[en] As an example for a low power research reactor a probabilistic safety assessment is undertaken for the 250 kW TRIGA Mark-II reactor Vienna. A major area of interest is the identification of different accident causes, the description of the following accident sequences and the influence of uncertainties. The usual technique in PSA studies is the selection of 'Accident Initiating Events' which are considered to be relevant for the reactor under investigation. For the TRIGA reactor Vienna with its low power density and natural convection cooling core melt-down is impossible. Therefore, it is more advisable to use a single large fault tree (Master Logic Diagram, MLD) which displays the pathway leading to an undesired, predefined event. In the present study this undesired top event of the MLD is a radiation exposure of persons (either occupational or public) and about 15 pathways leading to this event have been identified. The determination of the minimal cut sets of the various fault trees is either accomplished by hand in simple cases or with the help of the computer code ORCHARD in more complicated cases. Within the scope of the quantification of the PSA-structures the following topics are investigated: - failure data collection and preparation; - human reliability analysis; - uncertainty analysis; - sensitivity analysis. Particularly, the examination of the influence of uncertainties is a major area of interest. With the help of the computer code SAMPLE the most significant method for the calculation of uncertainty propagation is studied: the 'Monte Carlo'-method. (author)