Context: During the course of a severe accident in a Pressurized Water Reactor, large amounts of hydrogen could be generated and released into the containment. The integrity of the containment could be hazarded by certain hydrogen combustion modes. As boundaries between the different combustion modes are characterized by narrow gas concentration bandwidths, gas distribution calculations are needed to generate the initial conditions of a subsequent combustion process.

Objective: The objectives of the proposed internship is to evaluate and improve the capacity of the CEA in-house CFD code TrioCFD to make predictions of pressure-, temperature- and gas concentration distribution inside containments under severe accident conditions. Such predictions are relevant for the assessment of the conception of existing and future containments. TrioCFD has already shown its capacity to correctly predict the formation and erosion of helium stratification layers. Simple models to treat steam condensation in the volume (fog formation) and on cooled walls will be added as source terms to TrioCFD. This simplified modelling will be tested on the separate effect CONAN experiment of the University of Pisa and on the integral MISTRA experiment used in the international standard problem ISP47.

http://www-trio-u.cea.fr/ is the CFD reference code of the Nuclear Energy Division of CEA for unsteady, low Mach number, turbulent flows. The code, developed at CEA-Saclay, is especially designed for industrial CFD calculations on structured (parallelepipeds) and non-structured (tetrahedrons) grids of several hundreds of millions of elements. The object oriented, intrinsically parallel code structure is realized in C++. The user has the choice between various discretization methods and can combine several appropriate physical models including different methods to treat turbulence. The code is used on a daily basis for safety studies on massively parallel computers by using up to 10000 processor cores.