(120b) Structural Characterisation, Growth Kinetics and Sedimentation Dynamics of Polymer-Mg/Al Hydroxide Flocculant Systems in the Nuclear Industry

Hazzard and risk reduction and legacy material (fuel and sludge) retrieval is paramount when considering the UK nuclear decommissioning strategy; with first generation facilities being of priority due their advanced age and fatigue. Over half a decade, the first generation fuel rod cladding material has severely degraded in open air wet storage to produce stable colloidal/slow settling material consisting of magnesium-aluminium hydroxides, silicates and carbonates with uranyl complexes associated with many of these aggregates. These particle systems drastically decrease visibility in wet storage facilities making fuel and sludge retrieval near impossible and little aggravation of the settled solids is required for resuspension to occur halting operations. In addition, these suspended complexes reduce decontamination factors in downstream facilities, most notably, ion exchange operations before discharge to sea.

Polymer driven flocculation has been a method applied by industries including composite materials synthesis, paper manufacturing, and water treatment. The colloidal complexes in these wet storage facilities are known to be polydisperse pseudo-hexagonal platelets and particle-polymer floc structure assembly dynamics is non trivial. The role of polymer conformation time to particle surfaces has been discussed in great amounts of literature and is considered consensus in determining the structure of these macro-aggregate polymer-particulate systems.

Magnesium and aluminium hydroxide bulk density was analysed using hindered settling test correlations to determine the sedimentation dynamics of these materials without addition of settling aids. The surface properties of these materials including morphology, surface charge and area were investigated using Scanning Electron Microscopy (SEM), Electrophoresis and BET isotherm techniques respectively. The self-coagulation dynamics and structure of these particles was also investigated using sonification coupled with Static Light Scattering (SLS) to achieve a Particle Size Distribution (PSD) and 3-dimensionsional fractal dimension of these self-coagulating aggregates.

The effect of polyacrylamide-polyacrylic acid co-polymers on the flocculation dynamics was investigated regarding the particle-polymer floc growth kinetics in varying shear conditions using Focused Beam Reflectance Measurement (FBRM). The influence of polymer to particle ratio and polymer charge density on the structure was acquired via 3-dimensional fractal dimensions using SLS and a PSD was obtained using a combination of SLS and FBRM. Characterisation of the floc configuration preference to bridging or electrostatic patch regimes were qualitatively determined using a flowing microscope instrument (FLOCAM). Overall impact on these resultant flocs structures on their sedimentation dynamics was compared through traditional settling tests and optimum dose and polymer charge density for such systems was determined.