Nuclear power
Fission
All of today's nuclear power plants run on nuclear fission.
Supply
Today's nuclear plants depend on uranium-235, which is far too scarce. If the whole world was powered this way, we'd start to run out of it in less than 4 years:
Citation:
Uranium 2020: Resources, Production and Demand ('Red Book')
"The total recoverable identified resources to $260/kg U is 8.070 million tonnes U."
Citation: Key World Energy Statistics 2020 (IEA report) - Page 73 - Glossary - Nuclear
Does not include the fuel used in generating electricity. See [energy.tes] for that.
Citation: "Key World Energy Statistics 2020" IEA
- Page 47 - Simplified energy balance table - World energy balance, 2018
We'd run out even faster (calculation loading)if all nations were developed.
Since uranium-235 and uranium-238 occur together in nature
These two problems could be solved with breeder reactors that make use of uranium-238 and/or thorium - both of which are far more abundant fuels. However, major innovations are needed before this is viable and safe.
For now, nuclear power is best suited as only a baseload.
There is also some talk about extracting uranium from seawater, but the viability of this is questionable (like other trace minerals), because the concentration is extremely low.
Safety concerns
Proliferation
If uranium gets into the wrong hands, it can be used to make thermonuclear bombs. Nuclear power plants need strong redundant security measures to mitigate this risk.
Meltdowns
This has happened twice in history: Chernobyl and Fukushima.
Fusion
Nuclear fusion is not currently viable for generating power. It has great potential solve the energy crisis
The most recent breakthrough was in December 2022. Fusion research & development is certainly worthwhile, but we can't "put all our eggs in one basket". Climate change is near a tipping point, so we need clean energy sooner than fusion might be available.