Experimental investigation of thermal stratification development in boiling water reactor suppression pools during reactor core isolation cooling system operation

Abstract

The Reactor Core Isolation Cooling (RCIC) system provides make-up water to the reactor pressure vessel during isolation events by passing steam from the vessel through a turbine which drives a pump to return water to the vessel. Exemplary performance of the RCIC system during the Fukushima Daiichi nuclear accident of 2011 has promoted interest in its potential performance.To investigate the development of thermal stratification within suppression pools due to RCIC system exhaust, a facility was constructed to produce the highest-resolution 3-D temperature measurements available in a large water pool during pool mixing by steam injection.Thermal stratification was most strongly influenced by suppression chamber pressure. Increased steam flowrate promoted mixing, which delayed the onset of thermal stratification. Containment response is discussed with respect to thermal stratification, which delays the time of warm water ingestion and cavitation of the RCIC pump, and pool mixing, which reduces the containment pressurization rate.