Modeling and flowsheet design of an Am separation process using TODGA and TPAEN
Résumé
Recycling americium from spent fuels is an important option considered for the future nuclear cycle as americium is the main contributor to the long-term radiotoxicity and heat power of the ultimate waste. The separation of americium alone from a PUREX raffinate can be achieved by co-extracting lanthanide (Ln) and actinide (III) cations in an organic phase containing TODGA diglycolamide extractant (N,N,N',N'-tetraoctyldiglycoamide), and then strip Am(III) with selectivity towards curium and lanthanides (by analogy with the i-SANEX process for example). The water soluble ligand TPAEN (N,N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]-ethylenediamine) was tested to selectively strip Am from a loaded organic phase. Based on experimental data obtained by the Julich and the CEA teams since 2013, a phenomenological model has been developed to simulate the behavior of americium, curium and lanthanides towards their extraction by TODGA and their complexation by TPAEN (complex stoichiometry, extraction and complexation constants, kinetics). The model was gradually implemented in the PAREX code and help at finding the best operating conditions. Thus, the following modifications were proposed An increase in the concentration of TPAEN as much as allowed by the solubility limit.An improvement of the lanthanide scrubbing from the americium flow by adding nitrates in the aqueous phase.A qualification of the model was begun by comparing on one hand constants determined with the model to those measured experimentally and on the other hand simulation results and experimental data on new independent batch experiments.A first sensitivity analysis identified which parameter has the most preponderant effect on the process. A flowsheet was proposed for a spiked test in centrifugal contactors performing with a simulated PUREX raffinate with traces amounts of Am and Cm. If the feasibility of the process is confirmed, the results of this test will be used to consolidate the model and to design a flowsheet for a test on a genuine PUREX raffinate.This work is the result of collaborations in the framework of the SACSESS European Project.