20 to 40 years, depending on the exact design. Most were never kept in stockpile that long. However as we can't test new designs several stockpile weapons are now beyond their design lifetime.
The early ones had some components with a shelf life under 6 months, but frequent replacement of those components could keep them usable for many years.
USSR
Nobody, the US was the first country to work out how to actually make nuclear weapons.
The US has 104 operating reactors and none of them have exploded. It's a matter of good design and operating methods. Nuclear explosions though are not possible in a commercial nuclear reactor, because the nuclear fuel is not sufficiently enriched to make a weapon, whatever happens in the reactor.
The US performed the first nuclear weapon test on July 16, 1945.
End of WW2.
never, most of their nuclear weapon activity was for propaganda purposes.
US
They were pretty nervous...................
no one can have a nucular weapon except the government and such
no
The Manhattan Project.
Manhattan project