As far as the exploitability of fissionables as an industral resource is concerned, it is not the abundances that matter, but how those elements are concentrated by geological and geochemical processes. Aluminum, for example, is more abundant by weight than iron in earth's crust, but iron tends to collect in highly concentrated, massive recoverable mineral deposits. Iron is also easier to refine from ore. Iron is much cheaper than aluminum as a result.

The great variety of geological conditions and processes represented in solar system bodies may occasionally lead to very rich, easily recoverable quantities of very low abundance elements, or of those which are otherwise highly dispersed. Unfortunately, it is highly unlikely these bonanzas will all be located close to one another in dynamic space (locations mutually accessible with a minimum energy expenditure). The result is that these deposits may not immediately lead to a thriving solar system industrial economy. There will still be enormous costs associated with locating, mining, refining and transporting these commodities to sites where they can be integrated into manufacturing activity.

To put it another way, there may be a stack of highly enriched uranium ingots on the moon, but it would still cost too much, in dollars and Joules, to bring them to earth. And it would cost even more to haul to the moon the reactor components and industrial customers necessary to properly utilize them.