Assessment of Severe Accident Management Measure Efficiency with MELCOR 1.8.6 Code

The basic input data for the MELCOR testing comes from the VVER-1000 input model developed in the NRI. The main identified SA measures to be tested are focused on the prevention of high energetic phenomena (HPME and DCH), hydrogen removal using passive autocatalytic recombiners, in-vessel retention using the external flooding of reactor cavity, and passive system for heat removal from containment. Simulation of the fast primary circuit depressurization was vary simple and generally without any unexpected results. Its simulation was done with one additional flow paths with appropriate control using control functions. Methodology for the simulation of hydrogen removal system (HRS) was more complicated, because mass and energy sources into the containment were simulated using the whole plant input model, which includes relatively simple model of the containment. The study of the HRS itself is done with very detailed stand-alone model of the containment. Simulation of the in-vessel retention requested new modeling of reactor cavity with modeling of flow baffle. The MELCOR code was able to simulate this measure