Selection of DBEs for ITER EDA 1998 final design by GEMSAFE methodology

Abstract General Methodology of Safety Analysis and Evaluation for Fusion Energy Systems (GEMFASE) has been applied to the International Thermonuclear Experimental Reactor (ITER) design in the final stage of Engineering Design Activities (EDA) by the end of July 1998 to select design basis events (DBEs) and to identify related safety features as well as requirements to ensure its safety. We have classified DBEs into three categories considering their occurrence probabilities and expected scales of their consequences. By the GEMSAFE methodology applied to the ITER final design, we have selected 21 DBEs, eight in category I, eight in category II, and five in Category III. Here, we have focused on the following characteristics of the final design of ITER EDA of 1998. The amount of mobile radioactive materials, or RI sources, in the front-end permeator of the fuel gas purification system was largely increased to 70 g, cf. 15 g in an earlier EDA design. Though it does not change the class of the related DBE, the consequence by the related abnormal event would be more severe. The inventories of tritium in the impurity detritiation system, and that in surge tanks were not decreased, namely, still exceeding the limit of the class-1 RI source (i.e., 105 Ci). As for the radioactive dusts, their inventory increased. However, we need not modify the DBEs so long as we categorize the radioactive dust as immobile RI source. The mobility of the dust is a matter of further detailed examination. If we would find the dust is a mobile-RI-source category, it might challenge the baseline to fit the equi-risk curve. Further discussions are necessary for the characteristics of the dusts, and the safety measures to reduce the inventory during operations.