Validation of the lumped parameter code COCOSYS against large‐scale OECD PRISME 2 fire experiments

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SummaryFire safety analysis is a major issue for nuclear power plants (NPPs) in the context of deterministic safety assessments as well as of probabilistic safety analyses. Oil reservoirs and cables represent major fire loads. Therefore, simulations of oil and cable fires are of interest for quantifying the risk of such internal hazards in NPPs. To investigate the applicability of lumped parameter (LP) modelling, validations against fire experiments are required. In this way, results obtained with the LP code COCOSYS for simulations of oil and cable fire experiments conducted in the OECD PRISME 2 Project are presented. The PRISME 2 VSP (vertical smoke propagation) tests involving oil fires in a confined and mechanically ventilated facility were used to assess the ability of the LP code to simulate smoke propagation through a horizontal opening from the fire compartment to a compartment on top of it. As it was already identified in the “International Collaborative Fire Modelling Project (ICFMP),” this type of opening might cause problems in fire simulations, particularly for zone or LP fire models. In these simulations, attention has been paid to the coupling between the fire and the surrounding environment due to the decrease of oxygen concentration. Furthermore, different cable materials have been tested in the PRISME 2 CORE (completing and repeating) test campaign. By simulating the CFS‐3 (cable fire spreading) test with confined underventilated conditions, the applicability of the COCOSYS cable fire model with input parameters deduced from open atmosphere fire tests (CORE‐2) was analysed. Results show that the applicability of a LP fire model to predict the pyrolysis rate is partly limited for both oil and cable fires, in confined environment. However, simulations with prescribed pyrolysis rates show encouraging results in good agreement with the experimental data and underline the capability of the LP code COCOSYS to simulate the interaction between the thermal hydraulics inside compartments and the fire source.