PREDICTIONS OF TRANSURANIC MOVEMENT IN SOILS
Attempts have been made to describe the movement of transSuranics
through soils on a mathematical basis.
Lester et al. (1974) investigated
the hypothetical band and
239,240bu (pCi/g), 225U and 258U (ug/g)
l
(that column which follows the
ground water flow path) to a surface water body from an underground
geologic nuclear waste disposal site.
Numerical resolutions of
analytical (mathematical) solutions revealed that differences in adsorption characteristics between soluble chain members, axial disper-
sion, and radioactive decay all act to reduce radionuclide discharge
rates at the exit of the soil column.
This method draws on a uniform,
one-dimensional model and requires evaluation cf the distribution co-
3
efficient, Kg. for each soil-radionuclide combination. Thus, this
technique has limited application to predicting movement of transuranics
in terrestrial soils where radionuclide Kg values can vary over wide
ranges along the transport path.
Other mathematical models to predict
the distribution of radionuclides in soils have been presented by
Cohen
(1975)
and Aleksakhin
(1963).
A direct application of predicting transuranic distributions
13.
jt tt LL
Distribution of
Area
L1-A Soil
1
239,240
(Adapted
a aera
£5 td
Pu,
2355,
in a soil
profile was presented by Jakubick (1976), who attempted to reconstruct
plutonium concentrations in soils of south-west Germany.
By correlating the few 733+?"°py measurements available in Germany with the fallout data from Ispra, Italy, the probable history of plutonium fallout
was reconstructed.
From these datathe plutonium input Funetion in the
vicinity of Heidelberg was derived. The plutonium distribution in a
soil column from fallout in the United States was used in conjunction
T
N
30
Fig.
0.1
oO
SOIL DEPTH (cm)
0]0.01
impulse releases of transuranic parent-
daughter chains through a soil column
with the calculated cumulative fallout input function to predict the
and
2
from Essington
3 By in NTS
et al.,
plutonium distribution and turnover rate in Heidelberg soils.
1976).
of this study imply that the migration of
Results
fallout plutonium takes place
completely, or to a great extent, in the form of discrete particles
probably weakly aggregated to soil particles. The removal of fallout
plutonium particles (analogous to plutonium oxide particles) from a
given soil layer seemed to obey an exponential law, with a characteristic turnover time of 5-6 years for a 5 cm thick partially saturated
soil layer.
.
DISCUSSION
This review has pointed out that there are many and diverse observations
of transuranic distributions in soils; however, almost ali of the observations are limited to plutonium.
Some information on the distribution of americium has been produced, but generally only at nuclear
weapons testing areas.
Measurements on the distributions of the other
69
68