Combined electron microscopy and vibrational spectroscopy study of corroded Magnox sludge from a legacy spent nuclear fuel storage pond

Characterization of Multiple Hindered Settling Regimes in Aggregated Mineral Suspensions

“…In the SEM image, these platelets are clustered into a small primary agglomerate of around 3 µm in diameter. These agglomerates of hexagonal platelet crystals are consistent with similar images in Gregson et al 34 and Li et al 47 . are sometimes referred to as macro-aggregates and there is evidence in the literature 20,21 that these particles contain higher ratios of intra-aggregate fluid than smaller aggregates.…”

“…The resulting volume weighted median chord length, l 50 , was found to be 152.4 µm, similar to the largest aggregate pictured in Figure 1c and providing further evidence of the formation of macro-aggregates during suspension preparation. Particle phase Scale Evidence Hexagonal platelet crystals <400 nm face width <50 nm thickness SEM images in Figure 1a and Gregson et al 34 , Li et al The gel point, φ g , and final bed concentrations at the end of the batch settling tests, φ F , can be estimated on the basis that magnesium hydroxide is conserved below the settling interface, and hence no small solids remain suspended in the clarified zone. Using this assumption, the product of the instantaneous bulk concentration below the interface,φ(t), and the volume of suspension below the interface, V (t), provides the constant total volume of solids (φ(t)V (t) = constant).…”

“…However, magnesium hydroxide is also the primary corrosion product from Generation I spent nuclear fuel in the UK 34 which was clad with a magnox alloy of magnesium and small amounts of aluminium. Substantial volumes of Mg(OH) 2 rich intermediate level radioactive waste, called corroded magnox sludge (CMS), have accumulated in legacy ponds at the Sellafield nuclear decommissioning site in Cumbria, UK 35,36 .…”

Americium and plutonium association with magnesium hydroxide colloids in alkaline nuclear industry process environments

“…This behaviour has been observed previously. For example, Gregson et al [1,7] also reported a reduction in pH to 8.5e10. This may be attributed to the dissolution of carbon dioxide into the liquor during both sampling (air-lift method) and subsequent handling of the sample in the open atmosphere at the plant during bulking and analysis.…”

“…In the plant, the radionuclide contaminants are removed by passing the solution through sand bed filters, followed by a carbonation step that reduces the pH from approximately 11 to neutral. The carbonated solution then passes through ion-exchange clinoptilolite (zeolite) beds, which are selected to remove 137 Cs and 90 Sr. Gregson et al [1,7] studied the chemical form of sludges and suspended particles and colloids from an alkaline storage pond at Sellafield. They found that the morphology of the magnesium-containing phases was consistent with brucite, but perhaps with some incorporation of Al to form hydrotalcite-like phases.…”