During accidental situations, large quantities of hydrogen are generated and released due to metal-water reaction. Eventual stratification formed in the top region of containment and locally high concentration threatens the integrity of nuclear power plants. The stratification of hydrogen may be eroded by several measures, such as air jet, spray, ventilation. So far, several activities have been carried out on the hydrogen stratification’s break-up study. The well-known OECD/SETH-2 project used PANDA and MISTRA test facilities to study this phenomenon with variable test conditions. These test cases are also wildly used to validate the computational fluid dynamics (CFD) codes.

The large-scale containment test facility – COntainment Thermal-hydraulics and Hydrogen Distribution (COTHYD) was designed and constructed at CGN to study the containment thermal hydraulics behavior and hydrogen risk in PWR during severe accidents. A series of tests including helium and air stratification, helium and air stratification eroded by air jet, as well as steam dispersion and condensation are planned to be performed on this test facility. The objective is to set up high quality database for code validation and physical phenomena research.

During the test cases preparation, the relevant tests carried out since 2000 in MISTRA, TOSQAN, THAI, PANDA were collected to give the reference for the cases design in COTHYD. For the tests of stratification’s break-up on COTHYD, helium is discharged from top and it accumulates at the top region of containment. On the preparation stage, Code_Saturne was used to define the test scenario and predict helium distribution. Both dead volume and open volume (with ventilation) are modeled to investigate helium stratification formation and helium-rich layer concentration evolution. These results will be used as test matrix configurations. Code_Saturne, EDF in-house open-source software, has been used in the simulation of hydrogen dispersion. In 2015, B. Hou presented their work on the simulation of the break-up phenomenon of helium stratification by air (ST1_7 and ST1_10 test cases of OECD/SETH-2 project) (Hou et al., 2015) [1]. Simulation results demonstrated that Code_Saturne can well predict and simulate this phenomenon. This software is, as a consequence, used as the case design and validation tools in the pre/post experiment steps.

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