I'm fairly certain current global warming concerns are not caused by heat generation but by heat retention. And we do generate a lot of heat via fossil fuels.
So generating additional heat (adding heat to the system) is not a current or future concern as long as heat retention stops growing
Doesn't matter if the heat is coming from burning more fossils or nuclear fuels or intercepting more solar light - the effect on Earth's temeperature is negligible for now. You can do simple heat balance with Stefan Boltzman Law to show that the temperature of the Earth would increase by less than a tenth of a degree even if we burned 10x more fossil or nuclear fuels. The idea is that all the energy received and and generated on Earth must be reraridated at the Earth's blackbody temperature, and it only changes as the power to the 1/4th - so very small compared to the absolute temperature of the Earth ~300K, and the changes (e.g. seasons).
So generating additional heat (adding heat to the system) is not a current or future concern as long as heat retention stops growing