TRUE OR FAKE. Do nuclear power plants contribute to the warming of the Mediterranean, as assured by Jean-Luc Mélenchon?

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Nuclear power on Jean-Luc Mélenchon’s grill. During the closing meeting of the summer university of France insoumise, Sunday August 28, the leader of the Insoumis embarked on a full attack against the atom. “Nuclear is not a safe energy“, he judged in front of nearly 5,000 activists. To the tribune, the rebellious leader targets the discharge of cooling water from nuclear reactors into the environment: “it is being criminal to give authorizations so that we reject in water, the part of water which will be consumed to cool the plant”, he is indignant. Jean-Luc Melenchon is convinced, “nuclear power plants […] are contributing to the warming of the Mediterranean Sea which they have almost already transformed into a cesspool.” The leader of the Rogue is he right to make nuclear power responsible for the rise in the temperature of the waters of the Mediterranean?

By their operation, nuclear power plants do release heat, “thermal energy“resulting from”uranium fission“, confirms with franceinfo Sylvain David, CNRS research director and nuclear specialist. This energy is mainly used to generate water vapor intended to make turn enormous turbines linked to an alternator, as for a dynamo in which the movements are transformed into electricity. Some of this heat is nevertheless “discharged into the environment“, explains the researcher: to cool the steam used by the turbines, the power plants pump water directly from the rivers, then return it to nature with a temperature higher by a few degrees compared to that where it was extracted.

This is not without effect on the river environment. A report published in 2016 by EDF on the thermal study of the Rhône, on the edge of which four power plants are installed, indicates that the rise in temperature downstream of a nuclear site can reach 6 degrees. On average, this increase is between 0.5 and 1.6 degrees.

The temperature of the “thermal discharges” is however “regulated“recalls Sabrina Speich, Professor of Geosciences and member of the Dynamic Meteorology Laboratory (LMD) of the Ecole Normale Supérieure.You can’t spill [une température de] 90 degrees and there is environmental water monitoring“, notes the researcher. And the air-cooling towers present in some power plants allow cooling by “the atmosphere“, specifies Sylvain David, which limits hot water discharges

The heat wave of 2022, however, prompted the Nuclear Safety Authority (ASN) to raise the regulatory ceiling for discharges from certain power plants. According to France Bleu, the nuclear site of Tricastin (Drôme) has thus received an exemption to carry out spills beyond the limit of 28 degrees for a new threshold set at 30 degrees.

Gold “beyond 25 degrees, there is a whole procession of fish which simply does not survive”, is alarmed by franceinfo, Alexis Guilpart, coordinator of the water network at France Nature Environnement. “A higher stream temperature will [engendrer] development of parasitism on [les] Pisces. This will also promote the proliferation of certain micro-algae that we do not want to see develop,“adds the specialist.

The discharge of cooling water from nuclear power plants can therefore actually contribute to the warming of rivers. But is it possible to say the same for the Mediterranean? Contacted by franceinfo, the Institute for Radiation Protection and Nuclear Safety (Irsn) wishes to point out that there are no French nuclear power plants in the Mediterranean. As for the influence of reactors located upstream from the sea, mainly on the Rhône, in Tricastin, Cruas-Meysse, Saint Alban or Bugey, the scientists questioned by franceinfo are unanimous: French nuclear power plants have “no overall impact [sur le réchauffement] of the Mediterranean“says Sylvain David with certainty.

“There is no measurable difference” about the presence or absence of nuclear power plants on the rise in the temperature of the Mediterranean Sea, abounds for his part Wolfgang Cramer, research director at the CNRS and contributor to the IPCC. If the reactors “discharge a lot of hot water into the rivers“, when these discharges reach the sea, “the impact is insignificant“, confirms the researcher. Compared “to the volume of the Mediterranean“(3,700,000 km3 according to the Marine Observatory), points out Sabrina Speich, the flow of the Rhône (about 1,680 m3 per second according to EauFrance) is “very weak“, while the water withdrawal from a power plant according to a report published by EDF in 2020 on the Tricastin site, only amounts to 50 m3 per second. In the Channel, in Flamanville or Gravelines in particular, On the other hand, nuclear sites discharge their cooling water directly into the sea. But it appears that this practice also has no significant consequences on the environment. According to a study by Milieu Marin France published in 2012, these “heat discharges are very quickly dispersed by the currents“and none”noticeable imbalance in the environment [marin]“wasn’t”highlighted“.

The rise in the temperature of the Mediterranean is above all caused by “the climate change“, slices Sabrina Speich. “90% of excess energy caused by greenhouse gases” is found in the seas and oceans reveals the climatologist quoting an article from the scientific journal Earth System Science Data, published in 2020. “CThis is also true for the Mediterranean“, adds the professor. An observation also shared with franceinfo by the Irsn: “the contribution of the operation of nuclear power plants to the warming of the Mediterranean is totally negligible compared to that linked to the rise in temperatures due to global warming“, confirms with franceinfo the nuclear security agency.

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Participate in the consultation initiated as part of the European project De facto on the Make.org platform. Franceinfo is the partner


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