A detonation device strapped to barrels of nuclear waste is all you need for a dirty bomb. It can be put together literally in minutes.

I will not argue with your points about what Russia wants to do. You don't know Russia's plans any better than I do. The exact same - the EXACT SAME arguments could be made, and stronger, for Ukraine to set off a dirty bomb.

What Ukraine wants more than anything else is for the US / NATO to enter the war directly. Setting off a dirty bomb and blambing the Russians might accomplish this.

The US has said if Russia sets off a dirty bomb, they will respond, again exactly undermining your argument.