Simulation of Hydrogen Deflagrations with the Lumped Parameter Code COCOSYS

Abstract In case of a postulated loss-of-coolant accident (LOCA) in a light water reactor, core degradation might occur if emergency measures fail. During this process a large amount of hydrogen might be generated by the oxidation of zirconium in the fuel rod cladding with steam. If the hydrogen leaks into the containment of a pressurized water reactor or the reactor building of a boiling water reactor and if the design concept of passive autocatalytic recombining is not adequate or fails due to adverse atmospheric conditions, it might form a combustible mixture with air. In case of ignition, pressure peaks can occur that are relevant for the integrity of the containment or the reactor building and safety systems. In the past 20 years 45 hydrogen deflagration tests (HD tests) have been performed in the THAI/THAI+ test facility with a free volume of 60 to 80 m3 which is operated by Becker Technologies GmbH in Germany. The lumped parameter code COCOSYS V3.0 (Containment Code System) which is part of the software package AC2 2019 developed by Gesellschaft fur Anlagen-und Reaktorsicherheit (GRS) gGmbH offers the models FRONT and COMB for the simulation of hydrogen deflagrations in the containment or reactor building of a nuclear power plant (NPP). COCOSYS simulations of select THAI+ HD tests are shown, and model development potential is deduced.