> Another consideration is cost. Nuclear weapons are expensive to make, so a design that can get a high yield out of a small amount of fissile material is preferred. Maintenance, and the cost of maintenance, is also relevant. Will the weapon still work in 30 years, and how much money is required to ensure that?

I've seen speculation that Russia's (former Soviet) nuclear weapons are so old and poorly maintained that they probably wouldn't work. Not that anyone wants to find out.