Homogenous recycling of transuranium elements from irradiated fast reactor fuel by the EURO-GANEX solvent extraction process

The EURO-GANEX process was developed forco-separating transuranium elements from irradiatednuclear fuels. A hot flow-sheet trial was performed in acounter-current centrifugal contactor setup, using a genuinehigh active feed solution. Irradiated mixed (carbide,nitride) U80Pu20 fast reactor fuel containing 20 % Pu wasthermally treated to oxidise it to the oxide form which wasthen dissolved in HNO3. From this solution uranium wasseparated to >99.9 % in a primary solvent extraction cycleusing 1.0 mol/L DEHiBA (N,N-di(2-ethylhexyl)isobutyramidein TPH (hydrogenated tetrapropene) as the organicphase. The raffinate solution from this process, containing10 g/L Pu, was further processed in a second cycle of solventextraction. In this EURO-GANEX flow-sheet, TRU andfission product lanthanides were firstly co-extracted intoa solvent composed of 0.2 mol/L TODGA (N,N,N′,N′-tetran-octyl diglycolamide) and 0.5 mol/L DMDOHEMA (N,N′-dimethyl-N,N′-dioctyl-2-(2-hexyloxy-ethyl) malonamide)dissolved in Exxsol D80, separating them from most otherfission and corrosion products. Subsequently, the TRUwere selectively stripped from the collected loaded solventusing a solution containing 0.055 mol/L SO3-Ph-BTP(2,6-bis(5,6-di(3-sulphophenyl)-1,2,4-triazin-3-yl)pyridinetetrasodium salt) and 1 mol/L AHA (acetohydroxamicacid) in 0.5 mol/L HNO3; lanthanides were finally strippedusing 0.01 mol/L HNO3. Approximately 99.9 % of the TRUand less than 0.1 % of the lanthanides were found in theproduct solution, which also contained the major fractionsof Zr and Mo

Separation of the minor actinides: the DIAMEX-SANEX concept

International audienceThis paper deals with the recent advances concerning the development of the DIAMEX and SANEX processes for the separation of minor actinides (americium and curium) from the raffinates produced by the PUREX process. The DIAMEX process is at the more advanced stage of development with a reference molecule and reference flowsheet well validated through numerous pilot tests. Concerning the SANEX process, the scientific feasibility of two of the three explored routes is now established and the last one is planned to be demonstrated in 2001 summer. So, by the end of 2001, the CEA will be able to select the best route for the demonstration of the minor actinides separation technological feasibility before 2006

DIAMEX-SANEX process development studies

International audienceThis paper describes the way adopted to develop DIAMEX-SANEX process. The organic phase contains two extractants : DMDOHEMA extracting actinides(III) from a high nitric acid medium, and the a cationic exchanger for the extraction at lower acidity. Two concepts are studied : in the first one, extractants mixture is used in the whole process, whereas the second route includes a extractant separation step. In that case, only DMDOHEMA is exposed to high-level raffinate and Mo, Zr extraction could be inhibited. In that case, di-alkyl phosphoric acids with 6 carbon atom on branched chains were the more convenient for actinides and extractant separations. They are lipophilic towards aqueous solutions with pH lower than 4, in order to maintained lanthanides in organic phase. They are moreover soluble in basic aqueous solution, so we could recover a organic phase with only DMDOHEMA and TPH. The route without extractant separation used the well known di-(2-ethyl hexyl) phosphoric acid. The main difficulty in that case, is the management of fission products as molybdenum and zirconium, in order to prevent their stripping with actinides(III) and to back extract them before organic phase recycling. The main goal of theses studies is to carry out experiments useful to elaborate a flowsheet for a genuine hot test on a long duration in 2004

Apport de la simulation à la conduite d'un procédé de séparation d'éléments proches chimiquement

International audienceLa récupération et la purification de métaux dans des minerais ou des matières recyclables nécessitent dans certains cas le développement de systèmes chimiques d'un haut degré de spécialisation jouant sur des différences ténues de comportement entre les éléments. Ces procédés s'avèrent donc très sensibles aux variations de paramètres opératoires et la réussite de leur mise en oeuvre dans des appareils d'extraction liquide-liquide devient très délicate. La modélisation des phénomènes physico-chimiques mis en jeu et leur simulation dans un code de calcul dédié permet de mieux maîtriser et d'anticiper le comportement du système au cours d'un essai. C'est la démarche suivie par Commissariat aux énergies atomiques et aux énergies alternatives (CEA) pour développer des procédés d'extraction liquide-liquide afin de limiter le nombre d'expériences à réaliser tant au niveau du tube en laboratoire que dans une succession d'appareillages d'extraction liquide-liquide. Dans le cadre du recyclage des actinides du combustible nucléaire irradié, le CEA envisage de récupérer l'américium, pour réduire l'emprise thermique au stockage et afin de le transmuter dans des réacteurs de génération IV. Le procédé par extraction liquide-liquide, EXAm, permet cette récupération sélective, s'avérant délicate du fait du comportement de l'américium très proche de celui d'autres éléments comme notamment le curium ou les lanthanides. Cet article montre la démarche du CEA pour développer EXAm en limitant le nombre d'essais à mettre en oeuvre, tout en atteignant les performances requises malgré la très forte sensibilité du système aux variations de certains paramètres opératoires. La démarche s'appuie sur la modélisation des phénomènes prépondérants en adéquation avec les acquisitions expérimentales, données d'extraction ou de spéciation. Pour la seule première étape du procédé EXAm où l'américium est séparé du curium, le modèle global prend en compte soixante-deux équilibres avec leurs constantes thermodynamiques associées. Ce modèle a été introduit dans le code de simulation de procédé nommé PAREX développé au CEA et cofinancé par AREVA-NC. Ce code permet de calculer, en régime stationnaire ou transitoire, les profils de concentrations des éléments modélisés, dans chaque étage du procédé (mélangeur-décanteur ou extracteur centrifuge dans le cas présent). Grâce à sa rapidité de calcul, des études de sensibilité ont été réalisées en faisant varier un grand nombre de paramètres opératoires. Ceux les plus pertinents pour piloter le procédé ont alors été choisis, et des procédures de mise en oeuvre ont pu être définies en amont puis appliquées lors d'un essai en micro-pilote, en se basant sur les analyses en ligne ou déportées, disponibles sur l'installation. L'ajustement en cours d'essai du débit permettant d'injecter le réactif complexant s'est révélé particulièrement efficace pour atteindre des performances très satisfaisantes de récupération de l'américium malgré la difficulté de séparation intrinsèque de cet élément dans le milieu considéré

The PAREX Code: A powerful tool to model and simulate solvent extraction operations

International audienceThe PAREX code has been developed since the nineties by CEA and AREVA to describe the PUREXprocess implemented in the French fuel reprocessing plants. It enables the calculation, either insteady or transitory states, of the behaviour of the different elements of interest at each processstep. The highly customised structure of the software allowed the implementation of variousphenomenological models describing solvent extraction systems dedicated to uranium purificationfrom crude ore to spent fuel. After qualification of the implemented models, the code was used todesign flow sheets for safety demonstration analysis or for operational assistance. CEA is currentlydeveloping a new simulation platform to make the code PAREX perennial and associate it withtools included in a standardised computing background for their perpetuation and sharing ofgeneric functionality. In particular, it is planned to develop validated databases to reference thescientific knowledge useful in modelling development. The platform will adapt the standardphenomenological complexity needed to simulate a reprocessing plant, real or virtual, share toolsand improve the transposition from laboratory scale to industrial scale, thus decreasing thenumber of experimental studies required for the implementation of a process

Modelling and simulation of molybdenum extraction by HDEHP ion-exchanger and DMDOHEMA solvating extractant

International audienceMolybdenum is an element which is co-extracted with other lanthanides or actinides by many organic solvents in liquid-liquid separation processes. Thus, it is often necessary to manage this element to prevent any pollution of the process output. This paper describes the studies carried out by CEA - DRCP to model and better understand the behavior of molybdenum in the EXAm process. The originality of this liquid-liquid extraction process is the simultaneous presence of two extractants in the organic phase, following two types of mechanisms: extraction by solvation thanks to DMDOHEMA or HDEHP, extraction by ion exchange with HDEHP. Although these two extractants play a specific role for the extraction of lanthanides in each step of the process, with this organic phase only the HDEHP extracts molybdenum, whatever the acidity of the aqueous phase. Unlike lanthanides or americium, speciation of molybdenum in the aqueous phase varies depending on the experimental conditions (pH, concentration of molybdenum). Extraction mechanisms are in principle different for each species. At high acidity, Mo is well simulated by using a Mo(DEHP)2 organic complex. On the other hand, low acidity leads to a more complicated chemistry of molybdenum involving various species in aqueous and organic phases. For this study, over a range of pH greater than 1, it was decided to limit to three species (one cation, one anion and one neutral species): MoO42-, MoO3 and MoO22+. Therefore, the intermediate species, dimers and polymers are initially represented by with one of those three species. Molybdenum is extracted by one of three types of mechanisms, depending on pH value: cation exchange, extraction by solvation or anion exchange. It should be noted that experimentally only the MoO2DEHP2HDEHP2 complex was identified in the organic phase. Experiments were used to determine the values of the constants associated with equilibrium. The model was implemented in the PAREX simulation code to design flowsheets. The calculation results were compared with experimental data from tests carried out in mixer-settlers. The comparison showed the good accuracy of the model. It can be used to predict behavior of the chemical system, including changes in pH associated with the extraction and back-extraction of Mo at low acidity. This modeling can be easily adapted to other separation processes, such as rare earth extraction processes, for which it is necessary to manage molybdenum as an impurity

Water Soluble PDCA Derivatives for Selective Ln(III)/An(III) and Am(III)/Cm(III) Separation

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Towards a new GANEX 2nd cycle process for the co-separation of TRU

International audienceWe report first results on the development of a new system for the GANEX 2 nd cycle: A solvent consisting of N,N,N',N'-tetra-n-octyl-diglycolamide (TODGA) + N,N'-dimethyl-N,N'-dioctyl-2-(2-hexyloxyethyl)malonamide (DMDOHEMA) in kerosene was developed which co-extracts TRU and lanthanides with high distribution ratios and allows for Pu(IV) loading up to 35 g/L. Also the behaviour of non-lanthanide fission products was studied. A substitute for oxalic acid (used as Zr masking agent in DIAMEX processes but not useful in the presence of Pu(IV)) had to be found: CDTA efficiently suppresses the extraction of Zr and also masks Pd which would otherwise be co-extracted. In the selective TRU strip section actinides are back-extracted into an aqueous solution containing a hydrophilic 2,6-bis(1,2,4-triazin-3-yl)pyridine (BTP) and acetohydroxamic acid (AHA) in nitric acid. Lanthanides are kept in the organic phase by a sufficiently high nitric acid concentration; no salting out or buffering agents are required