Multi-step planning calculations with the GOTHIC code used for the design of complex experiments in the PANDA facility

Highlights: • Complex experiments in PANDA have been designed using planning calculations with GOTHIC. • A multi-step procedure has been developed to reproduce the main phenomena. • The experiments confirmed the main trends predicted by the planning calculations. - Abstract: The evaluation of the hydrogen risk and mitigation measures is increasingly based on the three-dimensional analyses of the distribution of gases and steam in the containment. Currently, simulations are thus carried out with advanced computational tools, including CFD codes, which require extensive validation using detailed measurements in large-scale facilities. However, since these facilities were designed for specific geometries and accident conditions, global scaling criteria are of limited use for designing new experiments addressing 3-D phenomena in different geometries and for different scenarios. Therefore, planning calculations are required to ensure that the tests are representative of expected plant conditions during hypothetical accidental transients. In this paper, a multi-step methodology (from plant to rig) for designing two types of tests in the PANDA facility within the OECD/NEA HYMERES project is illustrated. The first type of experiments addressed the interaction of flows and temperature fields produced by two PARs (Passive Autocatalytic Recombiners) at different elevations in some region of a generic containment in presence of wall condensation. The second type of experiments addressed natural circulation and gas distribution in a generic two-room geometry. The main results of the two series of experiments that were designed using the outcome of this work have been reported in two papers.