Behavior of UO 2 in the RBMK-1000 Spent Fuel under Oxidizing Conditions

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Behavior of UO2 in the RBMK-1000 Spent Fuel under Oxidizing Conditions A. B. Kolyadin, V. Ya. Mishin, K. Ya. Mishin, A. S. Aloy and T. I. Koltsova RPA, V.G. Khlopin Radium Institute, St. Petersburg, Russia, E–mail: [email protected] ABSTRACT The oxidation of UO2 –type spent nuclear fuel (SNF) in gaseous media was studied at different temperatures and oxygen contents using gravimetric and powder X-ray diffraction (XRD) techniques. The aim of the study was to determine the mechanism(s) of thermal-oxidation alteration of SNF during long-term dry storage. The samples used in the experiments were chips of RBMK-1000 fuel rods. Oxidation of UO2 with a mean burn-up of 10.7 and 19.73 MW d/kg in humid air was observed at a temperature as low as 150°С. At 200°С nearly all of the UO2 was transformed into U3O8 between 3500-4000 hours. In a humid nitrogen environment containing of 0.05-1.3 vol. % oxygen at 300°С, the UO2 completely transformed to U3O8 between 2500-3000 hours. Oxidation of UO2 in samples with small amounts of jacket damage (e.g.,