Appendix A
DOE-HDBK-1015/1-93
BASIC SEPARATION THEORY
Rev. 0
CH-01
Page A-1
BASIC SEPARATION THEORY
Introduction
The fundamental principles upon which a gaseous diffusion plant is based are as follows.
1.
All the particles (atoms, molecules, or ions) which make up the gas are
continuously moving in straight lines in all directions. The particles collide
with anything in their path (e.g., other particles or the walls of the container),
thereby altering the course of moving particles but not their average velocities.
2.
All of the particles have the same average kinetic energy. Accordingly, if the
masses of the particles are different, so must their velocities be different with
the lighter particles having the greater average velocities.
On the basis of the two principles stated above, if a quantity of gas is confined by a porous
membrane or barrier, some of the gas will escape through the pores in the barrier. If the
confined gas is isotopic (a mixture of particles of different molecular weights), the lighter
particles of the gas will have a greater tendency to diffuse through the barrier because of their
greater average velocities. Consequently, the gas which has passed through the barrier will
be enriched in the light constituent while that gas which has not diffused through the barrier
will be depleted in the light constituent.
Isotopic Separation
The isotopes with which we are concerned are those of uranium; namely U
and U
. In
235
238
order that the isotopes of uranium may be separated by the gaseous diffusion process, it is
necessary that the uranium be in a gaseous state. This is accomplished by combining the
uranium with fluorine to form uranium hexafluoride, which is a gas at workable temperatures
and pressures. Another advantageous quality of uranium hexafluoride is that fluorine has no
isotopes to further complicate the separation process. In general, the following discussion
is concerned with the separation of U
F and U
F .
235
238
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