Radiolytic behaviour of a TODGA based solvent under alpha irradiation
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Radiolytic behaviour of a TODGA based solvent under alpha irradiation R. Malmbeck1 · N. L. Banik1 Received: 14 May 2020 / Accepted: 2 October 2020 / Published online: 29 October 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract In this work the radiolytic stability of a TODGA based solvent has been investigated in alpha radiolysis measured by solvent extraction distribution ratios. Solutions of TODGA in alkane diluents have been subjected to 244Cm α-irradiation in the presence of nitric acid (0.5 M) and analysed using radiometric techniques to determine their rates of radiolytic degradation. It was shown that alpha radiolysis, similarly to external gamma irradiation, produces an exponential decrease of the free TODGA concentration of the organic solvent as the solvent is degraded with increasing absorbed alpha dose. The degradation constant, obtained from the exponential decrease, indicates that the free TODGA concentration is halved with every 1.0 MGy deposited to the solvent from internal alpha decay. This result could be useful information when dealing with high activity actinide solutions in TODGA based solvent extraction systems. Keywords Alpha irradiation · Radiolysis · TODGA · Absorbed dose · Solvent extraction · Cm and Am
Introduction TODGA (N,N,N´,N´-tetraoctyldiglycolamide) (Fig. 1), especially when dissolved in a non- polar diluent and not in contact with a strong acidic system, is hydrolytically stable and has a high selectivity towards trivalent and tetravalent elements [1, 2]. TODGA based extraction systems have been proposed [3, 4] and developed for several nuclear hydrometallurgical partitioning processes [5], focussing mainly on the extraction and recovery of trivalent minor actinides [6, 7]. Recently a TODGA based system was also developed for the grouped actinide extraction process, the so called GANEX process [8–11]. In an extraction process, the solvent becomes highly radioactive when it is contacted with the actinide containing aqueous solution. Radioactive decay of extracted actinides induces damage to the solvent through radiolysis, which generally results in a breakdown of the active extracting molecule and formation of radiolysis products. Radiolysis usually has a negative influence on the performance of the organic solvent as the new species generated very often have * N. L. Banik [email protected] 1
European Commission – Joint Research Centre – JRC, Directorate G, Nuclear Safety and Security, 76125 Karlsruhe, Germany
extracting properties that markedly differ from those of the original ligands. In the case of TODGA, solvent degradation potentially also leads to enhanced risk of phase instability due to third phase formation [5, 12, 13]. The extraction properties of the solvent can only be maintained if the extractant is reasonable resistant to ionising radiation, delivered primarily through alpha decay of the extracted actinide metals. For extraction process development it is therefore a crucial issue to investigate and understand the radiolytic stability of the solve
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