Silica-based waste form for immobilization of iodine from reprocessing plant off-gas streams

A high selectivity and sorption capacity for iodine and a feasible consolidation to a durable SiO2-based waste form makes silver-functionalized silica aerogel (Ag-aerogel) an attractive choice for the removal and sequestration of iodine compounds from the off-gas of a nuclear fuel reprocessing plant. Hot uniaxial pressing of iodine-loaded Ag-aerogel (20.2 mass% iodine) at 1200 degrees C for 30 min under 29 MPa pressure provided a partially sintered product with residual open porosity of 16.9% that retained -93% of sorbed iodine. Highly iodine-loaded Ag-aerogel was successfully consolidated by hot isostatic pressing at 1200 degrees C with a 30-min hold and under 207 MPa. The fully densified waste form had a bulk density of 3.3 x 10(3) kg/m(3) and contained -39 mass% iodine. The iodine was retained in the form of nano- and micro-particles of AgI that were uniformly distributed inside and along boundaries of fused silica grains. (C) 2016 Elsevier B.V. All rights reserved.