Oxidation behavior of UO in air

Suzuki, Kiichi  ; Nelson, A. T.*; Sunaoshi, Takeo*; McClellan, K.*; Kato, Masato   

In a reactor core or a spent fuel pool loss of coolant accident, fuel cladding may be breached and cause rapid oxidation of UO pellets. Oxidation of UO results in pulverization of the pellet and significant evaporation of UO, possibly leading to spread of nuclear material to the environment. Therefore, understanding the oxidation behavior of UO is an important factor. In this study, the oxidation behavior of UO pellets and powders in air was investigated over a wide temperature range. Isothermal oxidations were carried out from 673 to 1923 K. Oxidative pulverization was observed below 1073 K. The weight gain rate at 773 K was larger than that at 873 K, suggesting the oxidation mechanism might change in this regime. Rapid weight loss was observed above 1723 K. The vapor pressure of each phase in the U-O system was calculated, indicating that volatilization of UO was likely responsible for the measured weight loss. The evaporation rate of UO for a urania pellet was then evaluated.