The effects of various solution chemistry parameters on the alteration and leaching characteristics of a copper borosilicate simulated waste glass have been determined under hydrothermal conditions. Results are presented which demonstrate that leachant salinity, volume/glass surface area ratio, pH, cation content, and dissolved SiO2 concentration effects are important. A brief explanation of these results is given which is based on ion exchange and solution saturation equilibria.
The chemical durability of simulated nuclear waste glasses having different water contents was studied. Results from the product consistency test (PCT) showed that glass dissolution increased with water content in the glass. This trend was not observed during MCC-1 testing. This difference was attributed to the differences in reactions between glass and water. In the PCT, the glass network dissolution controlled the elemental releases, and water in the glass accelerated the reaction rate. On the other hand, alkali ion exchange with hydronium played an important role in the MCC-1. For the latter, the amount of water introduced into a leached layer from ion-exchange was found to be much greater than that of initially incorporated water in the glass. Hence, the initial water content has no effect on glass dissolution as measured by the MCC-1 test.
For isolation of nuclear wastes through the vitrification process, waste slurry is mixed with borosilicate based glass and remelted at high temperature. During these processes, water can enter into the final waste glass. It is known that water in silica and silicate glasses changes various glass properties, such as chemical durability, viscosity and electrical conductivity. These properties are very important for processing and assuring the quality and safety controls of the waste glasses. The objective of this project was to investigate the effect of water in the simulated nuclear waste glasses on various glass properties, including chemical durability, glass transition temperature, liquidus temperature, viscosity and electrical conductivity. This report summarizes the results of this investigation conducted at Rensselaer during the past one year.
The Symposium on the Scientific Basis for Nuclear Waste Manage ment was held in the fall of 1979 in Boston, Massachusetts and was one of a number of symposia included in the Annual Meeting of the Materials Research Society. The thrust of this annual Symposium is unique in the area of waste management. Recognizing that this is an area of great complexity which requires contributions from scien tists with many different backgrounds some of which are not normally associated with nuclear energy, the Materials Research Society pro vides a forum for discussions of a wide range of materials behavior and transport phenomena. As can be seen from the list of references in each paper, the authors draw heavily on contributions associated with professional societies in addition to the Materials Research Society, and this annual meeting encourages the cross-fertilization between disciplines that are essential to an adequate treatment of the problems associated with nuclear waste management. The proceed ings of the first Symposium that was held in 1978 was designated as Volume 1 in this series. The third Symposium is scheduled for 1980. The scope of the 1979 Symposium was guided by the Steering Committee: R. L. Schwoebel, Sandia Laboratories, USA (Chairman) W. Carbiener, Battelle Memorial Institute, Columbus, USA D. Ferguson, Oak Ridge National Laboratory, USA W. Heimerl, DWK, Mol, Belgium W. Lutze, Hahn Meitner Institut, Berlin, W. Germany J. D. Mather, Institute of Geological Sciences, Harwell, UK G. Oertel, Department of Energy, USA R.
The effects of groundwater chemistry on glass durability were examined using the hydration thermodynamic model. The relative durabilities of SiO2, obsidians, basalts, nuclear waste glasses, medieval window glasses, and a frit glass were determined in tuffaceous groundwater, basaltic groundwater, WIPP-A brine, and Permian-A brine using the monolithic MCC-1 durability test. For all the groundwaters, the free energy of hydration, calculated from the glass composition and the final experimental pH, was linearly related to the logarithm of the measured silica concentration. The linear equation was identical to that observed previously for these glasses during MCC-1 testing in deionized water. In the groundwater-dominated MCC-1 experiments, the pH values for all the glasses tested appeared to be buffered by the groundwater-precipitate chemistry. The behavior of poorly durable glasses demonstrated that the silica release is a function of the ionic strength of the solution. The ionic strength, in turn, reflects the effect of the groundwater chemistry on the pH. Using the hydration thermodynamic model, nuclear waste glass durability in saturated repository environments can be predicted from the glass composition and the groundwater and the groundwater pH. 47 refs., 3 figs. 1 tab.
There is an extremely voluminous literature on radioactive waste and its disposal, much in the form of government-sponsored research reports. To wade through this mountain of literature is indeed a tedious task, and it is safe to speculate that very few, if any, individuals have the time to examine each report that has been issued during the preceding ten years. This book attempts to summarize much of this literature. Further, many workers in the geosciences have not received training in the nuclear sciences, and many nuclear scientists could be better versed in geology. In this book an attempt is made to cover some background material on radioactive wastes and geotoxicity that may not be an integral part of a geologist's training, and background material on geology and geochemistry for the nuclear scientist. The geochemical material is designed for both the geoscientist and the nuclear scientist. There is no specific level for this book. Certainly, it should be useful to advanced undergraduates and graduates studying geology and nuclear science. It does not pretend to cover a tremendous amount of detail in all subjects, yet the references cited provide the necessary source materials for follow-up study. It is my intention that the reader of this book will have a better, broader understanding of the geochemical aspects of radioactive waste disposal than is otherwise available in anyone source.
