If you eliminate gas and coal powered plants then the costs of nuclear plant lifecycle is incidental compared to economic losses that a country would encounter if they relied on solar and wind.
The dirty secret about "clean energy" is that it isn't actually very clean. When you eliminate big coal plants and try to use solar or wind, what you are actually doing is moving your dependence from coal to natural gas.
Those wind farms and solar farms require significant investment in numerous smaller style natural gas plants in order to function correctly.
So, right now, when people think they are moving away from fossil fuels they are really just moving to natural gas that is supplanted by solar and wind when conditions are ideal for them to work properly.
If you want to eliminate your dependence on natural gas, then, the only feasible option is nuclear.