Spray systems and hydrogen recombiners are emergency systems designed for preserving the integrity of the containment that constitutes the last barrier to the release of fission products into the environment in case of a severe accident in a Light Water Reactor. Evaluation of the spray efficiency in containment depressurization and removal of fission products relies on the modelling of various phenomena, namely the droplets kinetic and thermal relaxation, gravitational coagulation, the aerosol particles inertial capture and interception, and the gaseous species mass transfer and chemical transformation. A model describing these phenomena has been developed in the ASTEC integral code, and qualified against the CSE and CARAIDAS experiments. New modelling features have been developed in order to match the experimental data. Unmitigated hydrogen combustion after prolonged core dryout could lead to containment failure or damage equipment, impeding core recovery. Passive autocatalytic recombiners can limit local hydrogen accumulation. In ASTEC, detailed and simple hydrogen recombination models are available. The recombination laws were fitted on SIEMENS and AECL recombiners and qualified on H2PAR experiments and then implemented into the code. A simulation with ASTEC V1 of such events in the containment of a 900 MWe PWR under severe accident conditions is presented.