Steam oxidation of uranium mononitride in pure and reducing steam atmospheres to 1200 °C

The present study addresses the lack of steam oxidation kinetic data for high purity uranium mononitride (UN), assesses the sensitivity of the dynamic response of UN to the density of the monolithic sample exposed to flowing steam, as well as observes the variation in the oxidation kinetic response of UN to the presence of a common fabrication contaminant, carbon. In addition, the mass spectrometry performed on the evolved gas during the reaction with steam informs the reactions thermochemistry for UN with flowing steam during a thermal ramp and during an isothermal exposure at 500 degrees C. It is concluded here that high purity, high density samples, ( >= 94% theoretical density), have a significantly delayed onset of reaction with steam compared to values previously reported, the kinetic reaction is retarded in a reducing steam atmosphere (steam + 100 ppm H-2 ), and the reaction products are predominantly ammonia (NH3 gas) and UO2 at temperatures less than 700 degrees C, above which UO2+x (0.2 >= x >= 0.0) begins to form and NH3(g) dissociates. (c) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study provides steam oxidation kinetic data for high purity uranium mononitride (UN) at high temperatures, and observes the variation in the oxidation kinetic response of UN to the presence of carbon contaminants. The results show that high purity, high density UN samples have a delayed reaction time with steam and the reaction is suppressed in a reducing steam atmosphere, producing predominantly ammonia and UO2.