MOVEMENT OF URANTUM
Although uranium is not a transuranic, certain uranium isotopes in the
nuclear
fuel cycle have been identified as potentially hazardous and
Table 3.
Warrant discussion.
233
Assumed Radioactivity of Uranium Isotopes
233
in 1 gram of
U Fuel
232
Till (1975) discussed the recycle aspects of
U bred from
Th in
the High Temperature Gas-Cooled Reactors. The recycle 773u can contain
up to 1200 ppm 232u
which was stated
a relatively high specific activity,
total
772-2344 radioactivity.
various uranium isotopes
to be very radiotoxic,
and as accounting
Table 3
in 1 ¢ of
lists
as having
for 82.1% of
the
the assumed activities of
233y fuel.
It can be seen that’??? u
can account for greater than 50% of the total uranium activity present.
Because of the potential environmental hazard of 7??U,
of uranium migration
through soils
is
an evaluation
in order.
Natural uranium is distributed throughout minerals and sediments
world over.
Hansen and Stout
(1968)
the
noted that uranium and thorium
appeared to accumulate in soils as a result of rock weathering and soil
formation.
the
Maximum natural
"B" horizon, whereas
thorium concentrations
tended to be
themaximum uranium concentrations were most
are highest in the soil clay
fractions;
however,
Hansen
{1970),
in a subsequent study,
suggested
recycle activity
fraction
(ci)
232),
001
2.14 x 10°?
233)
613
5.82 x 109
234),
.243
1.51 x 103
2355)
080
1.72 x 1077
236,
.063
3.99 x 1076
Adapted from Till (1975).
that 600,900 years after initial deposition, most of the nuclides of the
uranium and thorium
families
are
in
the
finer
textured soil
fractions
and that the uranium that is retained by the soil is more likely to be
fixed
in some
immobile
form.
Probably the only literature citation revealing uranium migration in
environmental soils on a short-time basis was presented by Essington
(1976).
During the nuclear testing program discussed earlier in the
section entitled
"Safety Shot Sites,"
there was an explosive
test of
235y enriched nuclear device.
A soil profile taken from near the
round zero area (Fig. 13) showed the vertical distribution of 239,260 Pu
38 levels reflected the natural concentrations
The
aey, and 7?5y,
However, when 235y was disin the mineral structure of the soil.
tributed over the soil surface it did migrate into the soil pro-
file as evidenced by the 735y distribution.
to behave very much like
the same time.
239,240n,)
Equilibrium
recycle atom
clays
developed from carbonate rich soils show relatively low uranium and
thorium concentrations.
Isotope
in
often in the topsoil.
This suggests that thorium moves down the soil
profile more rapidly than uranium.
Generally, uranium and thorium
concentrations
Equilibrium
This added ??*u appeared
also distributed at approximately
66
67