Speaker
Description
Division of Nuclear Chemistry and Industrial Materials Recycling, Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 412 96 Gothenburg, Sweden
Closing the nuclear fuel cycle requires separation processes that recover actinides efficiently while minimizing the radiotoxicity and heat load of the waste requiring long-term storage. In this context, advanced reprocessing strategies increasingly target the recycling of minor actinides (MAs: Am, Cm, Np).(1) CHALMEX is an advanced aqueous solvent-extraction concept derived from the second cycle of the GANEX (Grouped ActiNide Extraction) process, with the goal of recovering all actinides in a grouped manner. (2) Accordingly, CHALMEX focuses on one-stage co-extraction of U, Pu and minor actinides from spent nuclear fuel raffinates.
This study compares the traditional extractant tri-n-butyl phosphate (TBP) with the CHON-compliant monoamide, N,N-dibutyl octanamide (DBOA) formulated in the fluorinated diluent FS-13. In both cases, CyMe₄-BTBP was to enable grouped extraction across the different actinide oxidation states relevant to spent nuclear fuel. Batch solvent-extraction experiments were performed using equal volumes of organic and aqueous phases (1.5 mL each). The aqueous feed was an inactive simulated PUREX raffinate prepared in 3 M HNO₃, containing representative fission and corrosion products (lanthanides and transition metals) and spiked with trace concentrations of U(VI), Np(V), Pu(IV), Am(III), and Cm(III). To suppress co-extraction of selected fission products, Bimet and D-mannitol were added as masking agents.
The performance was first investigated in batch tests, together with fission- and corrosion-product behavior and solvent stability under process-relevant aging. Radiolytic stability was assessed by γ-irradiation of the organic phases up to 300 kGy, followed by re-evaluation of extraction performance, which allowed any changes to be correlated with solvent aging and degradation. Under identical conditions, the DBOA-based solvent extracted U(VI) and Pu(IV) efficiently, in line with the expected formation of neutral nitrate adducts such as UO₂(NO₃)₂·2DBOA and Pu(NO₃)₄·2DBOA. Notably, Pu(IV) exhibited a higher distribution into the organic phase compared with the TBP-based system. Based on these batch screening results, actinide recovery was then evaluated in a representative flowsheet sequence comprising extraction, scrubbing with 3.5 M NaNO₃ + 0.5 M HNO₃, and stripping with 0.5 M glycolic acid at pH 4. Overall, the DBOA solvent achieved effective grouped actinide co-extraction and subsequent back-extraction under the selected conditions while retaining acceptable selectivity against fission products.
Reference:
1. OECD Nuclear Energy Agency (NEA). Strategies and Considerations for the Back End of the Fuel Cycle. OECD Publishing (2021).
2. Authen, Thea Lyseid, et al. Solvent Extraction and Ion Exchange 40.3 (2022): 189–202.