Preliminary Investigation of Preparing High Burn-Up Structure in Nuclear Fuel by Flash Sintering Using CeO_(2) as a Surrogate

The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.