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AbstractAbstract
[en] The PUREX process is a solvent extraction method dedicated to the reprocessing of irradiated nuclear fuel in order to recover pure uranium and plutonium from aqueous solutions of concentrated nitric acid. The tri-n-butylphosphate (TBP) is used as the extractant in the organic phase. The aim of this thesis work was to improve the modeling of liquid-liquid extraction media in nuclear fuel reprocessing. First, Raman and 14N NMR measurements, coupled with theoretical calculations based on simple solutions theory and BIMSA modeling, were performed in order to get a better understanding of nitric acid dissociation in binary and ternary solutions. Then, Pu(IV) speciation in TBP after extraction from low nitric acid concentrations was investigated by EXAFS and vis-NIR spectroscopies. We were able to show evidence of the extraction of Pu(IV) hydrolyzed species into the organic phase. A new structural study was conducted on An(VI)/TBP and An(IV)/TBP complexes by coupling EXAFS measurements with DFT calculations. Finally, extraction isotherms modeling was performed on the Pu(IV)/HNO3/H2O/TBP 30%/dodecane system (with Pu at tracer scale) by taking into account deviation from ideal behaviour in both organic and aqueous phases. The best modeling was obtained when considering three plutonium (IV) complexes in the organic phase: Pu(OH)2(NO3)2(TBP)2, Pu(NO3)4(TBP)2 and Pu(NO3)4(TBP)3. (author)
[fr]
En France, le traitement des combustibles nucleaires irradies repose sur le procede PUREX au cours duquel l'uranium et le plutonium sont extraits selectivement par le TBP a partir d'une solution aqueuse concentree d'acide nitrique. L'objectif de ce travail de these etait d'aboutir a une meilleure modelisation des milieux de traitement du combustible irradie. Dans un premier temps, des mesures Raman et RMN 14N, couplees a des calculs bases sur la theorie des solutions simples et sur le modele BIMSA, ont permis de completer les connaissances actuelles sur la dissociation de l'acide nitrique dans des solutions binaires et dans des melanges ternaires. Dans un deuxieme temps, la speciation de Pu(IV) dans le TBP apres extraction a faible acidite a ete etudiee par EXAFS et spectrophotometrie vis-NIR, ce qui a permis de mettre en evidence l'extraction d'especes hydrolysees de Pu(IV) en phase organique. En parallele, une nouvelle caracterisation structurale des complexes An(VI)/TBP et An(IV)/TBP a ete effectuee en couplant des mesures EXAFS a des calculs de chimie quantique. Enfin, la modelisation du systeme Pu(IV)/HNO3/H2O/TBP 30%/dodecane a ete effectuee en prenant en compte les ecarts a l'idealite dans chaque phase. La meilleure modelisation de l'extraction de Pu(IV) a l'etat de trace a ete obtenue en considerant l'extraction de trois complexes de plutonium: Pu(OH)2(NO3)2(TBP)2, Pu(NO3)4(TBP)2 et Pu(NO3)4(TBP)3Original Title
Modelisation de l'extraction de Pu(IV) et speciation de HNO3 dans le traitement du combustible irradie
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12 Nov 2012; 218 p; 194 refs.; Available from the INIS Liaison Officer for France, see the 'INIS contacts' section of the INIS-NKM website for current contact and E-mail addresses: http://www.iaea.org/inis/Contacts/; Sciences Chimiques
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Report
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Thesis/Dissertation
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