Selection of bounding events for ITER safety analysis

In analyses of postulated accident scenarios as part of the safety assessment of ITER, a systematic approach to the selection of events to be studied provides justification for their choice and confidence that the set is comprehensive. Systematic accident identification performed for ITER, mainly using failure modes and effects analysis (FMEA), has provided an extensive catalogue of postulated initiating events (PIEs). This information is now used in the PIE potential impacts table (PIE-PIT), which displays the links from PIEs to a limited set of plant states derived from a functional view of the ITER confinement scheme. A total of twelve plant states represent all significant conditions in which some release to the environment is possible in principle, and from these a set of seven is chosen as clearly bounding the potential consequences of the entire set. This leads to the selection of just seven scenarios as a bounding event set for the ITER tokamak. There is a direct correspondence between these bounding events and events studied in earlier ITER safety analyses. This set of seven bounding events will provide a sound basis for further safety analyses to be performed as the ITER project moves into a licensing stage.