Research on hydrogen risk mitigation resulting from hypothetical severe accident - Major results from the 4(th) framework programme and actual research in the 5(th) framework programme

The evolution and release of hydrogen in the course of hypothetical severe accidents in light water reactors is seen to be a potential cause of early containment failure due to possible follow-on reactions in the containment. The cause of concern is the volume of hydrogen produced in the zirconium-water interaction of fuel cladding tubes and structural materials in the reactor core. As a result of deflagration processes and transfer processes, respectively, from deflagration to detonation, this hydrogen can cause local pressure peaks which exceed the containment design basis. For this reason, the phenomena of hydrogen generation, distribution, and reactions have been studied worldwide for a number of decades, and concepts are being developed for controlling this situation. In Germany and in other European countries, the concepts pursued comprise the use of recombiners and ignition devices Or a combination of both systems. These systems are being planned for backfitting into existing nuclear power plants and for installation in the European Pressurized Water Reactor (EPR) under development. Since the mid-nineties, several research programs have been devoted to this topic within the framework of joint European reactor safety research. Activities are concentrated on hydrogen generation, hydrogen distribution, the effectiveness of recombiners as well as turbulent combustion and the transition from deflagration to detonation, among others.