SARNET hydrogen deflagration benchmarks: Main outcomes and conclusions A. Bentaib a,⇑ , A. Bleyer a , N. Meynet a , N. Chaumeix b , B. Schramm c , M. Höhne c , P. Kostka d , M. Movahed e , S. Worapittayaporn e , T. Brähler f , H. Seok-Kang g , M. Povilaitis h , I. Kljenak i , P. Sathiah j a Institut de Radioprotection et de Sûreté Nucléaire, 92269 Fontenay-aux-Roses, France b Institut ICARE, 1C route de la recherche scientifique, Orléans, France c GRS, Gesellschaft für Anlagen- und Reaktorsicherheit (GRS)mbH, Germany d NUBIKI, Institute for Electric Power Research, Hungary e AREVA, AREVA NP GmbH, 91058 Erlangen, Germany f RUB, Ruhr-University Bochum, Germany g KAERI, Korea Atomic Energy Research Institute, Republic of Korea h Laboratory of Nuclear Installation Safety Lithuanian Energy Institute Breslaujos g. 3, Kaunas, Lithuania i Jozef Stephan Institute, Slovenia j Nuclear Research and Consultancy Group, 1755 Le Petten, Netherlands article info Article history: Received 6 January 2014 Accepted 7 July 2014 Available online 6 September 2014 Keywords: Combustion CFD LP Diluents Hydrogen Turbulence abstract In case of a core melt-down accident in a light water nuclear reactor, hydrogen is produced during reactor core degradation and released into the reactor building. This subsequently creates a combustion hazard. A local ignition of the combustible mixture may generate standing flames or initially slow propagating flames. Depending on geometry, mixture composition and turbulence level, the flame can accelerate or be quenched after a certain distance. The loads generated by the combustion process (increase of the con- tainment atmosphere pressure and temperature) may threaten the integrity of the containment building and of internal walls and equipment. Turbulent deflagration flames may generate high pressure pulses, temperature peaks, shock waves and large pressure gradients which could severely damage specific con- tainment components, internal walls and/or safety equipment. The evaluation of such loads requires val- idated codes which can be used with a high level of confidence. Currently, turbulence and steam effect on flame acceleration, flame deceleration and flame quenching mechanisms are not well reproduced by combustion models usually implemented in safety tools and fur- ther model enhancement and validation are still needed. For this purpose, two hydrogen deflagration benchmark exercises have been organised in the framework of the SARNET network. The first benchmark was focused on turbulence effect on flame propagation. For this purpose, three tests performed in the ENACCEF facility were considered. They concern vertical flame propagation in an initially homogenous mixture with 13 vol.% hydrogen content and different geometrical configurations. Three blockage ratios of 0, 0.33 and 0.6 were considered to generate different levels of turbulence. The second benchmark objective was the investigation of the diluting effect on flame propagation. Thus, three tests performed in the ENACCEF facility using the same blockage ratio of 0.63 and three different initial gas compositions (with 10, 20 and 30 vol.% diluents) have been considered. Since ENACCEF runs at ambient temperature, a surrogate to steam was used consisting of a mixture of 0.6He + 0.4CO 2 on molar basis. This paper aims to present the benchmarks conclusions regarding the ability of LP and CFD combustion models to predict the effect of turbulence and diluent on flame propagation. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction In case of a hypothetic severe accident in a light water nuclear reactor, hydrogen would be produced during reactor core degrada- tion and released into the reactor building. This could subsequently cause a combustion hazard. A local ignition of the combustible mixture may generate standing flames or initially slow propagat- ing flames. Depending on geometry, mixture composition and tur- bulence level, the flame can accelerate or be quenched after a certain distance. The loads generated by turbulent deflagration flames may generate high pressure pulse, temperature peaks, http://dx.doi.org/10.1016/j.anucene.2014.07.012 0306-4549/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +33 1 58359854; fax: +33 1 46572274. E-mail address: ahmed.bentaib@irsn.fr (A. Bentaib). Annals of Nuclear Energy 74 (2014) 143–152 Contents lists available at ScienceDirect Annals of Nuclear Energy journal homepage: www.elsevier.com/locate/anucene