Application of a hydroxylamine nitrate stability model to plutonium purification process equipment

• Published in: Journal of loss prevention in the process industries 2015-05, Vol.35, p.12-18
• Main Authors: Barney, G. Scott, Duval, Paul B.
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Hydroxylamine stability; Kinetics; Mathematical models; Nitrates; Nitric acid; Oxidation; Plutonium; Process equipment; Reaction kinetics; Solvent extraction
• ISSN: 0950-4230; 1873-3352
• DOI: 10.1016/j.jlp.2015.03.004

A mathematical model that predicts hydroxylamine nitrate (HAN) (NH2OH·HNO3) stability is applied to aqueous solutions containing HAN, nitric acid and plutonium that are used in plutonium purification processes. The model estimates the stability of these solutions with respect to the rapid, hazardous, autocatalytic reaction of HAN with nitric acid that generates heat and gas. It also accounts for reaction kinetics, temperature changes, gas generation rates, solution volumes and flow rates, and distribution of plutonium and nitric acid between aqueous and organic phases. The model is applied to three typical process vessels used in solvent extraction purification of plutonium – a countercurrent aqueous/organic plutonium stripping column, an oxidation column used for HAN and hydrazine destruction, and a plutonium rework tank. Both normal and off-normal process scenarios are modeled. Two of the off-normal scenarios lead to the rapid autocatalytic reaction of HAN with nitric acid where heat and gas are generated and that could lead to damage of the process equipment and/or release of hazardous plutonium solution from the vessel. In these two cases, stationary aqueous solutions containing HAN, Pu(III), and nitric acid were allowed to slowly react until conditions for the autocatalytic reaction were reached. •Hydroxylamine nitrate stability in plutonium processing depends on temperature and solution concentrations.•A mathematical model was used to predict HAN stability in three typical process vessels.•The rapid autocatalytic decomposition reaction was not observed under normal operations.•Off-normal conditions (no aqueous flow) for two process vessels resulted in HAN instability.