IIST and BETHSY Counterpart Tests on a PWR Total Loss-of-Feedwater Transient with Two Different Bleed-and-Feed Scenarios

Abstract

The thermal-hydraulic phenomena and recovery actions of loss-of-feedwater (LOFW) incidents in a pressurized water reactor were investigated experimentally at the Institute of Nuclear Energy Research Integral System Test (IIST) facility. To understand whether the physical phenomena observed in the full-height and full-pressure facility during an LOFW transient can be simulated in the reduced-height and reduced-pressure IIST facility, two counterpart tests based on the same scenarios as those of the BETHSY tests were performed. These two tests performed in BETHSY differ mainly at the initiation of the bleed-and-feed process on the primary side in order to examine the effectiveness of recovery measures on the processes of the pressurizer power-operated relief valves early and late opening. The initial and boundary conditions of the current tests were determined by scaling down the corresponding conditions of the LOFW experiments performed at BETHSY. In view of the inherent differences in design, scaling approach, and facility operation conditions in the systems, the consistency between the counterpart tests is examined by identifying key thermal-hydraulic phenomena and clarifying their differences. The results of the IIST and BETHSY tests showed the common thermal-hydraulic behaviors of key parameters, such as system pressure, void fraction in the hot leg, primary coolant inventory, pressurizer level, and discharged mass evolutions. The chronological events studied in the IIST facility are generally consistent with those studied in BETHSY. The results from the IIST facility may not be exact replications of the BETHSY response; however, the physics involved in bleed-and-feed are well measured and modeled.