Lots of it is lost to heat with legacy fossil generation.

You have pretty much the same heat losses with nuclear, or anything else where you heat water to turn a turbine.

Nuclear is low carbon, it’s fine we lose heat to extract that energy versus stationary and mobile combustion generation, as there is no other effective way to extract that energy at this time.

Quantification of global waste heat and its environmental effects - https://www.sciencedirect.com/science/article/abs/pii/S03062... - Applied Energy Volume 235, 1 February 2019, Pages 1314-1334

* 49.3–51.5% of global energy use would end up as waste heat in 2030.

* Transport sector accounts for the largest (43%) recoverable waste heat in 2030.

I made no claims about carbon.