Preliminary transient thermal-hydraulic analysis for new coated UN and UC fuel options in SCWR

When UO2 is used for SCWRs, the fuel centerline temperature might exceed the conservatively established industry accepted limit of 1850 °C because of low thermal conductivity of UO2 within the operating temperature range of Super Critical Water-cooled Reactors (SCWRs). In our previous study, Neutronic/thermal hydraulic coupled analyses are performed for a new advanced fuel design for SCWR. Uranium nitride (UN) coated with Zirconium carbide (ZrC) and uranium carbide (UC) coated with Silicon carbide (SiC) are proposed as advanced fuel option compared with traditional UO2. The present work is a further investigation aiming to evaluate the transient thermal-hydraulic behaviors for coated UN and UC fuel options. The coated UN, UC and traditional UO2 fuel are selected for the transient analysis. Typical transients of SCWR including partial loss of flow accident and reactivity insertion accident by decrease in feedwater temperature are performed. The TACOS code, which was developed for SCWR safety analysis in Xi'an Jiaotong University, is used in this study. The comparison of the transient thermal hydraulic characteristics is carried out between UO2 and the new coated fuels. The present transient studies cooperating with previous coupled neutronics/thermal hydraulic analyses reveal that coated UN and UC have good thermal behaviors in high temperature reactor like SCWR, much more work in other aspects needs to be done.