Development of a potential initiator impacts table for ITER safety analyses

ITER safety studies have included the systematic identification of postulated initiating events (PIEs) that could start event sequences leading to potentially hazardous conditions. A transparent presentation is required to show the potential impact that each PIE may have on the plant. The PIE-potential impacts table (PIE–PIT) has been developed as an approach to this. An important aspect of the development is the determination of a set of Plant States that encompass all conceivable conditions in which a significant release of hazardous material to the environment can be postulated. This has been done for the ITER tokamak, leading to a set of 10 representative Plant States. Event sequences leading to such states generally require the independent failure of two or more confinement barriers, and are thus of very low frequency. A further set of 16 Plant States have been identified in which there is no significant release, but in which an ITER confinement function is challenged. The PIE–PIT can be used to find the most significant challenges, and eventually to lead to a new definition of a set of bounding events for future safety analyses.