A detailed reevaluation of the complexation equilibria of plutonium(IV) with the polyaminocarboxylic sequestering agent EDTA 4À has been performed in 1 M (H,K)NO 3 media at 298 K by means of visible absorption spectrophotometry and glasselectrode potentiometry at millimolar concentration levels. The high binding affinity even under strongly acidic conditions supports the exclusive formation of the neutral Pu(EDTA) complex over the range 0.01 [H + ] 0.9 M with an apparent formation constant of log b 110 ¼ 25.8(1) at 0.9 M HNO 3 . Extrapolation to zero ionic strength using the SIT approach provides the first ever-reported NEAeTDB compliant estimate of b 0 110 ðlog b 0 110 ¼ 32:2ð3ÞÞ. A global modeling procedure of the potentiometric data collected for three different metal over ligand ratios (1:1, 1:1.5, and 1:2) ascertained the formation of four additional species for pH values comprised between 2 and 6.5, namely [Pu(EDTA)(OH)] À , [Pu(EDTA) 2 H 2 ] 2À , [Pu(EDTA) 2 H] 3À , and [Pu(EDTA) 2 ] 4À . The visible absorption spectra for the first three complexes have also been determined. Data recorded above pH 3.5 (for a 1:1 molar ratio) or 6.5 (for a 1:2 molar ratio) were finally excluded from the global fitting procedure as speciation calculations suggested the precipitation of amorphous Pu(OH) 4(am) according to the latest critical value quoted in the literature for its solubility product. To cite this article:
RÉSUMÉWithin the framework of a seminar on environmental and health impact of tritium organized by article 31 Euratom expert group in November 2007, it was expected to make a point on tritium knowledge and to define R&D and regulatory axes. This document presents the different sources of tritium, different methods of measurement associated to tritium processes and survey, transfer in the biosphere compartments in normal and accidental conditions. It suggests some R&D subjects and discusses some regulatory aspects.
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