Influence of the concentration of nitric acid on the composition of NOX gas evolved during the dissolution of nuclear fuel and its implications on the PUREX process

Highlights: • NO_X gas composition was measured during UO₂ dissolution. • Predominant reaction by which UO₂ dissolves during anytime was identified. • Influence of nitric acid concentration on UO₂ dissolution was evaluated. Understanding the mechanism of dissolution of UO₂ in nitric acid is important for designing a continuous dissolution system for the reaction. Knowledge of the composition of the NO_X gas evolved during the course of the reaction is imperative for this understanding as it strongly influences the reaction mechanism. In this work, the profiles of the composition of NO_X gas evolved and the ratio of moles of acid consumed per mole of uranium dissolved during the dissolution of UO₂ pellets in nitric acid have been determined as a function of acidity. The predominant stoichiometric reaction by which UO₂ dissolves at every point of the reaction was clearly identified thereby improving the understanding of its mechanism and facilitates better control over the overall reprocessing process flowsheet.