The aim of this paper is to present the status of the CFD simulation developments carried out by the French “Institute for Radiological Protection and Nuclear Safety” (IRSN). This paper concerns especially the accidental fires in a well-confined and mechanical ventilated room in the framework of fire safety in nuclear power plants (NPP) and reprocessing plants (NRP). A high confinement level to prevent the environment from possible release of radioactive particles as fire consequences characterizes this type of nuclear compartments. To investigate these special fire rooms, an experimental program FLIP has been performed by IRSN, in collaboration with COGEMA, in a fire test cell facility of about 400 m3 connected to an industrial-like ventilation network. Located against the middle of a wall of the test cell, many square pool fires of ethanol (0.4 and 1 m²) and TBP/TPH (ranged from 0.4 to 3.2 m² in area) have been studied (/AUD 99, TOU 00, AUD 00, PRE 00/) and provided a significant experimental database for computer code validation. In this paper, a CFD simulation of one FLIP fire test is carried out by the computer code named ISIS and developed by IRSN based on a field modeling approach (/FER 02, POI 01/). The Favre-averaged continuity, species conservation, momentum and energy equations are solved for a low Mach number turbulent reacting multi-component flow. The low Mach number model is coupled with Bernoulli equations to simulate the industrial ventilation network and allow us to calculate the pressure evolution in the fire enclosure. In addition to the transport equations, the k-turbulent model is employed with additional source terms to account for the buoyancy effects. The log-law is adopted as wall functions. The combustion process is handled via the EDC model or the PDF model, both derived from the assumption of an infinitely fast chemistry. Concerning the radiative heat transfer, the Marstein approach or the diffusive flux model can be used. The comparison between the numerical results and the experimental data from the FLIP fire test (temperatures, pressure) shows a satisfactory agreement on the whole. Especially, the thermal stratification in the compartment is quite well reproduced by the computer code. Moreover, the analysis of temperature and velocity fields permits a better understanding of the fire consequences in the well-confined and forced ventilated compartments.
1 : IRSN
2 : ASSYSTEM