A STUDY ON RISK ANALYSIS FOR LOADING AND UN-LOADING ACCIDENT

Low Level Waste packages are transported from each Japanese nuclear power plants to Rok:kasho-Mura by exclusive ship. These packages are contained in half-height 5 ton containers. The handling system for loading and unloading containers is composed of the 25 ton crane, the cell-guide system and transport trucks. These systems are mostly automated and under computer control. By design, the whole handling system should be highly protected from any accident. However unknown causes for accidents might be concealed in this handling system, because of complicated system interaction between computer control and human operation. The representative 25 ton bridge type crane was analyzed in this assessment As the first step, causes of drop accidents were analyzed using design drawing of the crane and its system operation flow chart as inputs to the analysis. After analysis the protection methods were reviewed, and where necessary, revised in each step of accident cause. Those results were rearranged by fault trees for each cause. To provide quantitative details of operational interactions. crane operators and safety supervisors were consulted. Based on their experience, a method to determine probabilities of basic events was tentatively adopted. According to this assessment, each protection method was clarified and some weak points of the loading and un-loading process were able to be identified. Figure 1 shows schematically the sequential steps in the method. As a result of this assessment, the PSA method (including fault trees, etc.) was found to be adaptable for the loading and un-loading process (i.e. handling system) and to be effective in understanding the system characteristics. Further, using this PSA analysis method allows transport companies to review protection methods with \"Cost & Benefit\" analysis concepts.