Although the theory the japanese program was working on probably wouldn't lead to a really serious atom bomb, it could lead to the development of a serious trigger which could also serve as a "tactical nuke".
My prediction ~ a less than 1 kiloton explosion ~ just like the earlier ones. Again, it can be used as a trigger and they may have improved its performance.
Try reading this piece on recent discoveries with electrons ~ then think about what a 'fizzle bomb' accessing this process might do; http://phys.org/news/2012-04-electrons.html
You seriously believe the Japanese gave nukes to the Norks?
NK is a client state of China more than anything