Nuclear power has a larger carbon footprint than you might think: from the concrete used to build the stations, to the energy used in the mining, extraction and refining processes to produce the fuel. It can take more than 6 years to mitigate the energy used in building of the facility, let alone the actual construction costs.
On account of the fact that every utility scale fission reactor design is really nuclear steam power, every watt of power it produces requires two watts of heat dissipation using water. Of course this means the plants have to shut down if it's too hot, and that source of fresh water you were drawing on is not as cool as it was when the plant was built (eg, due to climate change).
It's also super expensive, because risks must be mitigated; some have pointed out this has led to a negative learning curve of nuclear power.
Much as it is kind of cool that people are using nuclear physics to make power, it really is very dated technology. Phasing it out in favor of cheaper, safer alternatives is a much better idea: with the advent of flow batteries, liquid metal batteries, you don't need to have peaking power plants paired with the renewables. You just need more renewables.