RESUMPTION OF NATURAL CIRCULATION DURING POST-BCM REFILLING IN A BW PRESSURIZED WATER REACTOR

摘要

A phenomenological description of the thermal-hydraulic behavior of a Babcock & Wilcox (B&W) pressurized water reactor (PWR) during the refilling transient following an SB-LOCA is presented. The refilling of the system is obtained by activation of the high pressure injection (HPI) when the primary system has reached steady-state boiling condensing mode (BCM) conditions. A boron-depleted volume is generated in the steam generators during BCM, and the resumption of flow during refilling would cause it to move towards the core, where it would cause an increase in reactivity. An extensive experimental program conducted at the University of Maryland showed that the system spontaneously resumes natural circulation towards the end of the refilling phase. The behavior of the system before and after the flow resumption has very important implications on the boron mixing issue, as it determines the size and mixing of the boron-depleted volumes put in motion. Other observations about the system's behavior are presented, such as the occurrence of interruption resumption mode (IRM) during HPI refilling, and the impact of asymmetric refilling on the development of thermal hydraulic phenomena.