Analysis of the Bubbly-Churn Regime Transition in a Scaled Model Boiling Water Reactor

A scaled model boiling water reactor (SMBWR) uses water at 0.095 MPa in a transparent heated channel 0.5 m in length with four electrical heated fuel simulator rods. The axial void profile in the channel is measured using conductivity probes. The boiling channel exhibits bubbly and churn flow regimes. In the present study, the bubbly-churn regime transition is investigated using the variance, kurtosis, and skewness of the probability density function (pdf) derived from the conductivity measurements. The positioning of five conductivity sensors along the boiling water channel allows examination of the gradual changes in the flow regime characteristics. The results indicate it is possible to detect the bubbly-to-churn flow regime transition using the pdf distribution attributes of the conductivity probes.