Risk analysis applied to the ultimate storage of radioactive waste

The suitability of an ultimate storage facility for radioactive waste cannot be shown experimentally, the periods involved being too long. Therefore, experimental storage in each case can only demonstrate the usability of different concepts and engineering appliances. This is why risk analysis is of special importance for the system ultimate storage because the safety or the residual risk of a special ultimate storage facility has to be shown from it. The quantitative risk analysis starts with the definition: risk is equal to the probability of occurrence multiplied with the potential damage. By applying the fault tree analysis, the sequence of events can be subdivided into single events which may lead to the undesirable top event release of activity into the biosphere. Many events of this kind are developing slowly, even within a period of millions of years; thus it is the principle aim to determine the probabilities of occurrence and, if possible, their time dependence. After assessing the risk it is then possible to make a comparison with a predetermined acceptable risk which should answer the question whether the chosen concept in a sepcified geological environment will not become an unsupportable risk without benefit also for future generations. (orig.)