Temperature measurements of thermal stratification and turbulent mixing in nuclear systems with a single heated jet

Large volumes or enclosures are utilized in nuclear systems such as the sodium fast reactor (SFR) upper plenum, spent fuel pools, and containment structures seen in common nuclear reactor designs. These volumes may be quiescent or turbulent the injection of a hotter or cooler jet of fluid. This can lead to turbulent mixing of the entire volume or thermal stratification of a hotter layer of fluid. Due to the large thermal gradients experienced by the structures due to a stratified volume, the structures can experience degradation which can lead to severe consequences such as a loss of coolant accident. In order to prevent or mitigate these consequences, computational fluid dynamics (CFD) codes can be utilized to predict the occurrence of turbulent mixing and thermal stratification. This data can be used in conjunction with structural analysis codes to determine the severity of phenomena occurrence on structures. Unfortunately, the validity of CFD codes to predict this type of behavior is limited due to the lack of experimental data to validate the predicted behavior. In response, the twin jet water facility (TJWF) created by the University of Tennessee was repurposed to create data sets of temperature using thermocouples and particle image velocimetry (PIV) for this effort. The temperature data collected using the thermocouples is similar to previous experiments conducted within an older version of the facility with a different geometric configuration. The most recently collected data was created by conducting several runs of each each set of experiment conditions and ensemble averaged. This was done to confirm the observed behavior is due to the physical processes and not due to noise or random happenstance. The spectral frequency responses of the temperature data were determined to observe frequencies or spectral behavior corresponding to turbulent mixing and stratification. The temperature and frequencies are reported to compare the experiments to simulations being conducted in conjunction with this study.