Thorium oxide dissolution in HNO-HF mixture; Kinetics and mechanism

Simonnet, M.   ; Barr, N.*; Drot, R.*; Le Naour, C.*; Sladkov, V.*; Delpech, S.*

Simonnet, M.; Barr, N.*; Drot, R.*; Le Naour, C.*; Sladkov, V.*; Delpech, S.*

This paper is an attempt to find out thorium oxide dissolution mechanism in HNO-HF mixture. In a previous paper, several parameters effects on thorium oxide dissolution have been described, with specific focus on hydrofluoric acid effect, which can lead to an increase of the dissolution rate if present in small amount, but precipitates as ThF at higher content. Based on this previous study, experimental data were fitted using several dissolution models in order to find out the best one. Finally, a revisited model based on literature and considering the ThF formation was proposed. It describes the main steps of dissolution and is able to fit the experimental data for a wide range of solution compositions. This point is crucial since it allows considering an extrapolation of the established model to not-yet-studied conditions.