That lazy line again:
During the heatwave between 28 June and 2 July, 17 out of France’s 18 nuclear power plants in the country faced capacity reductions, with some shut down completely.
Nuclear power plants n France have scheduled maintenance in summer (because despite what the article suggests, this is a low in power consumption)
Capacity reduction happen in that context, with extremely stringent regulations in some rivers that prevent any sort of warming of the water above some temperatures.
It does not impact the power plants that rely on water evaporation which, let's remind it, release colder water than they take in (but in a lower volume)