M.S. Thesis Presentation by Momoko Goto
Monday, April 9, 2001

(Dr. Bernd Kahn, advisor)

"Development of a Quantitative Model for the Binding of Cesium to SRS Soils"

Abstract

137Cs is one of the major radionuclides found at the nuclear waste disposal sites. Because of its potential health risk to humans and the environment, a number of studies have been made on the development of models to predict mobility of radionuclides in soil.  Numerical methods have also been developed for simulating movement of some of the radionuclides.

It is found that the behavior of 137Cs does not fit the existing models.  Studies suggest that the edges of the clay particles (FES, Frayed Edge Sites) play an important role for the sorption of radiocesium. The mechanism of ion exchange at this site is still not clear.

The purpose of this study is to contribute to the development of a calculational model for radiocesium sorption to SRS soils. This study combined geological characterization and sorption/extraction study to understand basic mechanism of cesium behavior in the SRS soil.  For this purpose, 5 different soil samples were provided from SRS in different clay content (1% to 18%).

The geological characterization includes cation exchange capacity measurement, particle size analysis, and X-ray diffraction. From X-ray diffraction analysis, vermiculate-dominant sample characteristics were determined.  Sorption behavior was evaluated by using different concentrations of stable cesium (133Cs). Radiocesium (137Cs) partition was also analyzed. The relative capacity of FES was examined by using an agent to block exchange site.

Following the cesium sorption experiment, an eight-step sequential extraction was performed to determine the chemical condition of bound cesium.  Based on these findings, possible factors for a proper simulation model were discussed.