[MRadtke]

“And they aren’t old cold war Russian nukes. The highly enriched plutonium or uranium in the trigger breaks down over time. Any weapon build before 1990 is a paperweight now unless new triggers have been put in place. And the trigger is the hardest part of the bomb to build. Again you might be able to build one or two at a university without everyone knowing. But 160, no freaking way.”

Perhaps I’m wrong, but I think you’re referring to fusion warheads. Fission bombs are set off by conventional high explosive, I think.

[GonzoGOP]

Perhaps I’m wrong, but I think you’re referring to fusion warheads. Fission bombs are set off by conventional high explosive, I think

No all warheads have to have a pit of highly enriched material. This is what causes the burst of neutrons that in turn sets off the chain reaction. It is what separates a reactor from a bomb. Some of our newer non-spherical ones have longer shelf lives, possibly as long as a century. But the ones from the kind of early cold war era bombs that a terrorist could get hold of tended to suffer from corrosion and decay over only a decade or two. The ones used on the Polaris missiles were particularly bad.

There is also a high probably that any pits for retired weapons had a lot of time on the clock when they went into storage. After all why manufacture a new pit for a weapon that you know will be taken out of service before the existing pit goes bad.

Finally they have to be stored under carefully controlled conditions or the decay will speed up rapidly. Looking at how Russia stored their nuclear subs I'm betting they didn't waste a lot of time on climate control system for parts of weapons that they never intended to use again.

Of course as many other posters have commented none of this applies to a dirty bomb. Any old radioactives will do for that purpose. But if you want that satisfying mushroom cloud effect you need to have all the right parts and have them in working order.

[NVDave]

A fusion weapon with a two (or three) stage design starts with lighting off what is essentially a fission weapon. The fission stage is set off by compressing a sphere of plutonium down, possibly boosted the neutron flux by injecting tritium into the pit. The resulting energy and force, channeled by “lenses” and reflectors, in turn becomes the crushing force and temperature rise to initiate the fusion reaction in the fusion fuel side of the weapon.

The fission trigger would be big enough to do significant damage to a city all by itself.