Comparisons between HDR-H2-distribution experiments E11.2 and E11.4

The combination of issues important for the physical phenomena governing the H2-mixing and distribution mechanisms in post-severe accident containment atmospheres, namely: large scale of the experimental facility, high H2-release rates, superheated steam injection into the containment, multi-compartment geometry with sufficiently large dome volume representation, representative internal concrete and metal structures and surfaces, energy transfer across the containment steel shell into a very high annular ring space of 50 m height, multiple steam and H2-injection phases, different axial positions for H2-releases, examination of the efficiency of H2-mitigating features including external dome, and spray as well as venting, has not been investigated yet in any experimental facility worldwide. The HDR with its subsystems has the features cited above. Therefore, Test Group E11 was designed and performed in 1989 to provide a first data set for severe accident containment atmospheres in close to real multi-compartment geometry. The test group consisted of the total of eight different experiments addressing a wide spectrum of H2-distribution and mitigation issues. The paper focuses upon two experiments which both cover small break scenarios and a variety of mitigating measures