They key difference between nuclear and fossil fuels is the emissions each generates. Fossil fuels burn into greenhouse gasses which trap in heat. If we switch to nuclear, those greenhouse gasses won't accumulate as much.
While thermal pollution in Earths atmosphere is a very real and relevant issue with energy generation and all kinds of other human activities; A whole bunch of French fission nuclear reactors are regularly shut/throttled down during summer heat waves due to lack of appropriate cooling.
The combination of these factors sometimes makes me wonder if the game Oxygen Not Included is a crude simulation of what we are doing to this planet. There the biggest end-game problem is the asteroid colony overheating due to creating a whole bunch of extra heat inside of it from using up fossil fuels, yet lacking any good way to actually vent all these massive amounts of extra heat from the little biosphere.
Back on earth, thermal radiation is sending massive amounts of heat into space. Additional heat we put into the atmosphere will not stay for long enough to matter, compared to certain gases that block thermal radiation.
I'm just not too sure about that; Fossil fuels took millions of years, and massive natural forces, to accumulate in their modern day form, very similar to uranium and other energy resources. That's a lot of energy that went into "making" them over a lot of time.
But humanity is "unloading" all that energy, with all its effects including thermal radiation, into the atmosphere at extremely faster rates than it took to accumulate. And we've been doing it at a literally global and industrialized scales.
We even recognize the problem of thermal pollution on a "micro" level when we throttle and shut down generators, reactors and industrial processes that threaten to overheat the natural water bodies they use for cooling.
I see no reason why these issues can't accumulate and scale up to global levels.
Disregarding that possibility, as if humans couldn't screw up the planet on such scales, are exactly what made us run head first into global warming trough CO2 emissions and littering most of the planet with led and plastics.