Recovery of Oxidized Actinides, Np(VI), Pu(VI), and Am(VI), from Cocrystallized Uranyl Nitrate Hexahydrate: A Single Technology Approach to Used Nuclear Fuel Recycling

Abstract

The utility of recovering cocrystallized Np, Pu, and Am from a uranyl nitrate hexahydrate crystalline phase has been examined. Progressive dissolution studies were carried out on samples of either Np­(VI), Pu­(VI), or Am­(VI) cocrystallized with uranyl nitrate hexahydrate, resulting in a linear relationship between the amount of actinides dissolved as a function of volume of HNO3 added, which indicates homogeneous distribution of the transuranic species throughout the crystalline solid. The ratio of the concentration of U to the heavier actinides was maintained over the entire dissolution and mimicked that of the starting cocrystallization solution. A series of five crystallization–dissolution–recrystallization cycles of uranyl nitrate hexahydrate from nitric acid have been achieved in the presence of Am­(VI), where the behavior of Am­(VI) followed that of U­(VI) for each step of all five cycles. Negligible reduction of Am­(VI) to Am­(III) was observed between each recrystallization cycle. These results indicate the utility of a group hexavalent actinide cocrystallization approach toward used nuclear fuel recycling.

Ion sieving in graphene oxide membrane enables efficient actinides/lanthanides separation

“…The foregoing results clearly highlight the effectiveness of the ion-sieving strategy for group actinides/lanthanides separation in this work. Notably, the overall An/Ln separation factors in this work are mostly higher than the single-stage separation factors of An/Ln group separation using the extraction method 9 , 39 , 40 and are much higher than those using the crystallization or precipitation method 12 , 13 , 41 .

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“…The foregoing results clearly highlight the effectiveness of the ion-sieving strategy for group actinides/lanthanides separation in this work. Notably, the overall An/Ln separation factors in this work are mostly higher than the single-stage separation factors of An/Ln group separation using the extraction method 9,39,40 and are much higher than those using the crystallization or precipitation method 12,13,41 . Furthermore, in the presence of both TODGA extraction and NaBiO 3 oxidation, the ion sieving results in GOM display permeation trends of Ce > Gd > Eu > Nd for the lanthanides and Am > Pu > Np ~U for the actinides (Figs.…”

“…3e, f prove the efficient ion sieving of U and Np from the lanthanides by the GOM, the other two actinides Pu and Am largely penetrate together with the lanthanides into the RC, emphasizing the necessity of oxidation in the FC to separate Pu and Am from the lanthanides. To address this issue, sodium bismuthate (NaBiO 3 ), known as a highly oxidizing agent capable of oxidizing Am(III) to Am(VI) quantitatively in nitric acid solutions, was employed as the chemical oxidant in this work to oxidize the actinides 12 , 13 , 17 , 36 . Absorption spectra (Supplementary Fig.…”

“…Despite significant progress has been made in the development of the EURO-GANEX process, demerits such as the involvement of a large number of extraction/scrubbing/stripping stages in tandem and the necessity to meticulously control the chemical conditions of both the organic and aqueous solutions may hamper its industrial application. An alternative approach to realize the group separation is to oxidize the actinides together into their high valent oxidation states and then separate them from the lanthanides 7 , 12 , 13 . Apart from the intrinsically stable U(VI), transnuranic elements Np, Pu, and Am can also be oxidized to the +V or +VI oxidation states and exist as linear actinyl ions ([O = An V = O] + or [O = An VI = O] 2+ ) under strong oxidizing conditions.…”

Group Separation of Hexavalent Actinides from Lanthanides through Selective Extraction by Sterically Hindered 2-Ethylhexyl Phosphonic Acid Mono-2-ethylhexyl Ester

“…Recently, a so-called group actinide extraction (GANEX) concept has been proposed to recover all the actinides simultaneously from highly acidic spent fuel solution in a single-step separation, aiming toward the homogeneous recycling of plutonium and minor actinides in a future closed fuel cycle. − However, implementation of such a single-step separation concept is not easy due to the great chemical complexity of the actinides and the presence of a large amount of various fission products. − In particular, the presence of lanthanides is problematic because these 4f-elements exhibit great chemical similarity to the trivalent actinide Am, thus impeding the implementation of group separation strategy for all the actinides. − To overcome this obstacle, significant effort has been devoted into exploiting the different redox chemistries between actinides and lanthanides. ,− The actinides from U to Am can all exist in the hexavalent oxidation state as dioxo-actinyl ions under highly oxidizing conditions, while lanthanides are mainly restrained in the trivalent oxidation state . Consequently, it is possible to achieve a group separation of hexavalent actinides (U to Am) from lanthanides by taking the advantage of the distinct chemical property between the two groups of f-elements ions in terms of both the charge density and steric configuration.…”