During World War II the United States spent a large amount of money on developing nuclear technology. Much of that investment went into industrial systems designed to separate U-235 from U-238, or to transform U-238 into Pu-239. Here such systems were built in Oak Ridge, Tennessee, My childhood hometown. The Uranium separation technologies were gaseous diffusion, thermal diffusion and electromagnetic separation. In addition, Plutonium was produced in the Graphite Reactor. Of the 4 technologies, thermal diffusion was the least successful.
Gaseous diffusion was a successful but expensive to develop and operate technology Gaseous diffusion production was developed by the United States, the Soviet Union, China, the United Kingdom and France. The major drawback to gaseous diffusion is the expense of operation. The technology requires a lot of electricity. For this reason gaseous diffusion plants are being shut down and replaced by centrifuges.
The Oak Ridge X-10 Graphite reactor was never intended to produce plutonium for weapons, instead the reactor was intended to support research, that would contribute to the development of the Handford weapons complex.However, given enough time the X-10 Graphite reactor could have produced enough weapons grade Pu-239 to build one or more nuclear weapons. In fact the United Kingdom’s first two military grade Pu-239 facilitated designs that were closely related to that of the graphite reactors. The design of later Pu-239 production reactors used graphite cores. Finally the design of the reactor which North Korea uses to produce its nuclear devices is closely related to the UK’s Second Generation weapons productions Reactors. The Handford Reactors were water cool graphite piles, a design that was also adopted by the Soviet Union.
I should mention two more Uranium separation technologies. The first is is the centrifuge. Ye centrifuge uses far less electricity than the Gaseous diffusion method, but is relatively simple to build. Even Nations that are nor highly advanced industrially, are capable of producing Centrifuges, and centrifuge arrays, capable of producing weapons.grade U-235. Pakistan’s nuclear weapons program is based on centrifuge technology, even though Pakistan is not advanced industrial state.
I should mention one more successful Uranium separation, the Aerodynamic separation process. This system is in expensive to build, and has been successfully used by South Africa to produce the U235 needed to manufacture 6 nuclear weapons. The major drawback of Aerodynamic separation is that it requires a lot of electricity. Yet if a small country wishes to produce a few nuclear weapons at a relatively low cost, Aerodynamic separation is the way to go. On the other hand, Aerodynamics separation is not as low cost as centrifuge separation for a bigger5 nuclear program.
Thus any nation would have a wide variety of tested options available to it, If it wished to produce locally made weapons grade materials. The cost of producing a limited amount of such material is not great, and there are tested production methods.