PLENTIFUL ENERGY

and the very reason for the process. They become fuel once again—to be recycled
back into the reactor. If left in the waste, however, they would be the principal
contributors to the long-lived toxicity of nuclear waste. 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 merely collect
as metals in the cadmium pool below the electrolyte, or remain as hulls in the anode
basket.
Table A-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
SrCl 2 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 terminology kcal/g-eq is to be read as kilocalories per mass in grams of
material interacting with one mole of electrons. The sign of these numbers is
understood to be negative.
Note that the fission products, which are the great majority of elements in the
electrorefiner, whether above or below the actinides in free energy, are not touched
at all by the refining process. Their chemistry isolates them and enables them to be
recovered and processed later as waste. The chloride compound electrolyte was
selected specifically for this reason: It provided the distinct separations necessary to
the process.
The chlorides with the greatest free energy of formation (that is, the highest
negative numbers in the table) are the alkali metals—lithium, sodium, and,
significant because of its radioactivity, cesium; the alkali earths, beryllium and so
on; and significant also for its radioactivity, strontium. Strontium and cesium are
the most troublesome of the fission products. Their radioactive isotopes are created
in quantity, they have penetrating gamma rays, and their half-life is a few decades,
assuring they will be around for quite a while—a few hundred years, in fact—and
radioactive in quantities high enough to be concerned about. But these fission
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