Assessment of performance of BWR passive safety systems in a small break LOCA with integral testing and code simulation

► A SB LOCA test is performed for a natural circulation and passively safe BWR. ► Passive safety systems function as design to mitigate the LOCA. ► Core is not uncovered and containment is not over-pressurized in this LOCA test. ► RELAP5/Mod3.3 successfully simulates this LOCA on facility and plant level. An integral test simulating a postulated Small Break Loss Of Coolant Accident (SB LOCA) has been conducted on a scaled-down test facility, Purdue University Multi-Dimensional Integral Test Assembly (PUMA). This test aims to simulate the hypothetical Bottom Drain Line Break (BDLB) accident initialized by an instantaneous guillotine rupture of the vessel Bottom Drain Line (BDL) in a generic design of natural circulation BWR equipped with passive safety systems. The objective of this research is to evaluate the ability of passive safety systems in this BWR to keep core from uncover and containment from overpressure during a SB LOCA transient by reproducing the LOCA transient in the test facility. The integral test simulates the interaction of reactor components and demonstrates the functionality of passive safety systems, such as Emergency Core Cooling System (ECCS) and Passive Containment Cooling System (PCCS). The experimental results showed that the two most important safety criteria were satisfied: the core coolant level was always higher than the Top of Active Fuel (TAF) and containment pressure did not exceed the design limit during this SB LOCA. The scaling principle of the test facility and RELAP5/Mod3.3 code capability were evaluated through the comparison between the experimental data and the code simulation.