It is the received wisdom that nuclear weapons and nuclear power are inseparable. Consequently, any country that builds a civilian nuclear power station is able to build an atomic bomb within a couple of years.
Information about the physics of a nuclear weapon’s core is probably not the limiting factor in nuclear proliferation. The critical part of a nuclear bomb, which sets it apart from any other weapon, is the presence of an amount of a material (known as fissile material) that is capable of maintaining a nuclear chain reaction (called the critical mass). This usually means either uranium or plutonium.
While uranium is naturally occurring, plutonium is for all practical purposes a synthetic element – only produced by man.
However, it’s not as simple as digging up sufficient uranium ore and extracting the uranium metal. Only one isotope of uranium (235U) and one of plutonium (239Pu) can conveniently be used to manufacture a weapon (I’ll explain what the numbers mean below).
235U only occurs as around 1% of natural uranium. The other 99% is238U.