How soluble is uranium in molten iron? As I know, uranium and iron simply aren't mixable, which means there are no U-Fe alloys. The Google says, uranium is insoluble in molten iron.

But, if something is "insoluble", it actually means only that there is a very low maximal concentration.

What if we want to mix only 1ppm of U in molten Fe? What if 0.01 ppm? What is the maximal concentration?
According to Uranium partitioning between liquid iron and silicate melt at
high pressures: implications for uranium solubility in
planetary cores


  The solubility of U in
  liquid Fe is in the range of 0.6 to 800 ppm and increases with temperature (T) and
  pressure (P).


See also U solubility in Earth’s core which finds a solubility of 2 ppm at zero pressure (run number 198).