An experimental study of bottom rewetting in a rod bundle geometry

Abstract

The effect of various flow parameters on the rewetting velocity in a bottom rewetting phenomena has been experimentally studied in a 3×3 rod bundle geometry. The rod bundle geometry consisted of nine test rods surrounded by a radiatively heated square shroud. The rewetting tests were conducted at atmospheric pressures for low mass and heat flow ranges. Typical rewetting velocities measured in this study were in order to 1 to 5 mm/s. For a given test condition, an increasing inlet subcooling was accompanied by an increasing rewetting velocity. The rewetting velocity was first found to be decreased with increasing vapor quality until a critical value, for a given mass flux. For the vapor qualities higher than the critical value, the rewetting velocity was found to be increased with increasing vapor quality. For a given mass flux, the critical value of the vapor quality corresponded to the flooding limit of the flow. A Transient Reactor Analysis Code (TRAC) post-test calculation was performed for a subcooled inlet reflood test. The TRAC model considered only the test bundle and consisted of four components including ten fluid cells. The calculated and measured wall and vapor temperatures were the principle parameters for comparison. The precursory cooling rate above the quench front is found to be overpredicted by TRAC, resulting in overprediction of the rewetting velocity.