A program to examine the soil-actinide relationship in sediments from a disposal facility was initiated in March 1973. Initial work has been done using samples from the 216-Z-9 covered trench. Soil mounts were made of soil recovered from a core of an uncontaminated well drilled alongside Z-9 trench. The mounts were made by plastic-impregnating smaller, 1-in. diameter cores taken from the original 4-in. diameter cores. The uncontaminated mounts showed that the less than 30 mesh soil was composed of predominately metamorphic rock fragments of the Belt Series, brought down from northern Washington and Idaho by the ancestral Columbia River. Two 4-in. diameter cores, 2 ft in length. were taken from the floor of Z-9 trench. Smaller contaminated mounts were made from these original cores in the same manner as with the uncontaminated samples. Overlying one of these cores (4-- 11), was a sludge layer of silica, alumina and water. The other core (4-5) had no sludge layer. At least two types of plutonium were found in cores 4- 11 and 4- 5 by autoradiographic and microprobe examination. The plutonium particles (up to 10 mu m in diameter and 60 wt% PuO/sub 2/) were the most conspicuous form. These occurred near the top of the core 4- 11, but extended down nearly to the bottom of core 4--5. It is probable that the sludge layer over core 4-11 acted as a filtering media to remove and concentrate the plutonium particles. The second form of plutonium occurred in lesser concentration (<0.4 wt% PuO/sub 2/) but was found throughout the lengths of both cores associated with silicate hydrolysis. Silicate hydrolysis was investigated with microprobe chemical analysis. Loss of alkalies and alkaline earths, along with the absence of several metamorphic minerals found in the uncontaminated mounts, indicated extensive chemical attack of soil rock fragments by acidic influent solutions. The locations of the base of the silicate hydrolysis zone, and associated plutonium deposition, are presently unknown. (auth)
Experimental radionuclide distribution coefficients (Kd') were determined for Pomona, Flow E, Umtanum basalts, and secondary mineralization associated with Pomona basalt at 23/sup 0/, 60/sup 0/ and 150/sup 0/C. Radionuclides used were /sup 75/Se, /sup 85/Sr, /sup 99/Tc, /sup 125/I, /sup 135/Cs, /sup 226/Ra, /sup 237/Np, /sup 238/U, /sup 241/Am, and /sup 241/Pu. Solution oxygen contents were controlled by the basalt/groundwater system (Eh = 600 to 700 mV), and were high (8.2 to 8.4 mg/l) at 23/sup 0/C. Oxygen contents and pH changed little in contact with basalt. The effects of temperature changes on radionuclide Kd' results varied depending upon the radionuclide involved, solution-solid reactions, and the relationship of the radionuclide to these reactions. For example, cesium Kd' values decreased from 3100 ml/g for Umtanum basalt at 23/sup 0/C to 120 ml/g at 150/sup 0/C. At the same time, strontium Kd' values increased for Umtanum basalt from 105 ml/g at 23/sup 0/C to complete removal at 150/sup 0/C and 40 days. Radionuclide adsorption coefficient measurements at higher temperatures and pressures were made in addition to the 23/sup 0/C, solution-solid contact time-conditional Kd (Kd') measurements. These include Kd' measurements with Umtanum basalt, Pomona basalt, Flow E basalt and secondary mineralization and radioisotopes of americium, cesium, iodine, neptunium, plutonium, radium, selenium, strontium, technetium and uranium. The additional temperatures involved were 60/sup 0/C, 150/sup 0/C, and 300/sup 0/C. At 150/sup 0/C, argon pressures of 6.9, 13.8, 20.7, and 27.6 MPa will be used to ascertain the effects of pressure changes on Kd' values. So far only the 6.9 MPa argon pressure has been investigated. The upper temperature of 250/sup 0/C is where thermal breakdown of dioctahedral smectites (secondary mineralization) begins.
Data on the kinetic anion replacement systems calcite-PO 4 (super -3) , calcite-F (super -) , gypsum-CO 3 (super -2) , and gypsum-PO 4 (super -3) are given, along with concomitant Sr (super +2) inclusion into the final product. In a system containing several anions, only the anion forming the least soluble compound with the available cation is stable. The replacement reaction rate is directly proportional to the solubility difference between the original solid and final product. Several other variables also affect the reaction rate including temperature, column flow rate, influent pH, surface area of the initial solid, concentration of extraneous ions, and concentration of active anion. These variables affect diffusion rates to and from reaction sites as well as differences in solubility between initial and final reaction products. The crystal structure of the resulting product greatly affects the concomitant removal rate of Sr (super +2) into the resulting product.
A proposal that cation selectivity of zeolites is mainly a function of anionic site separation distances was tested with high and low silica-to-alumina ratios of the same zeolite crystal structure (faujasite and Type A). Anionic site separation distances of the high silica zeolites were assumed to be relatively greater than the low silica zeolites. The high silica zeolites were considerably more cesium-selective from a sodium-cesium system than the lower silica zeolites, as expected. Strontium selectivity from a sodium-strontium system was generally greater with the low silica zeolites, but was complicated by anionic site separation distance heterogeneity.
The sorption behavior of selected radionuclides on the Columbia River basalts has been investigated. Radionuclide distribution coefficients, using a batch-equilibrium technique, have been determined for iodine, selenium, technetium, strontium, cesium, uranium, radium, plutonium, americium, and neptunium. Since the distribution coefficient value is an empirical value, the effects of temperature, pressure, groundwater composition, and Eh conditions on the distribution coefficient value for these isotopes have been investigated. In addition, sorption isotherms, describing the dependence of radionuclide sorption on radionuclide concentration for cesium, strontium, radium, plutonium, and uranium (under both oxidizing and reducing conditions) have been determined. Based on these sorption data, it appears that, under the expected ambient repository conditions (e.g., reducing, alkaline conditions), the Columbia River basalts are capable of strongly retarding cesium, strontium, radium, and neptunium migration and moderately retarding uranium, technetium, and plutonium migration. The basalts are not capable of significantly retarding the migration of iodine and selenium.
Cation exchange equilibria in binary systems of Cs/sup +/, Sr/sup 2+/, or Ce/sup 3+/ with other cations expected in fission product recovery solutions are presented for several zeolites (Linde 4AXW, 13X, AW-400, AW-500, Norton Zeolon, and clinoptilolite) along with a method of estimating zeolite loadings for multication systems. Strontium breakthrough curves are calculated from equllibrium and diffusion data for comparison with experimental breakthrough curves. Cesium and strontium loadings of about 1.5 and 2.5 meq/g of zeolite, respectively, were obtained with cesium and strontium feed solutions. Column results show 0.9 and 1.3 meq/g of cesium and strontium, respectively, loaded together on 4A from a simulated CSREX IBP solution. (auth)
