fissile

And all the material created by natural fission decay of fissile materials in the Earth's crust and elsewhere...

These isotopes are extremely difficult to separate, and more cost-effective ways of obtaining fissile material exist (e.g.

Every single gram of fissile in the world's nuclear weapons was made in a thermal reactor or enriched from ore.

Importantly, non-fissile isotopes such as U-238 are continually recycled so that no energy is left unextracted.

And if you have a critical mass of fissile materials, you can create a nuclear bomb.

If you can produce a breeder reactor in a garden shed, you can eventually obtain a critical mass of fissile materials.

The hardest part is acquiring the fissile materials, which turns out to be slightly tricky.

They are still overgrown 1950s submarine reactors that only make use if about 3% of the useful energy in fissile fuel.

I think you mean fissile instead of fissionable [1].

The hard part is enriching the requisite quantity of a fissile material.

The degradation of the fissile material as well as its surroundings is highly critical to a nation's security, and also very hard to model well.

Most of the radioactivity danger from nuclear weapons and reactors relates to the byproducts of the fission process, rather than to the original fissile material.

Because of the speed and strength of the "radiation implosion" (though strictly speaking it's a radiation powered ablation implosion) the amount of fissile material can be small compared to a chemically powered implosion design (keeping in mind that critical mass goes down as density goes up).