PLENTIFUL ENERGY

product chlorides are highly stable; they go to the electrolyte and they stay there.
Later in our process they are processed as waste.
The least stable, with the lowest free energies, are the metals themselves:
cadmium, steel cladding, the alloying zirconium, and the transition metals normally
used as structural materials, characterized by high strengths, high melting points
and high boiling points. They are never in the salt. Low in stability as a chloride,
these metals remain metals throughout. They remain in the anode basket or in the
liquid cadmium layer below the salt.
In the middle group are the fuel isotopes (zirconium to some degree may be
picked up too) and a few rare earths. They exist as chlorides in the electrolyte, the
elements to be electro refined.
Uranium is deposited on a steel cathode as a dendritic (with tentacles) deposit,
quite pure, with some adhering salt. Plutonium and the other transuranics, in the
presence of uranium chloride, will not deposit that way. Their stability in chloride
form is greater than that of uranium chloride—that is, their free energies are more
negative than uranium. So instead of depositing as metal at the cathode, they
immediately react with the uranium chloride and form their more stable higheractinide
chlorides once again. Thus, when reduced, they just exchange right back
into the electrolyte as chlorides. In the presence of ample uranium chloride, as is
normally the case when electrorefining the bulk of the uranium, they cannot be
collected this way.
If they are to be collected, something must be done to change the free energy
relationships. Or, possibly (and there is some evidence for this), the higher actinides
might be collected on a metallic cathode by allowing the voltage to increase to pick
up the higher actinides, after reducing the uranium chloride concentrations very far
below the concentrations of higher actinides in the electrolyte. Uranium, if present
at all, would still appear in a substantial amount in the product, and the higher
actinides would come as a group.
The IFR process must use both effects to collect plutonium and the higher
actinides—that is, both altering the free energies and reducing uranium chloride
concentrations. Free energy relationships are altered by use of a liquid cadmium
cathode instead of solid steel. The higher actinides as metals form compounds with
the metal cadmium, ―intermetallic compounds,‖ whose effect is to lower the free
energies of formation of chlorides by the amount of free energy used in forming the
intermetallic compound. The free energies of the intermetallic compounds then
almost match that of uranium itself; they do remain higher, but only slightly. The
intermetallic compounds stabilize the higher actinide elements in the cadmium. In
this way, by using the two different cathode types, it is possible to separate
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