The land of the flighty

[Lissa]

I had read that it was deep underground, and that it was either really tiny, or a dud. Most likely a dud, since trying to get a small nuclear pile fissile is harder (read critical mass). So they did probably conduct a nuclear test, but it turns out that NK has the worst nuclear scientists in the history of weapons testing. A handy set back for anyone interested in nuclear non-proliferation, since now the world can intervene to help prevent subsequent progress toward folly.

No, it's very easy to get a critical mass (if it took only a critical mass, reactors everywhere would be detonating on their own accord). The problem is critical density. You will get a fizzle (a weak detonation) if you don't reach the critical density or your shaped charges do not compress the pit properly.

And truth to be told, the US government is more worried about the items that are required to precisely fire the shaped charges than the actual weapons grade material. If you have the ability to get those devices, you can make far more power weapons, be they conventional or WMD.