Aluminosilicates for the Capture and Immobilization of High-Halide Wastes from Used Nuclear Fuel Reprocessing

摘要

Aluminosilicates were investigated as hosts for capturing and immobilizing halides released during the reprocessing of used nuclear fuels. While some of these concepts would work for capturing and immobilizing halide wastes released during aqueous reprocessing, this work is more focused on pyroprocessing. The primary focuses in the work are 1) using glass-bonded aluminosilicate-based sodalite minerals to immobilize the Cl and I from the pyroprocessing wastes and the glass matrix to immobilize the other fission products released from the fuels and 2) using Ag-loaded aluminosilicate aerogels to capture and immobilize I2(g) released from the fuel at the head-end process where the fuel is first processed and from the actinide or lanthanide drawdown off-gas.;For 1), different approaches were used to make glass-bonded sodalite with various salt wastes including solution-based, hydrothermal, and salt occlusion methods. The primary salts of interest were LiCl-KCl salt wastes (called the "ER" salt) and LiCl-Li2O salt wastes (called the oxide reduction or "OR" salt). Sodalite is a mineral that can be comprised of alkali halides that reside within the beta-cages and have the general formula of Na8(AlSiO4)6Cl2 and Na8(AlSiO4)6I2 for chlorosodalite and iodosodalite, respectively.;For 2), a variety of techniques were used to fabricate Na-Al-Si-O and Al-Si-O aerogels by adjusting several processing variables including alkoxide precursors, catalysts, precursor concentrations, hydrolysis rates (controlling water additions), alcohol dilutions, and atmosphere. Following basic characterizations such as specific surface area and pore volume assessments, the aerogels were subjected to a range of tests including Ag+-impregnation, Ag 0-functionalization (Ag+ was reduced to Ag0 under a flow of H2/Ar), thiolation, and I2(g) capacity. The aerogel products made and processed under these different conditions were compared and contrasted. The iodine loading was upwards of 36 mass% through the chemisorption to form AgI crystals within the aerogel matrix.;In addition to this experimental work, background is provided for pyroprocessing, sodalite formation, and materials for the capture and immobilization of iodine. Where appropriate in each chapter, distinctions are made about which salts or species are of interest.