Characterization of actinide bearing soils: top sixty centimeters of 216-Z- 9 enclosed trench

Abstract

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 nearmore » 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) « less

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