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The reprocessing of spent nuclear fuel is currently moving towards advanced cycles that contemplate the recycling of minor actinides, in particular americium (Am), as a strategy to minimise the radiotoxicity of the waste that must be stored [1]. Most of the recycling strategies developed to achieve an advanced closed cycle use the PUREX raffinate as a starting point. In this context, the separation of Am from the rest of the actinides, particularly from curium (Cm), has gained interest. Accordingly, the AmSel (Americium Selective) extraction process [2], which consists of three steps, has emerged. In particular, for the recovery of Am, the organic extractant TODGA and the aqueous ligand SO3-Ph-BTBP are used.
For the development of any extraction process, one of the main safety constraints is the resistance of the solvent to the highly radioactive environment and acidic conditions under which it must operate. Therefore, resistance studies of extraction systems are essential to assess the stability of the ligands and to identify their degradation compounds (DCs). From the perspective of long-term process operation in a future reprocessing plant, it is particularly important to understand the impact that these DCs may have on the extraction performance. Regarding TODGA stability, several authors have investigated its degradation and identified its corresponding DCs [3–4]. In fact, in one of our previous studies, the implications of these DCs on Am/Cm separation during the stripping step of the AmSel process were evaluated, leading to the conclusion that three of them could significantly affect the separation [5]. However, there is still a lack of information on their impact on the entire extraction process, considering all process steps and realistic operating conditions. This work aims to address this gap.
To this end, an organic solvent composed of TODGA was irradiated over several cycles up to moderate absorbed doses at the Náyade facility at CIEMAT using gamma 60Co sources. After each irradiation cycle, the composition of the TODGA solvent was analysed by HPLC–MS, quantifying the TODGA concentration and most of its DCs. To simulate the long-term operation of the process, after each irradiation cycle the remaining TODGA concentration was adjusted to its nominal value and the solvent was subsequently subjected to the next irradiation cycle. Finally, the impact of the degraded TODGA solvent, and consequently the presence of different DCs, was assessed in all steps of the AmSel process. This evaluation was carried out using highly active PUREX raffinate containing fission products and lanthanides, as well as actinide-spiked active solutions. Analyses were performed by gamma spectrometry, alpha spectrometry, and ICP-MS.
[1] Geist, Andreas, et al. Separation science and technology 56.11 (2021): 1866-1881.
[2] Wagner, Christoph, et al. Solvent Extraction and Ion Exchange 34.2 (2016): 103-113.
[3] Sugo, Yumi, Yuji Sasaki, and Shoichi Tachimori. Radiochimica Acta 90.3 (2002): 161-165.
[4] Sánchez-García, Iván, et al. EPJ Nuclear Sciences & Technologies 5 (2019): 19.
[5] Vacas-Arquero, Pablo, et al. Progress in Nuclear Energy 183 (2025): 105677.