What's the Difference Between a Low Yield Nuclear Weapon and a Nuclear Power Plant?

The two nuclear power plants that have been shelled are both east of Kyiv. The prevailing winds are out of the West, which means if either one of them went down, it would carry the radioactive plume over Russia. We should get Kevin Campon from Beyond Nuclear and just ask him what's the difference between a low yield nuclear weapon and a nuclear power plant going down? I suspect there's a huge difference, but I may be wrong.