Oh dear oh dear oh dear. Where do I start?
I highly recommend Command and Control by Eric Schlosser. It's an account of American nuclear safety and policy through the Cold War. It's an excellent, if somewhat alarming read.
There was a lot that could and nearly did cause a nuclear disaster, especially when they were being flown around by bombers, at least until saner, safety minded people finally prevailed and forced better safety standards.
What precisely could have gone wrong?
- The X-Unit (a kind of power discharge device used to detonate the explosive 'lens' that set off the bomb) could accidentally be charged by a short circuit or old cabling. From there only a minor additional issue of any kind could have caused discharge and detonation.
- An error in (manual!) assembly could have easily triggered the detonator in older nuclear weapons
- Dummy 'training' nukes were stored right next to real nukes. Pre-assembled nukes of course had real atomic cores integrated into them.
- Nuclear weapons were designed in such a way that a fire could cause safety features to be bypassed because of wires being close together.
Now it's our good fortune that this hasn't caused a nuclear accident to date but of the 32 broken arrow incidents to date any one of them could have ended in nuclear fire - many over US territory!
So yes, it's entirely realistic and it wouldn't be all too distant a world in which we look back and ask 'is there a world where we never had a nuclear accident'
Today's nuclear weapons are much safer by design, of course - a product of a great deal of hard work by many people - but it's not too hard to see how we could be back to that level of (hidden) risk.
In 2011, some technicians at the Los Alamos nuclear laboratory decided it would be neat to pose 8 plutonium rods for a photo op. They were close enough that reporters clustering around to take photos would have caused a criticality incident (from their bodies reflecting neutrons), killing everyone in the room. As it was it was realised and carefully defused in time. The safety team walked off the job in disgust afterwards, and to this day the lab still hasn't been able to satisfy safety checks and remains closed.
It's no effort at all to imagine a world not too far from now where growing political pressures and global instability have led to the development of new weapons. Where concerns about the ability to guarantee their detonation overrides concerns over how to prevent it. A new missile, built without the hard-won lessons of the nuclear age, 24/7 alertness drills, a miscommunication to an operator in Hawaii...
It would be all too easy.