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|All Authors / Contributors:||
Olivier Guigou; Eric Simoni; Université de Paris-Sud. Faculté des Sciences d'Orsay (Essonne).
|Description:||186 p. : ill. ; 30 cm.|
|Responsibility:||Olivier Guigou ; sous la direction de [Eric Simoni].|
PUREX process for recycling nuclear used fuel is based on a series of redox reactions coupled with the difference in extraction of the various oxidation states of actinides by tri-n-butylphosphate (TBP). However, the existence of oxidizing species (in particular HNO2) in the biphasic system is responsible for "parasitic" reactions involving a thermodynamic instability of Uranium(IV) and Plutonium(III). The principal objective of this work is to consolidate knowledge of redox chemistry of U and Pu in aqueous (acid nitric) and organic (TBP30%/n-dodecane) mediums. The experimental parameters required in order to obtain kinetically exploitable data are established. In nitric aqueous and organic medium, oxidation of U(IV) by nitrous acid is governed by an autocatalytic mechanism. The production of nitrous acid is proportional to the oxidized quantity of uranium(IV). The variation of the concentrations of nitrous acid during reaction largely diminishes the number of exploitable data. It nevertheless was checked, in aqueous medium, increasing speeds with uranium(IV), nitrous acid and nitrate concentrations ; a reduction is obtained when acidity increases. In organic medium, it is proposed experimental conditions favorable to obtain the useable results. The study of the stability of Pu(III) in nitric organic medium shown that Pu(III) is a fugacious species at ambient temperature. Its stabilization requires specific experimental and chemical conditions. Experimental acquisitions make it possible to check on the one hand the autocatalytic character of Pu(III) oxidation, and on the other hand the influence of initial Pu(III) concentrations.