operate at full capacity. First, a nuclear power plants operation is greatly limited by the condensers maximum pressure. The condensers maximum pressure is determined by the design of the plant and mechanical limitations of the condenser itself. As the ambient temperature increases, the condensers pressure increases proportionally. As the outdoor temperature increases, the condenser will eventually reach its maximum pressure, depending on design, and the plant will be obligated to reduce fuel use, and thus, output. Second, most countries have enacted regulations to limit thermal pollution in lakes and rivers to mitigate impacts on local ecosystems. As follows, if the temperature of the body of water used as coolant increases, then the water will be able to absorb less heat before surpassing the allowable temperature limit for return to water. In these cases, the plant must reduce production to keep the temperature below the limit.

It must be noted that all thermal power plants have exposure to these two impacts, however, because water requirement per electric output is higher in nuclear power plants compared to other thermal power sources, nuclear plants are more vulnerable.

http://large.stanford.edu/courses/2018/ph241/duboc1/

What is predicted for UK?

Five regions of the UK have been placed on an amber heat health alert until Tuesday, with temperatures set to reach 36C on Monday in parts of the country. It comes as wildfires and flooding have swept across the continent this week.

Health services in the East Midlands, South East, South West, London, and the East of England have been placed on the second highest heat alert, while a yellow alert is in force in Yorkshire and Humber, and the West Midlands. An amber alert was previously issued for all regions in England on June 19, the first time it had been used since September 2023.

https://www.msn.com/en-sg/news/other/europe-scorches-under-intense-heatwave/ar-AA1HBIZi?ocid=BingNewsSerp