To produce electricity, you need water.
Lots of water.
While France is going through a record drought, one of the country's biggest users finds itself in the sights of environmental associations and at the heart of government concerns.
This is the nuclear fleet.
According to an inventory of aquatic environments by the Ministry of Ecological Transition, half of the 32 billion m³ withdrawn in France in 2017 was for the operation of power plants (mainly nuclear).
However, this figure has fallen by 20% since 2003.
These take and reject, in rivers and at sea, a lot of water to cool their reactors.
“For 26 of the 56 French reactors, those close to the sea which are in open circuit, they each need 50 m³/second.
For the other 30, who are inland and whose water vapor you see coming out of the chimneys, it's 2 m³/s", explains Olivier Dubois, deputy director of expertise at the Institute for Radiation Protection and nuclear safety (IRSN).
Water is therefore an essential resource for the operation of the nuclear fleet, even if it is never in contact with the reactor or the primary circuit.
“If we can't cool down, the reactor is shut down and no longer produces.
You still need a minimum of water to be able to evacuate the heat from the radioactive waste", continues the French expert whose teams have created a working group on the impact of the safety of nuclear power plants in the face of "heat wave aggression". .
The number 1 risk of a heat wave, for the nuclear fleet, is therefore to ensure a certain level of throughput.
By mid-August, more than 99% of rivers had flows below historical averages.
Faced with the colossal decrease in flow and water level in certain rivers in recent weeks, "great lakes", also used for leisure and human consumption, must in fact release water to supply these rivers in order to preserve the fauna and flora as well as to ensure the operation of nuclear power plants.
The Loire, having less flow than the Rhône, is particularly affected by these releases.
“In the future, there may be conflicts of use,” warns Alexis Guilpart, coordinator of the water and aquatic environments network at the environmental NGO France Nature Environnement (FNE).
“We shouldn't have to choose between producing electricity and having drinking water”.
Water that can be discharged up to 36°C
The second risk of such a heat wave does not concern the quantity of water, but its quality.
These billions of m³, the equivalent of three times the drinking water produced in France each year, are in fact then largely discharged (a small part evaporates) into the rivers from which they were taken... but not to the same temperature.
The discharged water is much warmer, a regulated temperature difference and under close surveillance, so as not to disturb the ecosystem.
“For example, in normal times, the Blayais nuclear power plant (Gironde) can only discharge water at 11°C more than that which flows into the Gironde estuary, reports Alexis Guilpart of FNE .
This summer, these sites were allowed, thanks to a decree, to return the water they used up to 36.5°C”.
Why ?
Because throwing hot water into a river at full flow does not cause the same temperature rise at all as in a river with very low flow.
Compliance stricto sensu with environmental standards would thus have led to the closure of many reactors this summer.
At the request of EDF, a decree, published in the official journal at the beginning of August, allowed five power stations to discharge warmer water into the environment in order to allow them not to stop or slow down their reactors.
This derogation currently extends until September 11.
"With these dry and hot summers, we have increasing difficulties in maintaining production in compliance with environmental constraints", agrees the nuclear expert at IRSN.
The NGO recalls for its part that "these hot water discharges are considered as thermal pollution which will affect fauna and flora".
"With this decision, we admit that we will make aquatic biodiversity the adjustment variable for our energy needs", still attacks Alexis Guilpart.
According to him, the areas impacted by these hot discharges “will expand because the water takes more kilometers to cool.
He also regrets that these discharge water temperature thresholds are established only on the basis of the sole criterion of fish viability.
“This criterion is insufficient.
Because of the warming of the rivers, parasites develop or the food resources of the fish can be disturbed”.
Read alsoHydroelectricity: dams also suffer from drought, their production is “historically low”
The State must in any case juggle between the constraints to maintain the production of electricity for some months, because the series of bad news does not stop there.
To this must be added the 40% drop in the production of hydroelectric dams, which have dried up due to the lack of rain.
An equation made even more complex in this period of uncertainty on the energy market due to the war in Ukraine.