If a nuclear reactor is run normally for a prolonged period of time, the plutonium produced will be 19% or more Pu-240, with 80% or less Pu-239. Weapons-grade plutonium must have less than 7% Pu-240. Pu-240 cannot undergo nuclear fission, while Pu-239 can. However, if a nuclear reactor is run just long enough to produce Pu-239 out of the uranium but not long enough to create Pu-240, the resulting spent nuclear fuel will have enough Pu-239 to be weapons-grade. Running a nuclear reactor for a short amount of time can easily create weapons-grade plutonium, where up to 93% of the plutonium created is Pu-239, leaving between 6 and 7% Pu-240.  The ability to create Pu-239 from uranium used for nuclear power means there is a connection between nuclear power and nuclear weapons. It is feasible for countries that have the necessary equipment for nuclear power to also produce, if nothing else, weapons-grade plutonium.