rate, because a large particle diameter relative to
column diameter might introduce random pertur-
bations into the experiment. Accordingly, we determined specific flow rates for columns of three
diameters packed with two lots of sand that differed
in particle size distribution. We found thatin 5-, 10-,
and 25-mm-diam columns packed with 38- to 147um sand particles on the one hand and 350- to 600um sand particles on the other, the specific flow
rates differed by no more than 10°relative standard
deviation when calculated in termsof milliliters per
second per square millimeter for the average particle
cross-sectional area. These experiments also included 110- and 140-mm waterheads on the columns. We
concluded that the specific flow of water through
these columns was independentof the column waterhead and diameter, as long as the particle diameter
did not exceed 10°¢ of the column diameter and the
waterhead did not exceed 50% of the soil height.
In the plutonium absorption experiments, we
packed six 25-mm-diam columnswith silt loam that
had been sieved to removeparticles larger than 0.8mm diam. This soil is about 60% silt, 25°; sand, and
15% clay. Its bulk density is 1.07 g/cm’: its particle
density, 2.70 g/cm®. It has a total porosity, ¢, of 60.3,
as calculated from the bulk andparticle densities us-
ing the relation
.
€ = 100(1 —D»,/D,).
Three columns, 100-mm-high, have retained
greater than 99.8°- of the plutonium from the feed
solutions during 474 days of operation. Differences in
flow rates from 1.1 to 0.027 ul/s among the three
columns have not affected the retention of
plutonium significantly. The other three columns
are 250-mm high and contain soil sieved to remove
particles smaller than 52 um in order to achieve
more uniform flow rates. After 282 davs of operation,
the fastest flowing column, with a rate of 2.7 ul/s, has
retained 99.67°: of the plutonium, and the other two.
with flow rates of 1.3 and 1.8 “l/s. have retained over
99.9° of the plutonium from their feed solutions.
The concentration of the plutonium in the feed
solutions is approximately 1 ug/l.
V. BEHAVIOR
OF
ENVIRONMENTS
*8py
IN
AQUATIC
(George M. Matlack, Gilbert B. Nelson, James H
Patterson, and Nicholas Vanderborgh)
The behavior of 79Pu fuels in fresh water and
seawater, especially rates of plutonium release, is
being investigated in aquaria and in natural sea environments. Although the solubility of hydrated
PuQ, is extremely low, corresponding to about one
atom of plutonium in 100 000 liters of water at pH 7,
other interactions between water solvent systems
and typical 78Pu fuel can release plutonium at a low
but finite rate. Measurements of these release rates
from variousfuels in differing circumstances provide
data for assessing the risk to the biosphere from fuel
container failure in the ocean or in fresh water, and
for devising means to prevent unacceptable risks.
A. Seawater Aquarium Experiments.
Each 94-liter aquarium contains 75 liters of
simulated seawater, made by dissolving a commer-
cial mixture of salts in distilled water, and maintained at pH 8.1 to 8.3. A refrigeration system keeps
the water at 10°C when a 40-W heat source is immersed in the water and the room temperature is
25°C. Water is circulated by an air bubble stream
behind a baffle in each rear corner. Each aquarium
has acover sealed at the sides with silicone rubber
cement to contain airborne plutonium. Water
samples are removed through a small hole in the
cover.
B. Ocean Test Facility.
Samples in specially designed steel chambers are
submerged in 25 m of seawater off San Clemente
Island, 100 km west of San Diego, at a Naval
Undersea Center facility. Each chamber is approximately 50 cm in diameter and 25 cm deep. and
the inside is covered with an asphaltum-like coating.
The chamberis weighted on the bottom by a circular
slab of concrete. The open top is protected by a conical metal canopy about 60 cm high. Water can
enter only through the perforations in the canopy.
wd
A preliminary requirement was to determine how
the soil column diameteraffected the specific flow
“om
eo:
oo
sor
a
11