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Influence of thermodynamic database on the modelisation of americium(III) speciation in a simulated biological medium

Bion, L.a , Ansoborlo, E.b , Moulin, V.c , Reiller, P.a , Collins, R.d , Gilbin, R.e , Février, L.e , Perrier, T.e , Denison, F.e , Cote, G.f
Radiochimica Acta
Volume 93, Issue 11, 2005, Pages 715-718


An intercomparison exercise was led in order to study the impact of thermodynamic database (TDB) on the speciation of americium(III) in biochemical media. A first exercice was led, considering only the americium(III) species in solution. Even with different data sets, all the exercises are in relatively good agreement, concluding to successive complexation of the radioelement by phosphate (pH range from 0 to 3), citrate (pH range from 3 to 8) and hydroxo-carbonate (pH range from 8 to 14). Nevertheless, the speciation of americium differs for each pH range from one work to an other. These results are still observed when the speciation calculation includes the formation of solids. Nevertheless, some workers did not integrate in their data set the formation constant of Am(PO4). This solid is known to be very insoluble in typical biological media. All the calculations where Am(PO 4) was not in the TDB presented a speciation where americium is solvated (mostly under citrate forms). When the formation of Am(PO4) is considered, the actinide is quantitatively present under this solid species. This work is a representative example of the impact of the thermodynamic data used in speciation exercises. Some exercices, using uncompleted TDB had wrong results and led to the conclusion of the necessity in the use of expertised and extended TDB.

a CEA Saclay - DEN/DPC/SECR/LSRM, Bât. 391, 91191 Gif sur Yvette Cedex, France
b CEA Marcoule - DEN/DRCP/CETAMA, Bât. 181, 30207 Bagnols sur Cèze, France
c CEA Saclay - DEN/DDIN, Bât. 121, 91191 Gif sur Yvette Cedex, France
d CEA Saclay - DSM/DRECAM/LPS, 91191 Gif sur Yvette Cedex, France
e IRSN - DPRE/SERLAB/LRE, Centre de Cadarache, 13115 Saint-Paul-les-Durance, France
f ENSCP, 11 rue Pierre et Marie Curie, 75005 Paris, France


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