CFD Simulation of PANDA and MISTRA Cooler Tests of ERCOSAM-SAMARA Project

Abstract

The ERCOSAM and SAMARA projects (EURATOM (EU) and ROSATOM (Russia)) include a set of multi-stage experiments carried out at different thermal-hydraulics facilities (TOSQAN, MISTRA, PANDA, SPOT). The tests sequences are aimed at investigating hydrogen concentration build-up and stratification during a postulated severe accident and the effect of the activation of Severe Accident Management systems (SAMs), e.g. sprays, coolers and passive auto-catalytic recombiners. Each test includes four phases, of which the first three phases simulate the establishment of severe accident conditions in NPP containment (injection of steam and helium (simulator of hydrogen), stratification of the gas mixture). During the fourth phase of the experiment one of the SAMs simulators is activated. All experiments were simulated at Nuclear Safety Institute of the Russian Academy of Science (IBRAE RAN) with FLUENT and, partially, OpenFOAM codes. In this paper the tests with coolers carried out on PANDA and MISTRA facilities are considered. Their simulations required development of a set of models of volumetric and near-wall condensation phenomena. The models were validated vs. already known tests and vs. integrated experiments of ERCOSAM-SAMARA projects. A brief description of the models and the used CFD methods is provided. Then the results of simulations of the four phases of the tests are presented. Some peculiarities of gas motion and helium distribution obtained in the experiments as well as in their simulations are analyzed. These phenomena concern steam condensation and helium redistribution by convective flows due to the cooler activation in the installation. Local ‘pockets’ of helium are formed with a molar fraction larger than the maximum achieved at the first three phases of the experiments. The accounting of initial and boundary conditions along with calibration of the models provided as a whole a good agreement between calculations and experimental data on transient behavior of gas composition in the facility at the first three phases and at the final fourth phase.