Evaluation of the pressure loads generated by hydrogen explosion in auxiliary buildings of a nuclear power plant

A. Bleyer, A. Bentaïb, J. Dupas, C. Caroli, B. Chaumont, J. Rivière,
11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11),
Avignon, 2-6 octobre 2005,
Rapport DSR 83

A hypothetical hydrogen leak in an auxiliary building of a nuclear power plant (NPP) would raise an explosion hazard. A local ignition of the combustible mixture would give rise to a slow flame, rapidly accelerated by obstacles. This flame acceleration could be responsible for high-pressure loads that could damage the auxiliary building and destroy safety equipment.

In this paper an example is given of a complete analysis of this risk using advanced CFD tools and structural analysis computer codes. The hydrogen distribution is first evaluated on the basis of multidimensional computations of viscous turbulent flows. The combustion-induced loads, based on the above computed hydrogen distributions, are then evaluated by multidimensional combustion calculations using a simplified combustion model. These loads have also been evaluated for bounding conditions corresponding to stoichiometric hydrogen-air mixtures. For each scenario, the impact of the ignition location and ignition time has been investigated. These pressure loads have been then used to investigate the occurrence of a mechanical failure of the tanks located inside these buildings and whose damage may constitute a potential environmental risk.

The hydrogen dispersion and explosion computations have been carried out using the TONUS code, which is developed by CEA on behalf of IRSN (Paillere et al, 1997). The used dispersion model is based on a finite element solver. The explosion is simulated by a structured finite volumes EULER equation solver together with the CREBCOM (Criteria and Experimentally Based Combustion Model) combustion model, which simulates the hydrogen/air turbulent flame propagation, taking into account a 3D complex geometry and reactant concentration gradients. The EUROPLEXUS (Casadei, 2003) code has been used to perform 3D mechanical calculations.