The Effects of Nitric Acid on Extraction Properties of TODGA During Fission Product Management
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The Effects of Nitric Acid on Extraction Properties of TODGA During Fission Product Management Michael A. Bromley and Colin Boxall Engineering Department, Lancaster University, Bailrigg, Lancaster LA1 4YW, UK ABSTRACT In the context of management of the wastes arising from the reprocessing of spent nuclear fuel, studies have been conducted into the solvent extraction kinetics of lanthanide fission products by TODGA and the effects of solvent phase acidity on the effectiveness of this organic extractant molecule. In this study we observe an increase in organic phase viscosity increasing acidity and, potentially by consequence, that the rate of cerium extraction is summarily decreased. INTRODUCTION Nuclear power remains key to energy production strategies worldwide and as such, significant research interest exists within the development of waste management strategies. Several aqueous partitioning processes have been developed to scientific feasibility in recent years (i-SANEX, EXAM, EURO-GANEX) [1] with particular aims to achieve effective recycling of minor actinides from long-lived radioactive waste, thus aiding geological disposal, while future strategies look towards the development of techniques for the dissolution, reprocessing and manufacture of mixed oxide fuels for a safe closed nuclear fuel cycle. Consequently, it is important to develop a comprehensive understanding of the organic complexants and diluents involved in such processes including their long-term suitability and potential for regeneration and recycling in order to minimize process waste and cost. As such, we are conducting ongoing studies into the kinetics of the extraction of lanthanide fission products (as minor actinide simulants) from HNO3 by the trivalent organic extractant molecule TODGA (N,N,N’,N’- tetraoctyl diglycolamide) with the use of a rotating diffusion cell (RDC) [2]. The RDC is a compartmental diffusion apparatus which enables the study of interfacial kinetics and the interrogation of several kinetic regimes from mass transport to thermodynamic control as well as the transition between the two [3]. Through use of this technique, we have quantified the interfacial kinetics of the extraction of Ce(III) by TODGA [4] and have identified that the key complexation reaction takes place in the aqueous solution phase [5]. Further observations have shown the rate of Ce extraction to have linear dependence on the aqueous concentrations of both Ce(III) and HNO3 (not shown), indicating that the extraction process occurs with the inclusion of a single nitrate ion in the first coordination sphere of the Ce(III)-TODGA complex; and, through variation of both hydrodynamic conditions and key solution concentrations, that the system operates under mixed mass transfer with chemical reaction (MTWCR) control [6]. These observations are in agreement with concurrent studies Lelias et al [4] and Simonin et al [4]. We have also observed a reduction in the extraction kinetics of the Ce(III) / TODGA system where the organic solution phase is acidified by HNO3
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