Soviet nukes used relatively impure weapons-grade fissionables by Western standards. It decayed fast due to the impurities and had to be removed and "recooked" every 8-10 years. The Soviets found it easier to do that than to cook the stuff right the first time.
I wouldn't worrry about xSoviet nukes. At this point they will likely just fizzle and cause an ungodly mess. The backpack types would likely not even do that.
If it ever happened most likely the KGB guys sold those sand simians a case full of lead bars and wires.