CATHARE calculation of the tests conducted on the ELSMOR passive heat removal system

• ELSMOR project supported LW-SMR licensing via passive heat removal experiments. • Tests on this facility were modelled and simulated using the CATHARE 3 code. • Exchanged power predicted within ±10 %, with up to 20 % error in some cases. • Safety condenser strongly affects behavior; compact steam generator influence is limited. • CATHARE 3 underestimates the safety condenser outlet temperature and overestimates SC pressure. As part of the ELSMOR (Toward European Licensing of Small Modular Reactors) project, an experimental facility has been set up at SIET (Piacenza, Italy) to test a passive heat removal system. Such a passive system operates in natural circulation, with three different circuits: a primary circuit (PC, the heat source), a secondary circuit (SC, self-pressurised) and a tertiary circuit (the heat sink, represented by a pool). The primary and the secondary circuits are thermally coupled to a plate-type Compact Steam Generator (CSG), while the secondary and the tertiary circuits are coupled to an in-pool condenser. An experimental campaign has been carried out to investigate the effect of different parameters on the passive system behavior, through different types of tests (e.g. secondary side filling ratio (FR) or non-condensable gas (NC) concentration, primary system temperature, pool level, etc.). These experimental tests are modelled with the CATHARE 3 code (French system calculation code) and the calculation results are compared with the experimental data. The CATHARE 3 code predicts good tendencies for the tests on the main parameters of the facility (exchanged power, secondary circuit pressure, condenser outlet temperature). For the majority of the tests, the discrepancy between experimental and calculation results for the exchanged power in the CSG is below 10 %: for high FR in the SC, the CATHARE 3 code predicts the exchanged power well, while for low FR the power is overestimated. Sensitivity calculations showed that the condenser has the main influence on the facility behavior (the CSG has a limited influence); in particular, the correlations in the secondary side of the condenser have a significant influence on the exchanged power, while the correlations in the tertiary side have a small influence; thus, the tertiary modelling has a small influence on the calculation results. For all tests, the CATHARE 3 code underestimates the SACO outlet temperature and overestimates the pressure in the SC. Nonetheless, the presence of experimental uncertainties, particularly related to uncharacterized head losses and two-phase flow conditions, prevents drawing fully conclusive statements about the model accuracy.