Transient Boiling of Sodium in a Single-Pin Geometry under Loss-of-Flow Conditions

Abstract

Transient sodium boiling experiments have been conducted in an electrically heated single-pin annular channel under loss-of-flow conditions. Each run was made by reducing or stopping the flow at constant heater power. Records were obtained of the changes of temperatures, flow rates, pressures and voids. The experimental results were compared with analytical calculations. There was no strong effect of temperature ramp rate on the incipient-boiling (IB) wall superheat in the range of the present experimental conditions. The pressure rise at the initial vaporization compared well with the vapor pressure corresponding to the IB wall superheat. The pressure pulse occurred at the vapor collapse correlated reasonably well with the collision velocity between the re-entrant liquid columns, but the measured value was less than the theoretical value predicted from the sodium hammer analysis. The observed voiding pattern agreed fairly well with the calculation by the NAIS-P2 code (single-bubble slug expulsion model). The initial expulsion acceleration of liquid agreed well with the theoretical prediction from the one-dimensional liquid column expulsion analysis. The thickness (0.05 and 0.29 mm) of the residual liquid film became thinner with higher IB wall superheat.