This is a little more complicated than what you can learn from wikipedia. Many thousands of US and Soviet nuclear weapons were demilitarized under the START tr

This is a little more complicated than what you can learn from wikipedia. Many thousands of US and Soviet nuclear weapons were demilitarized under the START treaties, mostly at the PANTEX plant in Texas. Demilitarized means that they were disassembled and/or damaged in such a way that they cannot be used for military purposes without extensive reprocessing or re-manufacturing. The demilled components are still radioactive, toxic, and/or classified, so they have to be securely stored somewhere. The parts from old weapons that have completely or partially been dismantled are also held in storage. Some of the non-fissionable materials can be recycled, but the uranium would require reprocessing and re-manufacturing to be used in a weapon. It may be possible to reassemble old weapons from these components, but for what purpose? These weapons were retired for practical reasons such as being replaced by newer, better, and safer weapons (from the point of view of the DOE and DOD). There are also complete weapons in storage that are no longer in active service. Inactive weapons are unmaintained, but could be returned to service with field level maintenance. Some of these are kept to support war plans for contingencies or capabilities that are not a current priority. For the majority though, there's a significant cost to dismantle them and no pressing need to do so.