Hilmar,

I don't remember the specific numbers anymore but it's at least 10 to 100 times easier to fuse a deuterium and tritium nucleus or two deuterium nuclei together than it is to fuse 4 hydrogen nuclei together. The separation process for deuterium is a lot easier than it is to separate U₂₃₅ from U₂₃₈ because of the difference in the relative weight of the atoms.

>That is, assuming that only deuterium is used. I suspect that eventually fusion technology will develop so far that H(1) can be used - as it does in the Sun. I read somewhere that on Earth, there is about one deuterium atom for every 5000 H(1) atom.