Chemical separation and recycling of uranium and plutonium (major actinides) from spent nuclear fuel (SNF) is a mature technology applied on an industrial scale in the well-known PUREX process. The highly active raffinate (HAR) of the PUREX process contains the minor actinides americium (Am) and curium (Cm) and the fission products, including among others the lanthanides (Ln). The various isotopes of Am are responsible for the long-term heat loading of the final waste repository, unless they are separated and managed independently from the HAR. In this way, the safety and footprint (and associated cost) of the final waste repository can be largely reduced. In the frame of continuous EU projects like ACSEPT, SACSESS and the current GENIORS project, several partitioning processes were developed to separate the minor actinides from the PUREX-HAR. The removal of Am and Cm from the PUREX-HAR is envisaged in the so-called DIAMide Extraction (DIAMEX) process, whereby the Ln are co-extracted with Am and Cm. The DIAMEX process is followed by a Selective ActiNide Extraction (SANEX) process to separate Am and Cm from the Ln.
The prevalent current scientific opinion is that the co-management of Am and Cm in the case of a transmutation scenario complicates the target fabrication due to the very high neutron emission by the Cm isotopes that would be separated from the spent fuel. In addition, Cm isotopes cause problems to control the criticality of a fast nuclear reactor. In fact, leaving Cm with the rest of the fission products to the vitrified final waste would not have a significant impact on the long-term radiotoxicity and heat loading and consequently on the footprint of the final repository.
Currently there exists no robust Am/Cm separation process that can be implemented on an industrial scale. Formerly proposed systems suffer from radiolytic degradation of the ligands, low Am/Cm separation factors, production of excessive amount of radioactive process waste or difficulties with the reliable synthesis of the ligands used.
The aim of the PhD project is to develop a continuous process to separate americium from curium and the lanthanides. The project will start from the ionic liquid-based systems developed in a current PhD project. The main focus will be on the use of diluents and/or phase modifiers to facilitate the upscaling and make the system compatible with continuous processes. The effect of diluents and/or phase modifiers on the separation system, and more specifically on the Am/Cm separation, will be thoroughly investigated. In addition, the impact of these diluents and/or phase modifiers on the radiation resistance will be assessed.
To achieve the abovementioned objectives, the PhD candidate will work with radioactive solutions, first on a tracer level, and later on micro-amounts. The project foresees the daily application of batch liquid-liquid extractions, which serve as a tool to assess the viability of a certain system. The parameters to be studied cover a.o. i) modifications of the organic solvent composition by the addition of diluents and/or phase modifiers; ii) modification of the extractants; iii) modification of aqueous feed compositions such as concentration and acidity. Alpha and gamma spectroscopy as well as ICP-MS will be used for the determination of distribution ratios from which the separation factors can be derived. Viable systems will be tested in a continuous counter-current process configuration using centrifugal contactors. Continuous solvent extractions will be performed in campaigns after a thorough experimental design. All required equipment is implemented in the Radiochemistry group.
This project makes a real contribution to optimize the management of Belgium’s spent nuclear fuel by developing innovative separation processes to separate the minor actinides from the final waste fraction.