Ionic liquids for separating the minor actinides americium and curium originating from spent nuclear fuel

SCK•CEN Mentor

Zsabka Peter, pzsabka@sckcen.be, +32 (0)14 33 32 14

Expert group

Radiochemistry

SCK•CEN Co-mentor

Cardinaels Thomas , tcardina@sckcen.be , +32 (0)14 33 32 00

Introduction

Without further treatment, spent nuclear fuel has to be securely stored and isolated from the environment for at least 250,000 years to prevent the spread of contamination in the biosphere. By a progressive deployment of GenIV fast reactors, together with the introduction of Pu multi-recycling into the fuel cycle, the confinement time of nuclear waste can be reduced to 10,000 years. Such a timescale is still too long to ensure the reliability of engineered and geological barriers. If we consider the full removal of plutonium (Pu) and uranium (U) from spent fuel, after a few hundreds of years of cooling, the remaining radiotoxicity and heat load of highly active waste is governed by the long-lived minor actinides  americium (Am), curium (Cm) and neptunium (Np).

Np, having multiple stable oxidations states can be separated from spent fuel liquor in a modified PUREX process. The presence of various isotopes of Cm (242Cm - 245Cm) during the fabrication of irradiation targets would require excessive biological shielding (due to neutron emission) and impose rigorous criticality control on the process (due to spontaneous fission). Since the half-life of the most abundant Cm isotopes present in spent fuel is short, it is considered, that an “americium-only” separation from highly active raffinate solution would be the best technical compromise in terms of reduction of waste radiotoxicity, heat load, technical and financial feasibility. Am(III) can be efficiently transmuted into shorter-lived fission products or stable elements via irradiation in a high-flux fast reactor.

In aqueous media Am and Cm, adjacent in the Table of Mendelejev, are only stable in their trivalent oxidation state and show highly similar chemical behaviour. The high chemical similarity between Am(III) and Cm(III) renders their separation challenging.

Objective

The aim of this project is to investigate the solvent extraction performance of ionic-liquid based systems selected for separating the minor actinides Am and Cm , and for the separation of Am(III) only from Ln(III) and Cm(III). The experimental studies shall be using batch solvent extraction (liquid-liquid extraction) methods to investigate the performance and characteristics of the separation system.

During the project, the Master thesis student shall familiarize herself/himself with the relevant literature, alpha and gamma spectroscopy, sample preparation, safe handling of open radioactive sources and the practice of solvent extraction under the supervision of a PhD student.

The minimum diploma level of the candidate needs to be

Academic bachelor , Professional bachelor

The candidate needs to have a background in

Chemistry

Estimated duration

The students is expected to be in Mol for at least 4 months, 6 months would be optimal to complete the full project