It seems like just the ticket to get a certain contingent on board. "The noble probe will remain stout and true; in the freezing depths of space it will be warmed by the Americium it carries in its heart."
I might be mistaken, (and someone please correct me if I'm wrong) but IIRC Plutonium is a side-product of the enrichment of weapons-grade Uranium. I think the non-proliferation of nuclear weapons treaty might impose some barriers on this process, and we're no longer in the Cold War, so it's kinda hard to get Plutonium.
Uranium enrichment is actually a physical rather than nuclear process, and thus it cannot produce other elements such as Plutonium. However once you have enriched enough uranium to create an operating reactor, its spent fuel will contain a few percent Plutonium. The problem is that only a few percent of that will be Pu-238, and separating that from the other four Pu isotopes is incredibly difficult, that is to say, economically intractable.
Therefore, the Pu-238 used in RTGs is likely produced through another process, neutron capture in Np-237. Np-237 is produced in very small amounts in a uranium reactor, but as it's the only Neptunium isotope produced in any significant quantity, there's no need to do an isotope separation on it. It can be chemically separated from the other elements in the spent fuel, which is much easier, although certainly still not easy.
In any case, with the end of the Cold War there are indeed fewer facilities willing & able to produce Pu-238 in kilogram quantities. In the US, spent fuel from commercial reactors currently cannot be re-processed at all, due to proliferation concerns.
Oh. Thanks for the detailed explanation and correction about the enrichment process. Do you think that once we have asteroid mining we'll be able to get Uranium (and consequently Plutonium) in higher quantities so that the economic costs will be viable again? That is assuming we can overcome the legal/security concerns by then.
That's a good question - AFAIK nobody has any real idea how much Uranium is present within nearby asteroids. Hopefully they will create some more RTGs & send some probes to find out!
