Try uranium dust, thorium dust and plutonium dust though, if you are not running nuclear reactors. Especially plutonium, it is the most potent amplifier possible. One piece of dust is equal to 400 scrap I believe (it will produce 12 UU-matter by itself). Uranium is still half as good.
And since the standard recipe for Plutonium dust is 1 uranium dust + 1 UUM... Exploit that and your 6-UUM Uranium becomes worth 11 UUM.
I wind up using Thorium most of the time though because I wind up with more of it than I know what to do with.