Selective Separation of U(VI) from Pu(IV) by 2,9-Diamide-1,10-phenanthroline Ligands at High Acidity: Extraction and Coordination Chemistry

During the PUREX process, the separation between U(VI) and Pu(IV) is achieved by reducing Pu(IV) to Pu(III), which is complicated and energy-consuming. To address this issue, we report here the first case of separation of U(VI) from Pu(IV) by o-phenanthroline diamide ligands under high acidity. Two new o-phenanthroline diamide ligands (1,10-phenanthroline-2,9-diyl)bis(indolin-1-ylmethanone) (L1) and (1,10-phenanthroline-2,9-diyl)bis((2-methylindolin-1-yl)methanone) (L2) were synthesized, which can effectively separate U(VI) from Pu(IV) even at 4 mol/L HNO3. The highest separation factor of U(VI) and Pu(IV) can reach over 1000, setting a new record for the separation of U(VI) from Pu(IV) under high acidity. Furthermore, extracted U(VI) can be easily recovered with water or dilute nitric acid, and the extraction performance remains stable even after 150 kGy gamma irradiation, which provides solid experimental support for potential engineering applications. The results of UV-vis titration and single-crystal X-ray diffraction measurements show that the 1:1 complex formed by L1 with U(VI) is more stable than all of the previously reported phenanthroline ligands, which reasonably reveals that the ligand L1 designed in this work has excellent affinity for U(VI). The findings of this work promise to contribute to the facilitation of the PUREX process by avoiding the use of reducing agents. It also provides new clues for designing ligands to achieve efficient separation between U(VI) and Pu(IV) at high acidity.

Dosimetry and methodology of gamma irradiation for degradation studies on solvent extraction systems

The recycling of minor actinides from dissolved nuclear fuels by hydrometallurgical separation is one challenging strategy for the management of spent fuel. These future separation processes will likely be based on solvent extraction processes in which an organic solvent system (extractant and diluent) will be contacted with highly radioactive aqueous solutions. To establish a separation between different elements in spent nuclear fuel, many extractants have been studied in the past. A particular example is N,N,N′,N′-tetraoctyl diglycolamide (TODGA), which co-extracts lanthanides and actinides from nitric acid solutions into an organic phase (e.g. TODGA in n-dodecane). The radiolytic stability of these extractants is crucial, since they will absorb high doses of ionizing radiation during their usage. Worldwide, different gamma irradiation facilities are employed to expose extractants to ionizing radiation and gain insight in their radiation stability. The facilities differ in many ways, such as their environment (pool-type or dry), configuration and gamma sources (often 60Co or spent nuclear fuel). In this paper, a dosimetric assessment is made using different dosimeter systems in a pool-type irradiation facility, which has the advantage to be flexible in its arrangement of 60Co sources. It is shown that Red Perspex dosimeters can be used to accurately characterize this high dose rate gamma irradiation field (approx. 13.6 kGy h−1), after comparison with alanine, Fricke and ceric-cerous dosimetry in a lower dose rate gamma irradiation field (approx. 0.5 kGy h−1). A final validation of the whole chain of techniques is obtained by reproduction of the dose constants for TODGA in n-dodecane.

Synthesis of soft N-donor isoPentyl-BTBP and study on its removal of actinides from high level liquid waste

To directly separate actinides from high level liquid waste (HLLW), a novel molecule, i. e. isoPentyl-BTBP (6,6′-bis(5,6-bis(4-methylpentyl)-1,2,4-triazin-3-yl)-2,2′-bipyridines) was synthesized and characterized. A kind of isoPentyl-BTBP/SiO2-P adsorbent was obtained by impregnating isoPentyl-BTBP into porous silica/polymer support particles SiO2-P under reduced pressure. The effect of HNO3 concentration, contact time on the adsorption of isoPentyl-BTBP/SiO2-P towards 241Am(III) and 239Pu(IV) was studied. And the stability of isoPentyl-BTBP/SiO2-P in HNO3 medium was also evaluated. It turned out that isoPentyl-BTBP/SiO2-P had much higher affinity for 241Am(III) and 239Pu(IV) over FP elements in 3 M HNO3, fast adsorption kinetics towards 239Pu(IV), excellent stability in HNO3 medium, and should be a very promising adsorbent for separating 239Pu(IV) and 241Am(III) from HLLW.

A first phosphine oxide-based extractant with high Am/Cm selectivity

A new phosphine oxide ligand demonstrates high selectivity for the Am–Cm pair with SF = 2.9–3.5 and the Am–Eu pair with SF = 7.3–8.5 in the range of 0.1–3 M nitric acid.

Radiolysis of alkyl substituted tridentate 2,6-bis(1,2,4-triazine-3-yl)pyridines: an experimental study with DFT validation

The radiolysis products of alkyl substituted tridentate 2,6-bis(1,2,4-triazine-3-yl)pyridines (BTPs) were studied by an experimental study with DFT validation.

Testing a simple approach for theoretical evaluation of radiolysis products in extraction systems. A case of N,O-donor ligands for Am/Eu separation

Here we present experimental confirmation of the theoretical calculation of organic ligands' radiolytic degradation.

Extraction mechanism and γ-radiation effect on the removal of Eu3+ by a novel BTPhen/[Cnmim][NTf2] system in the presence of nitric acid

The extraction mechanism of Eu³⁺ by using BTPhen/[C_nmim][NTf₂] (n = 2, 4, 8) was investigated in the presence of nitric acid, and the new extraction system shows high radiation stability.

Influence of radiation effect on extractability of an isobutyl-BTP/ionic liquid system: quantitative analysis and identification of radiolytic products

Approaches were established for assessing the influence of radiation effect on the extractability of the 2,6-di(5,6-diisobutyl-1,2,4-triazin-3-yl)pyridine (isobutyl-BTP)/1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide ([C₂mim][NTf₂]) extraction system.