Abstract
A large amount of Hydrogen gas is expected to be released within the dry containment of a pressurized water reactor (PWR), shortly after the hypothetical beginning of a severe accident leading to the melting of the core. According to local gas concentrations, the gaseous mixture of hydrogen, air and steam can reach the flammability limit, threatening the containment integrity. In order to prevent mechanical loads resulting from a possible conflagration of the gas mixture, French and German reactor containments are equipped with passive autocatalytic recombiners (PARs) which preventively oxidize hydrogen for concentrations lower than that of the flammability limit. The objective of the paper is to present numerical assessments of the recombiner models implemented in CFD solvers NEPTUNE_CFD and Code_Saturne. Under the EDF/EPRI agreement, CEA has been committed to perform 42 tests of PARs. The experimental program named KALI‐H2, consists checking the performance and behaviour of PAR. Unrealistic values for the gas temperature are calculated if the conjugate heat transfer and the wall steam condensation are not taken into account. The combined effects of these models give a good agreement between computational results and experimental data.
Highlights
During a design-basis accident (DBA) or a severe accident (SA) in a nuclear power plant, certain chemical reactions may produce hydrogen, in such a way that hydrogen and oxygen volumetric concentrations may exceed the lower flammability limits (LFLs)
Thanks to a code–to-experiment benchmark based on the COPAIN and TOSQAN facilities (Malet, 2008), we successfully evaluated the ability of the code to reproduce the vapor condensation at wall, atmosphere mixing and stratification in a vessel
These phenomena are of relevant interest in many industrial applications, especially regarding nuclear power plant containment at accident conditions
Summary
During a design-basis accident (DBA) or a severe accident (SA) in a nuclear power plant, certain chemical reactions may produce hydrogen (hydrogen is produced from the oxidation of zirconium sheaths and structures of fuel elements during the phase of core degradation), in such a way that hydrogen and oxygen volumetric concentrations may exceed the lower flammability limits (LFLs). Catalytic recombiners can start up with hydrogen fraction equal to about 2 % This paper focuses on numerical assessments of PAR’s modeling implemented in CFD solver Code_Saturne and CMFD solver NEPTUNE_CFD (Braillard,1999), (Bachellerie, 2003), (Avakian, 1999), (Fineschi, 1996), Deng, 2008), (Kudriakov, 2006). The used turbulence model for containment applications is the standard k-epsilon one, supplemented by wall log laws for taking into account the turbulent friction and gaseous heat transfer between the fluid and the surrounding structures
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