Separation of Actinide Elements by Solvent Extraction Using Centrifugal Contactors in the NEXT Process

Abstract

Using the advanced aqueous reprocessing system named NEXT process, actinides recovery was attempted by both a simplified solvent extraction process using TBP as an extractant for U, Pu and Np co-recovery and the SETFICS process for Am and Cm recovery from the raffinate. In U, Pu and Np co-recovery experiments a single cycle flow sheet was used under high nitric acid concentration in the feed solution or scrubbing solution. High nitric acid concentration in the feed solution aided Np oxidation not only in the feed solution, but also at the extraction section. This oxidation reaction accomplished Np extraction by TBP with U and Pu. Most of Np could be recovered into the product solution. In the SETFICS process, a TRUEX solvent of 0.2 mol/dm 3 CMPO and 1.4 mol/dm 3 TBP in n-dodecane was employed instead of 0.2 mol/dm 3 CMPO and 1.0 mol/dm 3 TBP in n-dodecane in order to increase the loading of metals. Instead of sodium nitrate, hydroxylamine nitrate was applied to this experimental flow sheet in accordance with a ''salt-free'' concept. The counter current experiment succeeded with the Am and Cm product. On the high-loading flow sheet, compared with the previous flow sheet, the flow of the aqueous effluents and spent solvent were expected to decrease by about one half. Two solvent extraction experiments for actinides recovery demonstrated the utility of the flow sheet of these processes in the NEXT process.

Influence of nitric acid and plutonium concentrations in dissolver solution of mixed oxide fuel on decontamination factors for uranyl nitrate hexahydrate crystal

“…Uranium, which is the main element in the irradiated fuel, is partially separated as UNH crystals as an ingredient for blanket fuels through crystallization prior to solvent extraction. The U crystallization will reduce the amount of throughput in the solvent extraction process, and as a result will reduce the costs by using small equipment and a reduced the hot cell volume in the following solvent extraction process [3]. Moreover, the U/Pu ratio in the dissolver solution can be adjusted in the crystallization process to a suitable Pu content for core fuel fabrication.…”

“…Although the formation of this precipitate is expected to affect the concentrations of HNO 3 and Pu in the dissolver solution, a limited amount of experimental data has been reported on the process to date. In this study, the U crystallization experiments were carried out at the Chemical Processing Facility (CPF) using a dissolver solution of MOX fuel for the purpose of examining the influence of HNO 3 and Pu concentrations in the dissolver solution on the behavior of Pu and FPs. The structure of the UNH crystals obtained was characterized by X-ray diffraction (XRD), and the thermal properties measured by thermogravimetry (TG) and differential thermal analysis (DTA).…”

Uranium, plutonium and neptunium co-recovery with high nitric acid concentration in extraction section by simplified solvent extraction process

“…Using high HNO 3 concentration scrubbing solution is anticipated to result in lower DF of some FPs for U, Pu and Np product. The DF of major FPs, Zr, Ru, Tc, La and Ce were all over 10 5 in the simplified solvent extraction process using 8 mol/dm 3 HNO 3 scrubbing solution [3]. However, further experimental investigation into the DF of FPs is required.…”

“…By this simplified solvent extraction process, we expected Np to become Np(VI), and be co-extracted with U and Pu. It is, however, difficult to predict the Np behavior in a HNO 3 and TBP medium for the following reasons. Firstly, Np has normally three valences, Np(IV), Np(V) and Np(VI), in a HNO 3 solution.…”

“…partitioning and purification sections [2,3]. By this simplified solvent extraction process, we expected Np to become Np(VI), and be co-extracted with U and Pu.…”