Investigation of dissolution behavior of Mo-CerMet fuel in reprocessing by means of nano-electrospray ionization mass spectrometry

Abstract

Dissolution behavior of Mo-CerMet fuel in reprocessing was investigated by use of nano ESI-MS. Pure Mo solution as well as 4 mixed systems (Mo-Fe, Mo-Zr, Mo-Th and Mo-Eu) solutions are qualitative and quantitative analyzed in 0.5 - 3 mol/L nitric acid. In the pure Mo solutions, Mo dimer is the dominant species in the sample of 1 mol/L and 3 mol/L nitric acid, at lower acid concentration 0.5 mol/L nitric acid, the tendency towards formation of polymeric species increases. The solution species are measured during the dissolutions of the Mo pellet. With increasing concentration of Mo and increasing dissolution time, larger polymeric species form. The species distribution becomes more complicated during dissolution of the pellet, due to the increasing Mo concentration. Therefore, we can conclude that higher acidic strengths and low Mo concentration are favorable to the reprocessing step. The addition of Fe(III) nitrate not only lead to significantly increase of the solubility of molybdenum and dissolution rate in nitric acid but also the formation of Mo-Fe species prevents formation of precipitates. Throughout the three mixed system Mo-Zr, Mo-Th and Mo-Eu, higher acidic strengths and the presence of Zr, Th or Eu suppresses the formation of pure Mo species and the formation of large Mo polymeric species. High concentration of nitric acid can suppress the formation of mixed Mo-Th species and mixed Mo-Eu species. In contrast, in higher concentration of nitric acid more mixed Mo-Zr species are formed. This could be due to the particularity of the ZMH precipitate precursors. Since each species could behave differently in liquid-liquid extraction steps, solutions containing less different species are easier to be handled in reprocessing. Working at higher acid strengths could be advantageous for future reprocessing processes, as there are significantly fewer dissolution species in the system.