They are getting real close to developing plutonium(if the North Koreans have already given them the technology)
Manufacturing weapons grade Plutonium is not all that difficult compared to separating Uranium isotopes. It's the difference between the chemical separation of two different elements versus separation of isotopes of the same element with a vary slight difference in atomic weight. One is industrial chemistry and the other is a process of moving material atom by atom into different bins as it were.
Plutonium is the usual fuel of implosion devices which are fairly simple in concept but extremely difficult and demanding in actual construction. In comparison gun type bombs are much easier to construct once you have the Uranium to fuel them. It is possible to construct a gun type device with no electrical/electronic parts of any sort which is an advantage over the implosion devices as most of the switching/timing/detonators/neutron sources are dual use tech and are very tightly controlled.
Regards,
GtG