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