hydrogen mobilization by passive autocatalytic recombiners

International audienceDuring the course of a severe accident in a Pressurized Water Reactor (PWR), large amount of hydrogen can be released into the containment. As a consequence, the integrity of this third barrier can be compromised by severe combustion events. The strength of hydrogen combustion processes strongly depends on range of gas concentration and thermodynamic variables. It is therefore imperative that accurate gas distribution and mixing experiments and related calculations related to severe accident are conducted. The recent Fukushima accident has recalled that such a massive hydrogen explosions still represents an open safety issues. Consequently, stress tests have been performed and a number of projects have been launched to address identified safety gaps. The MITHYGENE project funded by the French Research Agency ANR and industrial partners (EDF, AREVA and Air Liquide) aimes at improving knowledge on hydrogen risk and related safety management during a se! vere accident. In this project, the MISTRA facility operated by CEA is used to investigate the capability of a natural convection flow, induced by Passive Autocatalytic Recombiners (PAR) operation, to remobilize an accumulation of light gas trapped below. This important safety issue for designers and safety engineers was identified in several previous projects such as SARNET and SETH-II. As a first step, pre-test calculations with CFD models were performed to design the tests. In the second step, different series of tests were realized in the MISTRA facility, and finally, post-test calculations were conducted to improve the modeling. This experimental and analytical work demonstrates the limited effect on the destratification and the importance for designers to install the PARs also in the lower part of the nuclear reactor containment