Off-take, slugging, liquid holdup, and condensation heat transfer critical to mid-loop operation

Abstract

Three separate effect tests are performed to investigate thermal-hydraulic phenomena found in reactor coolant system in case of the loss-of-residual-heat-removal (LORHR) during mid-loop operation: off-take and slugging at the surge inlet in the hot-leg, two-phase mixture level in the pressurizer and condensation heat transfer in the U-tube. The test facilities are designed according to the scaling analysis so as to maintain scale similarities with the prototypes of nuclear power plant. A scale methodology proposed by the present study satisfies the preservation of parameters for off-take and mixture level. New experimental data and correlations are obtained through those separate-effect tests, which are used for the modifications of models in the RELAP5/MOD3 code. Modified correlations are implemented into the RELAP5/MOD3 and assessed. The effect of tube diameter is investigated using the condensation heat transfer data in the U-tube. It turns out that the flow parameter governing condensation heat transfer with noncondensible gas is the mixture Reynolds number. The off-take and slugging in the hot-leg with the surge line are experimentally tested using the off-take test facility. The scaling analysis is performed to scale down the test facility. The experimental results are categorized into three items: onset of off-take (liquid entrainment) at the branch pipes, onset of slug transition in the horizontal pipe and discharge quality at the branch pipes. It is found out that the scale effect of the branch diameter on the onset of liquid entrainment is small. While the existing correlation of onset of liquid entrainment well predicts the present data, the Taitel-Dukler correlation for the onset of slug transition does not. The onset of slug transition shows its strong influence on the discharge quality. A new correlation for onset of slug transition is developed and implemented into RELAP5/MOD3. The discharge quality is strongly affected by the flow regime - stra...