Rheology of concentrated, heterogeneous slurries containing > 1M electrolyte — a case study in nuclear waste suspensions

Abstract

Neutralized current acid waste (NCAW) simulant was produced to chemically simulate the properties of the washed solids of a high-level waste stream generated from the reprocessing of irradiated nuclear fuel. The NCAW simulant was evaluated by viscosity, yield stress, solid loading, particle size, and anion and cation solubility. For similar solid loadings and pH, the NCAW stimulant had higher yield stresses and viscosities than NCAW. The differences in the rheological behavior between NCAW 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 function of solids loading and pH for both acids. In addition, anion and cation solubilities were evaluated. Viscosity and yield stress decreased as pH was lowered. The change in theological properties was attributed to floc breakdown and particle dissolution, which were initiated by the solubilization of the waste constituents. These results show that the effectiveness of the simulant studied here is unproven rheologically.