A simple program could be based around reprocessing plutonium from a relatively small reactor, but a more advanced program needs uranium and tritium (used in thermonuclear weapons). Uranium requires extensive energy resources to operate the enrichment facilities (traditionally near gigawatts of hydropower, coal, or nuclear capacity), and tritium is best produced in heavy water reactors. Heavy water reactors need heavy water (an isotope extracted from regular water), which tends to be produced at large hydroelectric facilities due to the energy and water requirements.
The largest bottleneck is acquiring weapons grade material, either plutonium or highly enriched uranium. HEU is probably more difficult to acquire due to the need for enrichment facilities of some kind, traditionally gaseous diffusion although more recently centrifuges. Plutonium can be acquired by reprocessing spent nuclear fuel.
The easiest plutonium pathway is using a gas cooled reactor, which can use natural uranium and common gases such as carbon dioxide, although it isn't as good at making tritium. Heavy water is the ideal, since it is the best for tritium, but while it can use natural uranium it requires heavy water. Light water doesn't really excel at weapons production, since it needs low enriched fuel and doesn't excel at tritium production, but it's a good option for naval propulsion and commercial programs and thus the most common type of reactor in general use. Gas cooling was a common option when nuclear energy started (the first commercial power reactors were gas cooled units in the United Kingdom) and it could make a comeback in the future due to its high efficiency and high output temperatures (waste heat has potential industrial and heating uses), but it's currently not commercially available and the most advanced commercial plants (British Advanced Gas Cooled Reactors) are 1960s/1970s technology.
The answer is thus that it depends. A simple program just needs a small reactor and reprocessing capabilities, but a large and/or advanced one would really benefit from access to large hydroelectric facilities to help run enrichment plants (nuclear can take over later) and provide heavy water.