Gamma Radiation‐Induced Degradation of Acetohydroxamic Acid (AHA) in Aqueous Nitrate and Nitric Acid Solutions Evaluated by Multiscale Modelling

Abstract

Acetohydroxamic acid (AHA) has been proposed for inclusion in advanced, single‐cycle, used nuclear fuel reprocessing solvent systems for the reduction and complexation of plutonium and neptunium ions. For this application, a detailed description of the fundamental degradation of AHA in dilute aqueous nitric acid is required. To this end, we present a comprehensive, multiscale computer model for the coupled radiolytic and hydrolytic degradation of AHA in aqueous sodium nitrate and nitric acid solutions. Rate coefficients for the reactions of AHA and hydroxylamine (HA) with the oxidizing nitrate radical were measured for the first time using electron pulse radiolysis and used as inputs for the kinetic model. The computer model results are validated by comparison to experimental data from steady‐state gamma ray irradiations, for which the agreement is excellent. The presented model accurately predicts the yields of the major degradation products of AHA: acetic acid, HA, nitrous oxide, and molecular hydrogen.

Multiscale Modeling of Plutonium Radiation Chemistry in Nitric Acid Solutions. 1. Cobalt-60 Gamma Irradiation of Pu(IV)

“…The radiation-induced chemistry occurring in each of these time regimes is distinctly different and can be influenced by the presence of solutes . Such predictive models can provide significant fundamental insights into the underlying mechanisms of an irradiated system. − For example, multiscale computer models have been developed and successfully used to interpret and predict radiation-induced changes in the oxidation state distribution of plutonium’s adjacent neighbors, neptunium and americium, in aqueous nitric acid (HNO 3 ) solutions , the prototypical solvent for actinide manipulations in nuclear fuel cycle technologies. The reported calculations accurately reproduced the experimental behavior and confirmed the fundamental radiation-induced mechanisms responsible for the observed changes in the oxidation state distribution of both actinides.…”