b'Sintering high uranium density fuels in a flashPrincipal Investigator: Rubens Ingraci NetoTeam Members/ Collaborators: Darrin Byler, Ken McClellan and Erofili KardoulakiUranium dioxide pelletsN uclear fuels with high thermaldamages to the pellets. In addition, conductivity, and elevatedthe DC electric field used for the FS with good mechanicalmelting point, such as UN, areexperiments induced oxygen vacancy integrity and densitiesan alternative to traditional UO 2thatmigration and overheating of the up to 94 %TD werecan contribute to the safe operation ofcathode causing a geometric distortion obtained in less thanthe reactor [1, 2]. Furthermore, UNof the pellet as well as an O/M gradient 30 minutes usinghas high uranium density which allowsalong the pellet. These results suggest current controlled flashhigher burnup and long-life operationthat controlling the FS parameters sintering with alternate[3].However, sintering of UN requiresis vital to achieve dense pellets with electric fields. temperatures greater than 2100 Cgood mechanical integrity. Therefore, and sintering times of about 10 h tothe first stage of this study aimed to achieve 95% of its theoretical densityanalyze how the FS parameters, mainly (TD) [4]. Furthermore, UN is prone tothe electric current and electric field oxidation and reaction with steam [5,waveform, affect the sintering kinetics 6, 7]. Recently, UO 2 -UN compositesof UO 2.16 . By controlling these FS with small additions of UN have beenparameters, UO 2.16pellets with good considered density fuel alternativemechanical integrity and up to 94 %TD due to the oxidation resistance that iswere obtained. These FS conditions expected to be provided by the UO 2 were then applied to experiments with [8, 9]. Although, this composite is stillUO 2.00 + 10 vol% UN composites.difficult to sinter. Flash sintering (FS),Accomplishments:a field assisted sintering techniqueThe densification of UO 2.16pellets (FAST) that combines electric fieldsduring FS, at controlled current rates, and currents, has been shown to drasti- is compared in Figure 1 with that cally reduce the sintering times andduring conventional sintering (CS) at temperatures of nuclear fuels. different heating rates (2, 5, and 10 C Project Description: min-1 up to 1600 C). For all FS tests, In this study, FS has been investigatedthe furnace was heated up to 600 C. for densification of UO 2.00+ 10 vol%Following this, an AC electric field UN composites. Previously, Valdez et al.was applied and the current flowing [10] used FS to obtain UO 2.16pellets upthrough the sample was increased to 91 %TD, although, these pellets werelinearly in a controlled manner up to severely cracked due to high thermal12 A (RMS). As shown in Figure 1, FS gradients that developed. During theat 32 mA mm-2 min-1 led to 94%TD in traditional FS method used by Valdez25 min in contrast to 92 %TD afteret al. [10], the electric current flowing14 hours of CS at 2 C min-1.through the pellet increased from 0During controlled current rate AC-FS A to ~ 11 A in a fraction of second.of UO 2.16 , it was observed that the This uncontrolled current surge ledlowest current rate (32 mA mm-2 to rapid Joule heating and consequentmin-1) led to reactions near the elec-58 2020|AFC ACCOMPLISHMENTS'