| Abstract Scope |
Recent developments in nuclear fuel industry have been focused on increasing safety, especially during accidental conditions. In this endeavor, doping with various elements (Cr, Nb, Gd, Al) is used to fine tune fuel properties, such as for Chromium Doped Fuel (e.g. grain size) which is commercialized as an Accident Tolerant Fuel. The present study, involving Framatome and CEA aims at providing a more complete view of chromium behavior in a UO2/U3O8 blend and its evolution during sintering. The vast majority of existing literature on Cr2O3-doped UO2 deals with reducing environment akin to sintering conditions for UO2 (-510 < ΔḠO2< -390 kJ/mol - 1700 °C) but does not involve transformations under oxidizing atmospheres. First, production scraps or defective pellets are oxidized from UO2 into U3O8 and reintroduced as additive in the pellet blend. In addition, during sintering, U3O8 is reduced to UO2, generating water vapor locally hence modifying oxygen potential in the surrounding atmosphere. Many unknowns remain regarding chromium integration in U3O8, UO2+x lattices during the sintering. Some authors showed a change in Oxygen/Metal ratio at high oxygen partial pressures and 900 to 1100 °C, not otherwise mentioned in literature. This brings a need for a better understanding of U-Cr-O behavior under these oxidizing atmospheres (UO2+x domains), which is the aim of this study. In order to shed some light onto Cr interaction with UO2/U3O8, UO2 doped pellets are manufactured under controlled oxygen pressure. Subsequent characterization (TGA, SEM, XRD, XAS) are used to bring more thorough understanding of U-Cr-O system. |