Effect of FDS uncertainty in fire simulations of nuclear power plants under different ventilation conditions

Fire Dynamics Simulator (FDS) is a well-known fire computer model, which has been widely applied for different scenarios. In particular, several standards and guidelines support its use in fire safety engineering approaches in nuclear plants. Although the uncertainty of the FDS model has been analysed and collected in literature, the influence of each input parameter has not yet been fully addressed. Some of these previous contributions were based on the Benchmark Exercise No. 3 of the International Collaborative Fire Model Project (NUREG 6905). Moreover, the Best Practice Guidelines of NEA/CSNI/R (2014)11 were used as the reference to analyse the influence of the boundary conditions on simulation results. This work aims to study the impact of selected key fire dynamics parameters on the simulations of that scenario, updating previous findings. Since this fire scenario involves three horizontal cable trays and one vertical cable tray, it is of special interest for nuclear power plants. Moreover, it is relevant to analyse the influence of input parameters on cable ignition. A sensitivity analysis was conducted, to evaluate the most important parameters for the selected scenario, focussing on ventilation and the thermal properties of the cables such as conductivity, specific heat, density, emissivity. The results show the influence of each parameter in the surface temperature and heat flux in the different cable trays. Consequently, this enables the authors to formulate some recommendations for defining fire scenarios when applying fire safety engineering principles in nuclear power plants.