PERSEO was built at SIET laboratory (Piacenza, Italy) to study a new passive decay heat removal system operating in natural circulation. The main innovation in PERSEO is the presence of two pools connected by a line with a triggering valve. In this way it is possible to fill the pool where the emergency heat exchanger is located only when it is needed for safety reasons by using the water stored in a second separate pool. The operating parameters of PERSEO are characteristic of a generic boiling water reactor (BWR) type reactor or the secondary side of a generic pressurised water reactor (PWR) type reactor. Among the four actual tests performed in PERSEO, Test 7 was chosen for the benchmark activity for its completeness. The test is at full pressure (70 bar) and aims to verify the system stability with different water pool levels and the long-term cooling capability of the system.
Taking into account previous code applications on PERSEO tests, the main benchmark objective is to evaluate the capability of the adopted codes in the prediction of the heat transfer in a full-scale heat exchanger submerged in a liquid pool (both tube side and pool side). Moreover, it analysed the capability of the codes to evaluate the coupling processes between the two pools in the PERSEO system, connected in a two-phase natural circulation circuit, and the phenomena occurring in the pools themselves (e.g. thermal stratification, natural convection). The goal of the benchmark is also to characterise the user effect to predict the heat exchanger heat transfer (e.g. tuning of the heat transfer hydraulic diameter, tuning of fouling factors multiplier) and to test the code-user nodalisation strategies to model the phenomena taking place in large pools (e.g. 1D nodalisation, 2D fictitious nodalisation, 3D nodalisation if available in the adopted code).