SESSION I DISCUSSION
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nisms of their release, transport, and deposition. We have developed
a model which predicts fission-product fractionation and which gives
satisfactory agreement with data from the in-pile experiments in which
we have melted UO, fuel elements. The data are plotted in a manner
identical to that of Dr. Freiling and his coworkers, with a straight line
being obtained. Our theoretical analysis shows that the slope of the
line is a simple function of the heats of vaporization of the fractionating species. The intercept of the line can be calculated from information on the total inventory of the material vaporized. We have performed
this type of analysis for all our own in-pile experiments as well as for
the experiments of other researchers in the field of nuclear safety.
These include experiments on fission-product release by postirradia-
tion annealing below the melting point of the fuel, by melting fuel under
varying conditions, and by operating reactors. We also were able to
predict the slopes in fair agreement with those measured by Dr. Freiling and reported in his published work on nuclear debris. Our theory
is described in USAEC Report ORNL-3547, which is an Oak Ridge National Laboratory Nuclear Safety Semiannual Progress Report. We
call the model the vapor-transpiration model because in our own
experiments we feel that fractionation is actually taking place at the
time that the fission products are vaporized from the fuel. Characteristics, such as particle size, of the subsequently condensed aerosol
serve to spread out the released fission products so that they can be
sampled at various locations in the experiment. Our theoretical analy-
sis of Freiling’s data treats fractionation as occurring during condensation of the debris from nuclear weapons.
FREILING: Thank you very much, Dr. Miller. It is gratifying
to hear that the considerations of fallout are also applicable to reactor
work, and we hope that they will also be applicable to the medium in
between these two extremes, namely, destructs of NERVA reactors
by one means or another and the resulting production of nuclear debris.
I would like to think of and refer to nuclear debris instead of fallout to
keep our thinking broad on this subject. [Editor’s Note: In the AEC’s
Atmospheric Radioactivity and Fallout Research Program, the term
“vadioactive fallout” is defined to include any atmospheric radioac-
tivity, irrespective of source. Hence, the specification for this conference that the papers presented be limited to fallout from tests of
nuclear weapons. |