RHEOLOGY OF CONCENTRATED, HETEROGENEOUS SLURRIES CONTAINING GREATER-THAN-1M ELECTROLYTE - A CASE-STUDY IN NUCLEAR WASTE SUSPENSIONS

Neutralized current acid waste (NCAW) simulant was produced to chemica lly simulate the properties of the washed solids of a high-level waste stream generated from the reprocessing of irradiated nuclear fuel. Th e NCAW simulant was evaluated by viscosity, yield stress, solid loadin g, particle size, and anion and cation solubility. For similar solid l oadings and pH, the NCAW simulant had higher yield stresses and viscos ities than NCAW. The differences in the rheological behavior between N CAW and the simulant were attributed to differences in the suspension microstructure. The effects of formic and nitric acid additions to the NCAW simulant on yield stress and viscosity were measured as a functi on of solids loading and pH for both acids. In addition, anion and cat ion solubilities were evaluated. Viscosity and yield stress decreased as pH was lowered. The change in rheological properties was attributed to flee breakdown and particle dissolution, which were initiated by t he solubilization of the waste constituents. These results show that t he effectiveness of the simulant studied here is unproven rheologicall y.