the major problems with nuclear reactors are the disposal of hot water and the disposal of radioactive waste.
The fission reaction produces a great deal of energy. The high temperatures are used to heat boilers that in turn are used to turn turbines to create electrical energy. High energy not a problem.
The fission of Uranium 238 produces Plutonium 238 which can be used both in bombs and in fission reactors in turn. Presently there is no shortage of nuclear fuel in the US or the world ( The US just "sold" 25% of its Uranium mines to Russia)
The high heat is a problem to get rid of the immense heat produced by the nuclear reactions large amounts of cold water are needed to cool the reactors. The cold water absorbs the heat from the reactors and is returned to the environment as warm water. This change in the temperature of the water creates changes in the local envirornments often harmful.
The biggest problem is what to do with the nuclear waste. When the concentration of fissionable isotopes drops to low to be useful in the production of electricity it needs to be replaced. The used fuel rods need to be stored for 1000s of years before the level of radioactivity drops to a "safe" level. There is presently no solution as to how to safely store the waste for the vast periods of time required.