Abstract
To prevent the release of radioiodine during the reprocessing of used nuclear fuel or in the management of other wastes, many technologies have been developed for iodine capture. The capture is only part of the challenge as a durable waste form is required to ensure safe disposal of the radioiodine. This work presents the first durability studies in dilute conditions of two AgI-containing waste forms: hot-isostatically pressed silver mordenite (AgZ) and spark plasma sintered silver-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 IWFs. By combining solution and solid analysis information on the corrosion mechanism neutral-to-alkaline conditions was elucidated. The AgZ samples were observed to have corrosion preferentially occur at secondary phases with higher Al and alkali content. These phases contained a lower proportion of 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 led to an improvement in corrosion resistance. The dissolution rates for the IWF types are of similar magnitude to other Si-based waste form materials measured using SPFT.
Highlights
In the reprocessing of used nuclear fuel, radioiodine will be released, primarily during the dissolution of the fuel [1]
The initial microstructures of the AgZ samples prior to corrosion were observed with scanning electron microscopy (SEM)
No iodine was present in AgZ 1-3 (Figure 2c)
Summary
In the reprocessing of used nuclear fuel, radioiodine will be released, primarily during the dissolution of the fuel [1]. A portion of this iodine is 129 I with a half-life of 15.7 million years; to prevent discharge of this long-lived radionuclide, the released iodine needs to be captured in the off-gas management system of the reprocessing facility. Solid sorbent capture including resins [4], carbon-based materials [5,6,7], metal organic frameworks [8,9], zeolites [10,11,12], silica [13] and aerogels [14,15,16]. One of the primary advantages of solid sorbents is their potential to be readily transformed into a final waste form, through either direct post-processing in a canister or densification. The presence of silver (Ag) in solid sorbents can enhance iodine capture through the generation of silver iodide (AgI) in the material. The stability of AgI can be impacted by its local environment, as its dissolution can be highly affected by redox conditions [18], Materials 2019, 12, 686; doi:10.3390/ma12050686 www.mdpi.com/journal/materials
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