CMFD simulation of ERCOSAM PANDA spray tests PE1 and PE2

• Successful modeling of gas mixtures and droplet flows in multicompartment system.
• For pressure, modeling of gas-wall heat transfer (and heat radiation) is important.
• Dependence of gas mixing time in spray vessel on the used nozzle may be essential.
• Penetration of helium-enriched mixture into another vessel due to spray operation.
• Effect on pressure of sump re-evaporation and gas heating (by walls) during spray.

The ERCOSAM project (together with the SAMARA project) includes a set of multi-stage experiments carried out at different thermal-hydraulics facilities (TOSQAN, MISTRA, PANDA, SPOT) and their numerical simulation. The test sequences aim to investigate hydrogen concentration build-up and stratification during a postulated severe accident as well as the effect of activation of Severe Accident Management systems (SAMs) on stratification. At the initial Phases I–III of the tests stratification of the injected light gases (steam, helium) is established, pressure increases. The models of SAMs are activated at the final Phase IV.In the paper, two spray tests PE1 and PE2 performed at PANDA facility are numerically investigated aiming for code validation (FLUENT) and better understanding of physical processes. Phases I–IV of the tests were simulated. A satisfactory agreement with the experimental results on gas component mole fractions was obtained. The reasons of obtained some discrepancies in pressure and temperature were studied in multivariate calculations and discussed in the paper. The tests PE1 and PE2 were performed with different spray nozzles and initial conditions. In simulation that resulted in different flow patterns during spray operation. The sensitivity to nozzle angle and some other input parameters was investigated. Possible factors of depressurization rate caused by spray operation were also studied. The key features observed in the experiments and obtained numerically being of interest in terms of CFD applications to NPP hydrogen safety are summarized.