PLENTIFUL ENERGY

electrochemical reaction, and once the electrons are dislodged they go through the
rest of the electrical circuit outside the cell, via a power supply and wiring, to the
cathode. Simultaneously, by a matching electrochemical reaction at the cathode, the
electrons, negatively charged, are consumed by the positively charged actinide ions,
converting them back to metals again. Then they deposit as metals on the cathode.
The two electrochemical reactions are the mechanism for transferring electrons to
and from the metal ions across the boundaries formed by the electrode surfaces. In
this way the electrical circuit is completed.
Typically the current is controlled and made as high as possible, because current
is a direct measure of the product stream. But it is subject to a cutoff to stop the
voltage from rising high enough to start to transport other elements as well.
The spent fuel constituents, once dissolved, distribute throughout the
electrorefiner. Some stay in the anode basket; some deposit on or in cathodes,
depending on the cathode design; some stay fixed in the electrolyte itself; and some
go to the layer of liquid cadmium in place below the electrolyte. Where, and in
what concentrations, things go in the electrorefiner is an important matter. The
ability to calculate this, even approximately, is important to understanding and
optimizing the process. It is done by making a simplifying assumption: that the
elements reach an equilibrium distribution in the electro-refiner. The process can
then be analyzed and further optimized on this basis.
For the equilibrium assumption to hold (approximately), it can be seen that the
reactions of the metals from the anode with the electrolyte salt, ionizing them, must
be rapid enough to dominate over the processing rates themselves. In development,
therefore, it was postulated that the various elements do distribute in concentrations
approximately those of equilibrium, and subsequent measurements have shown this
to be so, at least to the precision of the measurement techniques. The concentrations
of elements in the various parts of the electrorefiner are now calculated with useful
precision.
A.3 Principles of Electrorefining: What Are the Basic Phenomena
Here? What Is Fundamental?
Atoms, ions, electrons, and molecules are the fundamental particles—but the
bases of our process go no deeper than the molecular level. Chemical reactions are
in fact just these very small particles interacting (colliding) with each other. Tiny
energy changes occur in these interactions, and the energy changes determine what
happens in the process. Quantum theory is needed to accurately describe properties
of particles as infinitesimally small as these, but we need deal with such theory only
in the most cursory way for an understanding perfectly adequate to our purposes.
346