Bare Rod Hydraulic Performance in Hexagonal Array Rod Bundles

In a recent publication in Applied Thermal Engineering, National Tsing-Hua University (Hsinchu, Taiwan) scientists: Professor Shih-Kuei Chen and Dr. Yu Min Chen from the Institute of Nuclear Engineering and Science, in collaboration with Professor Neil Todreas at the Massachusetts Institute of Technology demonstrated that their correlation for wire wrapped rod bundle pressure loss could also predict bare rod bundle data very satisfactorily. That wire wrapped correlation based on the original Cheng-Todreas (CTD) correlation of 1986 was named the Upgraded CTD (UCTD) correlation . Importantly it accomplished satisfactory prediction also of sixteen additional wire wrapped fuel bundle experiments have been performed worldwide since 1986 which provided data to supplement regions of minimal data in the bundle test data base.

The key to use of the UCTD correlation for bare rod bundle performance prediction is that even for wire wrap rod geometry its formulation requires that the bare rod bundle friction factor is calculated correctly. This is due to the fact the formulation of the friction factor for each type of subchannel are the bare rod values enhanced by wire effects. . It is noteworthy to mention that most of the available 32 bare rod bundle data used to validate the performance of UCTD in predicting bare rod bundle results in this study was based on experiments carried out by Rehme in early 1970’s.

In this recent publication the research team first carried out accuracy prediction for the turbulent regime where 30 out of the available 32 bundles had data in turbulent regime, and comparisons between the measured data in the turbulent regime and the prediction of UCTD with diameter set to zero was illustrated. The researchers then engaged in accuracy prediction in the laminar regime. Finally using data from the remaining 2 of the 32 bundles above, prediction accuracy for the transition flow regimes was undertaken.

The authors reported that their correlation predicted data from 30 bare rod bundles in the turbulent regime with a mean error of −0.6%, a standard deviation of 6.3% and a 90% confidence interval of ± 10.5%. Data in transition regime available for all 32 bundles was slightly over predicted, Finally, for the laminar regime, data from 12 of 32 bundles was available. Remarkably, the laminar prediction was surprisingly accurate, in that 10 out of 12 bundle laminar constants were predicted within 5% error with the remaining two within 10% error.

In summary, the study presented the evaluation of the bare rod data base consisting of 32 bundles tested before 1980. Overall, in a statement to Advances in Engineering, Professor Shih-Kuei Chen, the corresponding author highlighted that the accuracy of the prediction of the pressure drop in a bare rod hexagonal bundle by the upgraded Cheng and Todreas correlation was demonstrated to be excellent using the 32 bundle experimental bare results available in the literature.