Quenching Temperatures During Reflood Transients in a Rod Bundle

Abstract

During reflood transients, drastic changes in the boiling regime occur at the quenching temperature, where liquid can reestablish physical contact with a hot solid surface. A comprehensive understanding of the quenching temperature and the factors affecting its behavior is essential for assessing the cooling of a rod bundle. In this study, constant reflood experiments were conducted at the NRC/PSU Rod Bundle Heat Transfer (RBHT) test facility to explore the impact of pressure and flooding rate on the quenching temperature and the associated boiling characteristics.

The reflood experiments explored in this study clearly show significant effects of flooding rate and pressure. A higher rate of flooding always leads to a faster quenching of the rod bundle. For a given flooding rate, however, the quenching temperature (T_q) tends to vary across the bundle, increasing from lower to higher elevations due to skewed power profiles and enhanced local flow effects. Pressure has a significant impact on the quenching temperature (T_q), especially at lower elevations, where the quenching temperature tends to increase as pressure increases.

The effect of flooding rate on T_q depends on the elevation and flow rate. At low elevations, the quenching temperature (T_q) tends to increase with the flooding rate regardless of whether the flooding rate is high or low. At high elevations, the T_q behavior varies differently with the flooding rate.