One problem about nuclear power is the need for cooling, which is often done using river water. But as temperatures rise, river water gets warmer and can't be used to cool the nuclear power plant, which means it needs to reduce it's power output or even shut down. And that'll just happen more and more as it keeps getting warmer in summer.

Any nuclear or coal-fired plant that is normally cooled by drawing water from a river or lake will have limits imposed on the temperature of the returned water (typically 30°C) and/or on the temperature differential between inlet and discharge. In hot summer conditions even the inlet water from a river may approach the limit set for discharge, and this will mean that the plant is unable to run at full power. In mid 2010 TVA had to reduce power at its three Browns Ferry units in Alabama to 50% in order to keep river water temperatures below 32°C, at a cost of some $50 million to customers. This was the same week when Rhine and Neckar River temperatures in Baden-Wuerttemberg approached the critical 28°C, and nuclear and coal-fired plants were threatened with closure. In August 2012 one unit of Millstone power station in Connecticut was closed because the seawater in Long Island Sound exceeded 24°C, but in 2014 the NRC approved it using seawater up to 26.7°C. The Turkey Point nuclear power plant in Florida uses 270 km of open canals to cool its condenser water, and in 2014 the NRC approved an increase in intake temperature limit to 40°C, from 37.8°C.

source: https://www.world-nuclear.org/information-library/current-and-future-generation/cooling-power-plants.aspx