Effect of spray activation on the reactivity of the hydrogen-air-steam mixture in the containment of the European pressurized water reactor(EPR)

The justification of the EPR hydrogen mitigation and control system is essentially based on the 3D field code GASFLOW /1, 2/. The system consists of recombiners and is supported by the dedicated primary bleed system, which guarantees a large amount of steam in most scenarios. Two trains spray system of the EPR is designed to avoid failure of the containment by overpressurization, as may result from long-term steam production caused by decay heat removal from the melt. Finite volume computer code GASFLOW-II has been extended with a spray model using thermal non-equilibrium, but mechanical equilibrium for the liquid and gas phases to analyze the impact of an early actuation of the spray system on the hydrogen risk. The effect of spray on hydrogen risk has been investigated for a bounding scenario small break loss of coolant accident with delayed depressurization (SBLOCA/D) at an unfavorable moment of the high amount of accumulated hydrogen in the containment. It could be shown that activation of the spray system does not negatively interfere with hydrogen risk aspects for the above scenario. It is expected that this conclusion remains valid for other scenarios