The management and disposal of radioactive wastes are key international issues requiring a sound, fundamental scientific basis to insure public and environmental protection. Large quantities of existing nuclear waste must be treated to encapsulate the radioactivity in a form suitable for disposal. The treatment of this waste, due to its extreme diversity, presents tremendous engineering and scientific challenges. Geologic isolation of transuranic waste is the approach currently proposed by all nuclear countries for its final disposal. To be successful in this endeavor, it is necessary to understand the behavior of plutonium and the other actinides in relevant environmental media. Conceptual models for stored high level waste and waste repository systems present many sCientific difficulties due to their complexity and non-ideality. For example, much of the high level nuclear waste in the US is stored as alkaline concentrated electrolyte materials, where the chemistry of the actinides under such conditions is not well understood. This lack of understanding limits the successful separation and treatment of these wastes. Also, countries such as the US and Germany plan to dispose of actinide bearing wastes in geologic salt deposits. In this case, understanding the speciation and transport properties of actinides in brines is critical for confidence in repository performance and risk assessment activities. Many deep groundwaters underlying existing contaminated sites are also high in ionic strength. Until recently, the scientific basis for describing actinide chemistry in such systems was extremely limited.

Inhalt
Actinide Chemistry In High Ionic Strength Media: General Aspects.- Near Field and Far Field Interactions and Data Needs for Geologic Disposal of Nuclear Waste.- Modern Speciation Techniques Applied to Environmental Systems.- Modeling the Effect of Ionic Interactions on Radionuclides in Natural Waters.- Use of Dissolved and Colloidal Actinide Parameters within the 1996 Waste Isolation Pilot Plant Compliance Certification Application.- Chemical Species of Plutonium in Hanford Site Radioactive Tank Wastes.- Actinide Complexation And Solubility.- Dissociation Constants of Carboxylic Acids at High Ionic Strengths.- Correlation of Equilibrium Constants with Ionic Strength by SIT, Pitzer and Parabolic Models.- Actinyl(VI) Carbonates in Concentrated Sodium Chloride Solutions: Characterization, Solubility, and Stability.- Solubility of NaNd(CO3)2.6H2O(c) in Mixed Electrolyte (Na-Cl-CO3-HCO3) and Synthetic Brine Solutions.- Plutonium (VI) Solubility Studies in Savannah River Site High-Level Waste.- UO22+ and NpO22+ Complexation with Citrate in Brine Solutions.- Complexation and Ion Interactions In Am(III)/EDTA/NaCl Ternary System.- Interaction of Uranyl with Humic and Fulvic Acids at High Ionic Strength.- Actinide Colloidal And Microbiological Interactions.- Retardation of Colloidal Actinides through Filtration in Intrusion Borehole Backfill at the Waste Isolation Pilot Plant (WIPP).- Contribution of Mineral-Fragment Type Pseudo-Colloids to the Mobile Actinide Source Term of the Waste Isolation Pilot Plant (WIPP).- Laboratory Evaluation of Colloidal Actinide Transport at the Waste Isolation Pilot Plant(WIPP): 1. Crushed-Dolomite Column Flow Experiments.- Laboratory Evaluation of Colloid Transport under Simulated Subsurface Conditions at the Waste Isolation Pilot Plant (WIPP): 2.Large-Scale-Intact-Core Column Flow Experiments.- Toxicity of Actinides to Bacterial Strains Isolated from the Waste Isolation Pilot Plant(WIPP) Environment.