Ukraine using a dirty bomb makes no sense at all. They have the world on their side, started a nuclear exchange would completely negate that, and make them just a big a pariah as Russia. They'd be better off joining Russia, and we know that's never going to happen.

Russia nuking, or staging a nuke, on their own troops as an excuse to nuke Ukraine makes a lot more sense. Still not sure what the endgame would be. If the endgame is to have NATO join the war and get his ass kicked even harder then that's the quickest way for Putin to do it aside from attacking a NATO country directly.

I don't think Putin has to either escalate or de-escalate, or if it's the former that it necessarily means using nukes. As it is, I think the war is just going to drag out for a few more weeks if not months before anything like that happens.