The leak tightness of nuclear power plant containments under accidental conditions is a crucial topic in the safety discussion about the operating lives of nuclear power plants. The self-healing potential of cracks in concrete thereby might contribute an important share to avoid possible contamination of the environment. Small scale flow-through experimetns with air and steam, conducted under variable pressure and temperature conditions at the MPA Karlsruhe shall gap the bridge between previously performed large scale leakage tests and the sole description of the relevant and already well known chemical and physical processes. The tests were conducted on specimens of cementitious constructions materials, i.e. concrete and typical concrete ingredients (sandstone, limestone, granite) to separate possible effects by the material. Experimental conditions were chosen according to realistic temperature and pressure conditions of an accidental scenario. The experimental setup shall first of all measure the amount of flow through the crack and subsequently its reduction accompanying the different crack healing processes. For the assessment ... mehrand quantification of the mineralogical crack healing processes, the crack surfaces were investigated by ESEM, µ-RFA and microscope. Within this paper, the first results were summarized and compared with results from the large scale experiments. A detailed description of the experimental setup is given as well.