Annual Report 2009/2010 - JUWEL - Forschungszentrum Jülich

5.6.
Innovative SANEX process for actinide(III) separation from
PUREX raffinate using TODGA-based solvents
M. Sypula, A. Wilden, C. Schreinemachers, G. Modolo
Corresponding author: g.modolo@fz-juelich.de
Abstract
We studied an innovative SANEX process using N,N,N’,N’-tetraoctyl diglycolamide (TODGA)
based solvents for the selective separation of trivalent actinides from a PUREX raffinate.
TODGA was chosen for actinide(III)/lanthanide(III) co-extraction and 1-octanol was used as
an organic phase modifier to avoid third-phase formation. A new masking agent, trans-1,2-
cyclohexanediaminetetraacetic acid (CDTA) was successfully used for Pd and Zr.
N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) and diethylenetriamine pentaacetic
acid (DTPA) were used as complexing agents for selective actinide(III) stripping. The organic
phase modifier used partly extracted HNO 3 which decreased the pH of the actinide stripping
solution and resulted in a lower Ln(III)/An(III) separation. Therefore several buffers were
studied with the aim of minimising the pH change during An(III) stripping. Good An(III)
stripping conditions were obtained using DTPA + citric acid or DTPA + glycine. All the
established conditions were applied in single centrifugal contactor tests to obtain the data for
future flow-sheet design and spiked counter-current runs using a battery of centrifugal
contactors.
Introduction
The P&T strategy (Partitioning and Transmutation) aims to decrease the radiotoxicity of
nuclear waste and thereby minimise the cost and time associated with its storage. After the
recovery of U, Pu and optionally Np in the PUREX process (Plutonium Uranium Recovery by
EXtraction), the main contributors to the total radiotoxicity of the remaining waste are the
trivalent minor actinides Am+Cm (~0.1% of the total spent fuel mass). Therefore, their
transformation into stable or short-lived isotopes is highly desirable. Prior to the
transmutation, the separation of lanthanides (Ln) is necessary since large neutron-capture
cross-sections would hinder an efficient transmutation. One of the concepts for trivalent
actinide separation being studied in the European ACSEPT project [1] is the innovative
SANEX concept (Selective ActiNide EXtraction). It consists of an An(III)/Ln(III) co-extraction
step, followed by selective An(III) stripping using hydrophilic complexing agents. In the final
step, lanthanides are stripped to the aqueous phase using diluted nitric acid. The most
challenging part of this process is the selective An(III) stripping, where the pH value of the
stripping solution and the choice of an appropriate hydrophilic An(III) complexing agent are
crucial.
Methodology
Batch extraction experiments were performed in 2 mL glass vials. 500 μL of organic and
aqueous phases were spiked with 10 μL of radiotracer ( 241 Am, 152 Eu, approx. 25 kBq/mL) and
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