How long the atom bomb can be stored?

Answer 1

Under the correct conditions, indefinitely.

While the mechanics of an atomic bomb can be stored a long time, assuming proper maintenance, the fuel decays noticeably over time. After about a decade of storage, the fuel has naturally fissioned enough to produce "pollutant" fission by-products which ruin the bomb's explosive potential. That is, the fuel naturally decays, and the natural decay atoms will inhibit the proper chain-reaction needed to have a usable weapon. So, the fuel will last about a decade before it needs to be removed and reprocessed.

Also, if the fuel core is stored in the weapon (i.e. the weapon is stored "fully functional"), the residual radiation and heat that the fuel decay gives off causes significant problems for the weapon: the fuel configuration itself may change slightly or crack, the sensitive electronics may suffer damage from the gamma radiation emitted, and the chemical explosives may likewise suffer degradation.

Overall, while the time a given weapon design can be stored varies, and the exact times are of course classified, it seems that discussions about such topics in the open literature indicate that an atomic bomb needs to be serviced and checked regularly (at least every 6 months or so), and that few can be stored for more than a decade before needing a serious overhaul.