After the reactor accident in Fukushima Daiichi NPP the safety of nuclear spent fuel pools became omnipresent in public perception and more focused in nuclear safety research. The detailed course of the heat and mass transfer mechanisms of spent fuel pools with fuel assemblies fully or partly covered by water are yet relatively unknown and there are missing experimental results to validate existing models. Against this backdrop, the German national joint project SINABEL that is funded by the German Federal Ministry of Education and Research investigates the thermal hydraulics of selected accident scenarios in spent fuel pools experimentally and numerically. For the experimental investigation, the integral test facility ALADIN was built up. A central electrically heated boiling water reactor (BWR) fuel element was copied in original scale and surrounded by additional heating cartridges to simulate the surrounding and to adjust nearly adiabatic boundary conditions. The unique 3-D net of instrumentation allows the observation of the cladding temperature distribution and temperature development combined with filling level measurement and video monitoring. Experiments for various scenarios of water level position were conducted at cladding temperatures up to 450 °C. The paper describes the thermal hydraulics of the heat up and the boil-off phase. This comprises the occurrence of subcooled boiling in the beginning and geysering-like instabilities arising during evaporation. A detailed analysis of the associated rewetting and cooling of the heating cartridges is done. Thus, these insights can help to fill the gap of fundamental knowledge about the thermal hydraulics of accident scenarios in order to estimate the effects on the safety of spent fuel pools. The experimental data will be used for validation and refining of numerical simulation.