CFD Investigation of Hydrogen Combustion in a Simplified EPR Containment with CFX and Reacflow

In case of a severe nuclear accident, large amounts of hydrogen could be generated by a metal-steam chemical reaction during the core melt down. The containment integrity can be jeopardised by the over-pressures that are generated by hydrogen explosions with the potential consequence of radioactive material release into the environment. The prediction of over-pressures and temperatures during hydrogen combustion is an essential stage of the safety analysis. Due to the extremely high costs of experiments, the use of Computational Fluid Dynamics (CFD) modelling for safety purposes has been constantly increased within the nuclear community. The investigations presented in this paper are a continuation of the numerical studies of validation and benchmarking that were carried out in the European co-sponsored project HYCOM (Integral Large Scale Experiments on Hydrogen Combustion for Severe Accident Code Validation; 2001-2003). In the present work, numerical simulations of hydrogen deflagrations within a simplified, real-scale EPR (European Pressure Reactor) containment have been performed with two CFD codes, CFX4 and REACFLOW. CFX4 is a well-known commercial code that has been employed at GRS for several years for different applications in the context of severe accidents. REACFLOW is an in-house code that has been developed at JRC in order to perform numerical simulations of reacting flows. The analysis has been focused not only on overpressure peaks and pressure oscillations, but also on pressure differences between the two sides of the same wall between steam generator rooms and pump rooms. Since the internal geometrical layout affects the behaviour of hydrogen combustion, different geometrical configurations have been considered in term of presence of vents between internal compartments and in term of vents number, size and position. Single and multiple ignition points have also been taken into account. The paper describes the main results of the investigation and it is a demonstration of how CFD modelling can provide significant indications for real-scale safety applications within the limits of uncertainty of the accident scenario.

HEITSCH Matthias;  WILKENING Heinz; 

BARALDI Daniele; 

2005-11-30

CEA

JRC30694