Determination of the Factors Controlling Colloid Generation from Altered Waste Forms: TEM Study of Colloid Interactions and Fractal Structure
EMSL Project ID
2378
Abstract
The purpose of this work will be to determine the factors controlling the release of colloids from an altered waste form. These factors include; temperature, ionic strength, pH, and flow rate. Experiments will be carried out that will look at the behavior of non-radioactive simulated colloids (see Table 1 for composition of starting material) and their interaction with iron oxy-hydroxides and smectite clays. We will use TEM to investigate the microstructure and composition of these particles. This experiment is described in greater detail in document, ?Determination of the Factors Controlling Colloid Generation from Corroded Spent Nuclear Fuel,? submitted to the Yucca Mountain Program. Colloids behave as fractal objects with aggregation either diffusion or reaction limited. The fractal dimension will influence the activation barrier for release; hence, knowledge of the fractal dimension will provide an indication of the probability of release. Many corrosion tests under accelerated reaction conditions, result in changes in the fractal dimension of precipitated products in the alteration layer. This will change the activation energy barrier for release and, hence, the release kinetics of particles from the corrosion rid under either continuous or intermittent flow conditions. The nature of the corrosion rind of the pre-test material needs to be studied in order to understand the mechanism of primary colloid release. Small angle neutron or x-ray scattering can be used to determine the fractal dimension (df) of a corroded solid material. TEM or light scattering can be used to look at df in colloids from a solution. Fractal objects are those whose structure remains self-similar under a change in scale [ZHANG-1996]. A portion of the aggregate is statistically equivalent to the structure of the entire aggregate. This leads to a power law relation between the mass, m, and the dimension of the portion of the aggregate, l, as : m = a ldf (7) Where a is a constant depending on the topology of the aggregate and df is the fractal dimension. Utilization of the fractal concept can improve the ability to describe the structure of any colloidal aggregates from the columns and their formation mechanisms [ZHANG-1996; LIU-1990]. The nature of colloid aggregation can be investigated by studying images of colloids obtained with TEM. The fractal dimensionality (df) depends on the nature of the aggregation process. When aggregation is diffusion limited, where particles attached irreversibly at contact, the structure is less dense and df is small. If a potential barrier must be overcome the resulting colloidal aggregate will tend to be more dense with a higher df. The higher the df in the starting colloidal materials in the column, the lower the potential for release of particles. Hence, the df could be a useful measure of the release potential of a type of particle. Composition of Proposed Simulated Residue for RE Tests Compound wt% SrO 5 Nd2O3 15 La2O3 10 Sm2O3 5 CeO2 10 SnO2 30 TaO2 15 ZrO2 15 Total 100 High magnification imaging, electron diffraction, and electron and x-ray spectroscopic techniques will be used to determine the morphology, structure, and composition of released particles. This information will be used to support interpretation of colloid behavior and be used as input to colloid calculations. Various software packages (Gatan DigitalMicrograph, EL/P, and Oxford ISIS) will be used to interpret the data.
Project Details
Project type
Exploratory Research
Start Date
2001-11-01
End Date
2004-11-02
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Buck EC, pA Finn, and JK Bates. 2004. "Electron Energy-loss Spectroscopy of Anomalous Plutonium Behavior in Nuclear Waste Materials." Micron 35:235-243.