Plutonium (VI) Solubility Studies in Savannah River Site High-Level Waste
The high-level waste tanks at Savannah River and Hanford contain a layer of insoluble solids (“sludge”) and a supernatant liquid; the latter a strongly basic solution of sodium nitrate, nitrite, and aluminate at mole/L levels and sodium carbonate, sulfate, chloride, etc. at 0.1 M to 10−2 M or less. Plutonium is present at a 103 to 106 α d/min-mL level; the radiation level of the solution is about 4 × 104 R/hr from 137Cs γ-rays. To conserve space in the waste tanks, the supernate is evaporated to a specific gravity of 1.35–1.40 and returned to the waste tank, where the least soluble salts crystallize. This process is repeated as necessary. The most soluble species (sodium hydroxide, nitrite, aluminate, chloride) increase in concentration during evaporation and other species (sodium carbonate, sulfate, phosphate) are precipitated with sodium nitrate.
KeywordsHydroxide Sludge Geochemistry Nitrite Plutonium
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