Probabilistic safety analysis for a shaft hoisting installation

Subject of the present probabilistic safety analysis (PSA) are transport processes during the direct disposal of POLLUX-casks in a repository. Direct disposal includes surface caging, shaft hoisting and uncaging in the mine. This analysis is aimed at finding the frequencies of events which lead to an increased radiologic exposure of the personnel or the environment. Such events are directly or indirectly due to technical failure or human malactions. This paper is dealing with technical failures only. The fault tree method was used for this analysis. The events under consideration are the events on top of the respective fault tree. After determination and allocation of the necessary reliability data the fault trees have been evaluated with respect to quantity. The result is that frequency of events with a value of < 10-9 for 10,000 disposal processes which could lead to a release of radioactive material can be considered as acceptable risk. But several times per operating year operational occurrences could make it necessary to carry out activities which result in an increased radiation exposure of the personnel. Because of the limited surface dose rate of radioactive containers and possible additional shielding measures this additional radiation exposure can be kept below the applicable limits. (author)