PNNL

Abstract

To prevent the release of radioiodine during the reprocessing of used nuclear fuel or in the management of other radioactive wastes many technologies have been developed for the capture of iodine. The capture is only one portion of the challenge as a durable waste form is required to ensure safe disposal of the long lived radioiodine. This work presents the first durability studies in dilute, flow-through conditions of two AgI-containing waste forms: hot-isostatically pressed silver mordenite (AgZ) and spark plasma sintered silica functionalized silica aerogel (SFA) iodine waste forms (IWF). Using the single pass flow through (SPFT) test method the dissolution rates respective to Si, Al, Ag and I were measured for variants of the two IWF types. Combining solution and solids analysis information on the mechanism of corrosion in neutral to alkaline conditions. The AgZ samples were observed to have corrosion attack preferentially occur at secondary phases with higher Al and alkali content. These phases contain a lower proportion of the I compared with the matrix. The SFA samples experienced a higher extent of corrosion at Si-rich particles, but an increased addition of Si to the waste lead to an improvement in overall corrosion resistance. The dissolution rates for the two IWF types are of similar magnitude to other Si-based waste form materials measured in SPFT testing.