Hydrogen bombs actually require two fissionable critical masses, so that means at least 2-6 KG per warhead.
Your analysis of fusion bombs is completely wrong. First, a hydrogen bomb requires only one fissionable critical mass to compress the tritium-deutirium pit. Likewise, a fusion boosted fission device requires only a single fission charge. Finally, considering a fusion bomb is on the order of over 2-20X more powerful than a fission device while being not much heavier or larger than fission bombs, and as I already mentioned in a fusion bomb some fissile material is replaced with tritium and deuterium, you have reduced the amount of radioactive weapons grade plutonium.
Then there's neutron bombs detonated in the upper atmosphere to knock out missile guidance systems. They don't need two seperate fission charges.
Pure fusion devices, as their name implies, need no fission charge at all.
and for defensive purposes it makes no sense to go thermo-nuclear anyway, a .1 or .2 kt warhead is more than sufficient.
The purpose of these platforms is to possess the capability of annhilating every single thing in China from space. That's the 'defensive' role I had in mind. Which means multiple KT's at least.
Ejecting it? Sealing it in lead? If their is a failure, the delivery vehicle is going to explode and it is unlikely the material is going to be ejected,
And yet our shuttles have ejectable cockpits do they not? I wonder why that is...
It's called a contingency. Obviously a sudden catastrophic failure will render the ejection option useless, but any failure which would simply prevent the rocket from entering orbit, engine misfire or failure for instance, and thus fall to back Earth would not require that the rocket impact with it's payload still intact.