Abstract
As the Hanford site undergoes remediation, it is noted that significant economies could be realized by minimizing the amount of aluminum deposited in High-Level Waste glass. Though such a step is not planned, an acidic scrub of the Hanford sludge could enhance Al removal. It is likely that the resulting Al(NO3)3 solution would contain measurable amounts of transuranic elements, thus the solution might require some secondary treatment to remove TRU contamination. Thus far, extraction chromatography (EXC) has shown promise [1] as an alternative to a liquid-liquid remediation of the Hanford site. Previous EXC studies have shown >99% of the Eu can be extracted from simulated Al/Cr waste. This study continues an examination of a hypothetical secondary cleanup of the waste by studying the removal of UO22+, NpO2+, NpO22+ and Th4+ from using tri-n-octyl phospine oxide (TOPO) impregnated XAD7 resins. Neptunium was held in the V and VI oxidation states using ascorbic acid and chromate, respectively. Initial results show extraction following classical metal recovery trends, wherein an increased Zeff correlates with increased distribution of the metal into the organic resin phase. The uptake of Eu3+ (representative of An3+) on a column of the same material was also investigated. Uptake kinetics were improved by wetting the TOPO-XAD7 resin with n-dodecane (TOPO-XAD7n). The presence of n-dodecane also provided consistency between batch mode and column mode metal recovery. Preliminary data show >99% recovery of metal ions with a Zeff ≥ 3 under various simulated conditions.
Highlights
The Hanford Site, in south central Washington state, was the first facility to produce plutonium for nuclear weapons
The dried resin was removed from the oven, allowed to cool in a vacuum desiccator, weighed and contacted for 15 minutes by vigorous shaking with 1 M tri-n-octyl phospine oxide (TOPO) in MeOH using excess TOPO impregnation solution
This ratio would minimize the presence of excess n-dodecane and potential loss of TOPO to the walls of glass vials used during the wetting process
Summary
The Hanford Site, in south central Washington state, was the first facility to produce plutonium for nuclear weapons. Research and remediation efforts have focused on caustic leaching to remove problematic nonradioactive elements, aluminum and chromium. Removal of these species would decrease volume and improve the glass matrix of the vitrified high level waste (HLW). An alternative to SX, extraction chromatography (EXC), provides potential benefits, such as: preconcentration, removal of a liquid organic diluent, the ease of handling of ion-exchange resins and minimized complications arising from third phase formation. The decontamination method investigated examines the efficiency of an EXC approach of TOPO-XAD7 extractant phases to selectively separate radioactive Eu, U, Th and Np from aqueous solutions of HNO3 and Al(NO3) in the presence of low concentrations of Cr
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