Multiparametric Investigation of the Reactions of Plutonium under Estuarine Conditions

Abstract

Several sampling campaigns were carried out in the Seine estuary in order to study the behaviour of plutonium isotopes versus salinity ( 23 "Pu and 239 ' 240 Pu), in 0.45 μηι filtered waters. During estuarine mixing, the plutonium has a non-conservative behaviour: plots of Pu activities versus salinity display an excess of dissolved 238 Pu (RI = «"p u / 2! " 4°P u > 1) in low salinity waters (0.5 and 1.5 g Γ 1 ) and a depletion (RI < 1) in the zone of intermediate salinities (8 to 15 g Γ')> with respect to conservative dilution.Laboratory experiments showed that Pu(V) present in seawater is reduced to the III, IV states and sorbed onto particles with a maximum in low salinity waters which could explain the depletion observed at intermediate salinity in the Seine estuary. Reduction occurs prior to sorption and is connected with the Seine river colloidal and dissolved species (humic acids). The Pu associated with estuarine sediments desorbs from the "oxidehydroxide" fraction in contact with river water, thus partly explains the plutonium excess measured in low salinity filtered waters of the Seine.

Prognosticating the humic complexation for redox sensitive actinides through analogy, using the charge neutralisation model

“…calculations and does not take into account the redox properties of HS, and cannot be considered as strict representation of actinide comportment in the presence of HS. The most striking example is the lack of plutonium (VI) humic complexation when pH ≥ 4.5 as it has been observed in sea water [12].…”

“…Comm.]. This cannot be considered as representative of plutonium (VI) comportment in sea water [12]. Furthermore, one can notice that there is a marked difference between the experimental data form different authors for uranium (VI) under low CO 2 (g) partial pressure.…”

“…Experimental difficulties have often prevented from obtaining reliable results on reduced states of uranium, neptunium or plutonium. Furthermore, the redox properties of humic substances [3][4][5] have led to confusing results for protactinium [6], neptunium [7,8], plutonium [9][10][11][12] and other elements [13][14][15][16][17][18][19], even if the use of ligands to stabilise redox state is well known in the nuclear industry [20][21][22][23]. Otherwise, the reduction of uranium (VI) by HS has not been clearly observed up to now [24][25][26].…”

Évolution spatio-temporelle des concentrations, des rapports isotopiques et des facteurs de concentration du plutonium dans une espèce d'algue et deux espèces de mollusques en Manche

“…Le plutonium peut présenter plusieurs états de valence dans les eaux naturelles, Pu(V,VI) étant essentiellement associé à la fraction filtrée (< 0,45 pm), Pu (IIIJV) étant essentiellement associé à la fraction particulaire (> 0,45 pm). La concentration molaire du plutonium dans la fraction filtrée (< 0,45 pm) est de l'ordre de 10-'s*'M (Garcia et al, 1996). Cependant, le plutonium, comme les autres éléments transuraniens, est considéré comme non conservatif au sein de la masse d'eau, puisqu'il est éliminé de celle-ci par précipitation directe ou fixation sur la matière particulaire (Condren et al, 1996).…”

Complexation of Radionuclides with Humic Substances

“…Moreover, an enhancement of Pu(V) reduction is observed in the presence of light and divalent cations, compared to experiments conducted in the dark without divalent cations [50]. Pu reduction to the IIIand IV-valent states has also been observed under estuarine conditions in the presence of colloidal and dissolved species of HA [51]. For anoxic waters, complexation by HS will be the predominant phenomenon for both Pu(III) and Pu(IV).…”