The Reactor Engineering research programme includes basic and applied research in nuclear energy, engineering and safety. Phenomena that occur during transients, incidents and severe accidents in nuclear power plants are being investigated. Appart from contributing to the improvement of nuclear safety, research results are applicable to a wide range of industrial processes. In the field of thermal-hydraulic safety research, the following basic phenomena that occur during design-basis accidents in light-water-reactor nuclear power plants are being investigated: heat transfer in single-phase and two-phase turbulent flow, subcooled nucleate boiling flow in vertical channels, as well as single-phase and two-phase water-hammer phenomena in piping systems. Basic phenomena which are specific to severe accidents are also being investigated: steam explosions due to interaction between coolant and molten reactor core, atmosphere mixing and stratification in the containment, steam condensation in the presence of non-condensable gases and aerosol behavior (transport, condensation and settling) in the containment. In addition, both design-basis and severe accidents are being modeled on integral scales using system computer codes. In the field of structural safety research, new models are being developed to allow prediction of micro-damages and the study of their influence on the macroscopic behavior of materials. The investigations include simulations of initiation and growth of intergranular cracks in the random grain structure. In the field of probabilistic safety assessment (PSA), new methods are being developed by including time as an additional dimension. PSA is integrated with optimization methods, such as simulated annealing. The influence of human factor on the reliability of complex technological systems is also being investigated.