Neptunium Disposal to the Savannah River Site Tank Farm

Abstract:

Researchers investigated the neutralization of an acidic neptunium solution from a Savannah River Site (SRS) processing canyon and the properties of the resulting slurry to determine the feasibility of disposal in the SRS tank farm. The acidic solution displayed no properties that precluded the proposed disposal route. Neutralization of the acidic neptunium forms a 4wt% slurry of precipitated metal hydroxides. The insoluble solids consist largely of iron (92%) and neptunium hydroxides (2%). The concentration of soluble neptunium remaining after neutralization equaled 1.8 + 0.6mg/L, much less than previous solubility measurements predicted. Researchers used an apparatus similar to an Ostwald-type viscometer to estimate the consistency of the neptunium slurry with the solids present. The yield stress and consistency of the 4 wt% slurry will allow transfer through the tank farm, although concentration of the insoluble solids above 4wt% may cause significant problems due to increased consistency and yield stress. The consistency of the 4wt% slurry is 7.6 centipoise (cP) with a yield stress less than 1 Pascal (Pa). The neptunium slurry, when combined with actual washed radioactive sludge, slightly reduces the yield stress and consistency of the sludge and produces a combined slurry with acceptable rheological properties for vitrification in the Defense Waste Processing Facility (DWPF).