A nuclear winter would last at most a decade or two due to the dust thrown into the atmosphere by the explosions. A disaster like Chernobyl, while not even close in terms of destructive power, had the potential to release enough radiation to leave half of Europe uninhabitable for centuries, maybe even millenia. Chernobyl is still dangerous to this day while cities like Hiroshima and Nagasaki are thriving.

And to think you could just abandon a nuclear power plant safely...

You realize used nuclear fuel is extremely hot and still radiating heat and has to be cooled for a long time. You abandoned one without safety measures and the pools cooling the used fuel would just boil and evaporate. The water gone would no longer shield the radiation and you'd have a ton of radioactive material shitting poison into the atmosphere and meltdown.

Some people don't know shit about nuclear power and like to act condescending "it's not like a nuclear bomb". No, it's far more dangerous. And all it takes is a couple of really bad accidents to ruin the planet. And Murphy's law tells us those improbable accidents will happen eventually. That means with nuclear power, quick or slowly we are walking towards the abyss. When we reach it we fall and there's no way out.