In order to attain a nuclear chain reaction, the explosives timing needs to be precisely controlled so that all 360 degrees of the core is compressed by the explosion uniformly to within thousands of microseconds. That kind of accuracy requires maintenance or replacement of resistor networks, capacitors, software, firmware, clock oscillators, and the conventional explosives that compress the fissile material. What makes you think they'd use an implosion device, when a simple gun device obviates all need for precision timing, triggers, shaped charges, electronics, blah blah blah?
Of course, the devil -- in this case -- in in only one detail: They'd need to get their grubbies on some HEU, which is why the US and Russia have been scrambling to get all of it under lock and key from a variety of research/edu/etc. facilities in Eastern Europe as of late.
Of course so much of the stuff has been manufactured over the years, much of which (courtesy of the $&#&*# USSR) has not been accounted for (and then there's North Korea, and other rogue nations capable of spinning some centrifugen), so no matter how much we and the Russians manage to get under lock and key, it still doesn't prove the negative, so to speak. In other words, we can go snarfing up HEU 'till the cows come home, but the only thing we'll know for certain is that the actual HEU the US/Ruskie teams captured is off the market. There's no way to know about any other HEU that might be out there.
Anyway, my point is that we should not take comfort in the difficulty involved in setting off a successful plutonium implosion device, because if the bastards get their hands on some weapons grade uranium, the only "technology" they'll need is a saw, to cut down the barrel of an old field artillery piece.
"What makes you think they'd use an implosion device, when a simple gun device obviates all need for precision timing, triggers, shaped charges, electronics, blah blah blah?"
That's simply untrue. Fire your core projectile either too fast or too slow and you will get a fizzle, not a boom. Allow any of your exhaust gasses to race ahead of your fired projectile and they will fracture your core target into a worthless shape. Ditto for vibrations from your shot (they frequently travel faster through metal than does the projectile itself, similar to how earthquake shock waves travel faster through rock than does the sound they they emit through the air above). And the speed of your shot is going to constantly be changing as the radiation deteriorates your convention explosives and electronics. You also have to deal with how fast your atomic trigger decays, and same again for how the natural radiation decay in your core and shell/case forms non-uniform impurities in what was once supposed to be a pristine shape of fissionable material.
You don't make nukes with a hacksaw and an old iron pipe. That sort of fantastic oversimplification is little more than an old wives' tale.
Consider that the entire might of NAZI Germany couldn't get one of these instantaneous self-sustaining chain reactions in 8 years of trying. In more than half a century, fewer than a dozen *nations* have managed to get past the technical hurdles for these beasts.
There are simply very few people who understand how to transport the shaped core and shell/case without causing micro-fractures in their hyper-brittle structures, without exposing the heavy metals to enough air to cause near-instant rust, and fewer still who can precisely shape the heavy metals involved.
See Post #95.