Loss-of-flow transients in the liquid metal-cooled reactor-pool experiment E-SCAPE

Natural circulation in the primary system is one of the key mechanisms for removing the decay heat in the MYRRHA pool-type research reactor under development at SCK CEN, the Belgian Nuclear Research Centre. To confirm the feasibility of this passive approach, experiments are performed in the E-SCAPE facility, a thermal hydraulic 1/6-scale 3-D model of the primary system of MYRRHA, with an electrical core simulator and cooled with Lead Bismuth Eutectic. This paper presents the outcome of transient loss-of-flow (LOF) experiments in E-SCAPE. First, the representativeness of LOF transients in E-SCAPE for MYRRHA is demonstrated based on simplified analytical integral models of the reactor prototype and of the scaled facility. Next, results of several test cases with varying core powers and system pressure losses are reported. In all cases studied, a smooth transition from forced to buoyancy-driven natural circulation is observed after the LOF event, with the establishment of stable, lower flow rates. Decay heat can be safely removed from the core as the maximum core temperatures stay within safety limits. Two phases can be identified during the transient: an initial phase dominated by mass inertia, and a second phase dominated by the heat capacity of the system. The final steady state shows significant thermal stratification in the upper plenum. The extensive instrumentation in the E-SCAPE facility allows direct comparison of experimental data with numerical simulations, allowing validation of simulation tools in representative conditions. This is essential for the safety assessment and licensing process of MYRRHA.