Salt Mineralogy of Hanford High-Level Nuclear Waste Staged for Treatment

Abstract

The Hanford site near Richland Washington, United States, is staging some of its 56 million gallons of high-level waste for treatment. Limited understanding of solids precipitated from the concentrated electrolyte solutions complicates the development of waste treatment options. The implications for the precipitation of these solids are that overlying liquids are saturated in these salts, which may cause unwanted precipitation during downstream processing. This study characterizes the salts in two of these Hanford staged feed tanks (Tanks AP-103 and AP-108) by ion chromatography (for anions), X-ray diffraction, polarized light microscopy, and scanning electron microscopy with energy dispersive X-ray spectroscopy. The results show that Na2CO3·H2O (thermonatrite) was the most prevalent salt in one tank, whereas the double salt Na7F(PO4)2·19H2O (natrophosphate) was the dominant salt in the other. Natrophosphate occurred in both tanks as octahedrons in sizes ranging from 10 μm to a millimeter in diameter. Natroxalate (Na2C2O4) and kogarkoite (NaFSO4) were also common phases observed. Waste processing planners should recognize that these salts may have to be dissolved prior to treatment, and solutions saturated with these salts may complicate downstream processing.

A crucible salt saturation method for determining sulfur solubility in glass melt

“…Sulfur is known as a “problematic” component in low‐activity nuclear waste glasses, and to a lesser extent in high‐level, because it has limited solubility in silicate and borosilicate melts compared to the concentration of sulfur in typical wastes . The LAW, a processed water solution containing soluble salts from the tank waste, consists of Na + (predominant cation), (predominant anion), K + , , , , , F − , Cl − , and other minor constituents including organics . Sulfate is one of the critical constituents that limit waste loading for many LAW glasses .…”

Solubility of Sodium Oxalate in Concentrated Electrolyte Solutions

“…1−3 A similar situation prevails in the storage of alkaline nuclear wastes, where Ox 2− builds up, and Na 2 Ox(s) precipitates, over time, again, due to the degradation of larger organics in such environments. 4,5 Sodium oxalate is also problematic elsewhere in the nuclear industry due to the use of oxalic acid to dissolve certain types of waste (and its subsequent neutralization) 6 and the use of oxalate as a complexing agent or precipitant in the processing of various nuclear fuels. 7 The widespread use of oxalate to remove iron-based scale in pipes and other equipment, because of its ability to bind strongly to both Fe(II) and Fe(III), 8 creates similar management and disposal difficulties.…”

A method to apply Zavitsas' aqueous electrolyte model to multicomponent solutions and its equivalence to Zdanovskii's rule

“…[18][19][20] The present author has used both models for radioactive waste at the Hanford Site in the United States. [21][22][23][24] These models and their cousins generally employ some form of the Debeye-Hṻckel equation in order to model electrolyte solution properties at low concentrations where the Debeye-Hṻckel equation applies. The Debeye-Hṻckel equation becomes increasingly less accurate as the concentration increases above 0.01 molal.…”