28 September 2021

Short and long-term impact of weather on French nuclear production

Weather conditions can have a significant impact on the production of French nuclear power plants: over the last six years (2015-2020), heat waves and droughts caused nearly 360 outages or deratings, resulting in up to 6.2GW of unavailability.

Since its creation in 2019, Callendar has acquired an unique expertise in short-term forecasting of these outages and in modeling the long-term effects of climate change on nuclear production. We have conducted several innovative projects in this field, including

  • Systematic identification of past weather-related unavailability of French nuclear reactors,
  • The creation of temperature and flow databases at French nuclear power plants,
  • The creation of models for the prediction of future unavailabilities.

This work has concrete applications, in particular for the short-term prediction of outages caused by temperature or lack of water. It has also been featured in various publications, for example by the French TSO RTE or in the World Nuclear Industry Status Report 2021.

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How exactly can weather lead to the unavailability of a nuclear reactor?

Nuclear power plants, like most conventional power plants, need water to cool their turbines and produce electricity. In France, each plant has its own rules governing the use of water. These regulations can, for example, limit the temperature at the discharge point or downstream. The details of these regulations are available in French here.

In periods of heat or drought, these limits may become impossible to meet. In this case, the operator must reduce production or shut down reactors.

Does the weather have a material impact on electricity market?

Between 2015 and 2020, we identified 357 total or partial unavailabilities caused by weather. The most severe episode took place on July 25, 2019: it affected 9 nuclear reactors simultaneously, representing an unavailable electrical power of 6.2GW. This episode led to a significant increase in the price of electricity: over €70/MWh on the spot market in France.

French nuclear power plants' production losses due to weather

Electrical production lost to weather conditions by nuclear plant (2015-2020)

How can we predict the impact of weather and climate on French nuclear reactors?

Weather conditions can affect the operation of French nuclear power plants in two ways: via the temperature of the water used for cooling or, in the case of river plants, via the flow rate:

  • A high temperature of the cooling water can lead to the maximum authorized discharge temperature being exceeded,
  • A low flow rate can lead to the maximum allowed temperature being exceeded after dilution. In periods of drought, water withdrawals or consumption can also be directly limited.

As a result, once the regulatory and technical constraints are known, outages can be predicted by forecasting the flow rate and temperature of the water at each plant. We use machine learning algorithms trained on both public data and measurements performed by EDF to predict hydroclimatic conditions based on weather forecasts, historical norms or climate projections depending on the desired time horizon. This innovative approach is described in more detail here.