Design and control of the oxygen partial pressure of UO2 in TGA using the humidification system

The oxygen to uranium (O/U) ratio of UO2±x is determined by the oxygen content of the sample and is affected by oxygen partial pressure (pO2) of the surrounding gas. Oxygen partial pressure is controllable by several methods. A common method to produce different oxygen partial pressures is the use of equilibria of different reaction gases. There are two common methods: H2O/H2 reaction and CO2/CO reaction. In this work, H2O/H2 reaction using a humidifier was employed and investigated to ensure that this humidification system for oxygen partial pressure is stable and accurate for use in Thermogravimetric Analyzer (TGA) experiments with UO2. This approach has the further advantage of flexibility to make a wide range of oxygen partial pressure with fixed hydrogen gas flow rate only by varying temperature of water in the humidifier. The whole system for experiments was constructed and includes the humidification system, TGA, oxygen analyzer, and gas flow controller. Uranium dioxide (UO2) samples were used for experiments and oxygen partial pressure was measured at the equilibrium state of stoichiometric UO2.0. Oxygen partial pressures produced by humidification (wet gas) system were compared to the approach using mixed dry gases (without humidification system) to demonstrate that the humidification system provides for more stable and accurate oxygen partial pressure control. This work provides the design, method, and analysis of a humidification system for oxygen partial pressure control in experiments with oxide nuclear fuels.