PLENTIFUL ENERGY

Whether or not a given reaction can occur, and if it can, how completely, depends
on the magnitude and sign of these differences.
Table 9-1. Free Energies of Chloride Formation at 500 o C, - kcal/g-eq*
Elements that remain
in salt
(very stable chlorides)
BaCl 2 87.9
CsCl 87.8
RbCl 87.0
KCl 86.7
SrCl2 84.7
LiCl 82.5
NaCl 81.2
CaCl 2 80.7
LaCl 3 70.2
PrCl 3 69.0
CeCl 3 68.6
NdCl 3 67.9
Elements efficiently
electro transported
CmCl 3 64.0
PuCl 3 62.4
AmCl 3 62.1
NpCl 3 58.1
UCl 3 55.2
Elements that remain
as metals
(less stable chlorides)
ZrCl 2 46.6
CdCl 2 32.3
FeCl 2 29.2
NbCl 5 26.7
MoCl 4 16.8
TcCl 4 11.0
RhCl 3 10.0
PdCl 2 9.0
RuCl 4 6.0
YCl 3 65.1
*The term kcal/g-eq is to be read as kilocalories per mass in grams of the material
interacting with one mole of electrons. (For elements with a valence of one the
mass is just the atomic weight in grams; for trivalent substances, uranium for
example, the mass is one third of the atomic weight; and so on.) The sign of the
numbers is understood to be negative.
Three groups of chlorides can be identified, separated in free energies of
formation. Each acts differently. The first group is the active metals, which stay as
stable chlorides in the electrolyte until they are stripped out in later waste
processing. The second are the uranium and transuranics, which electro-transport to
the cathode of the electrochemical cell, the only elements that are actually
―electrorefined.‖ They are the product. The third are the metals with still less stable
chlorides, iron and the noble metals particularly, which do not form stable chlorides
in the presence of more active elements; they collect as metals in the cadmium pool
below the electrolyte or remain as hulls in the anode basket.
Thus the first big separation of product from waste comes directly from chemical
reactions of the spent fuel ions with less stable chlorides—uranium chloride
principally—in the molten salt. For the elements left in the anode, their nonreaction
serves a similar purpose. Most of these separations, important as they are,
have little to do with the imposed voltage. They are due solely to the energy
relationships basic to the elements themselves. They cause reactions which leave
most of the troublesome fission products in the salt, others in the liquid cadmium
below the salt, and still others, non-reacted, in the anode basket. The imposed
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