Benchmark of the Heiss Dampf Reaktor E11.2 containment hydrogen-mixing experiment using the MAAP4 code

The Modular Accident Analysis Program Version 4 (MAAP4) is an integrated se vere accident analysis code that integrates a large number of phenomena and models into a single plant simulation. MAAP4 was used to predict the conta inment response to a simulated small-break loss-of-coolant accident steam b lowdown followed by the release of a hydrogen/helium gas mixture (test E11. 2) in the decommissioned German Heiss Dampf Reaktor facility. The test also incorporated external spray cooling of the steel dome near the end of the transient. In MAAP4, 29 nodes and 44 flow junctions were used to model the highly compartmentalized containment. The MAAP4 prediction of the containme nt pressure and gas temperature over the duration of the transient and the transient distribution of hydrogen/helium in, the containment compartments are compared with experimental results. MAAP4 overpredicts the pressure and correctly predicts the thermal and hydrogen stratification that was observ ed in the E11.2 test.