ITER reference accidents

Abstract Reference accidents are selected to envelope possible accident sequences to confirm the adequacy of ITER's safety design. Analyses of ITER reference accidents were carried out starting from postulated initiating events (PIE) to all consequential failures including environmental releases, if any. In case of plasma control malfunctioning, up to 3.3 GW of fusion power can be reached transiently, however, no radiological consequence is expected from those transients. Assuming multiple first wall pipe failures, the pressure suppression system limits the maximum pressure within the vacuum vessel to below 0.5 MPa. Long-term decay heat removal is assured by the vacuum vessel cooling system operating in natural circulation. In case of ex-vessel coolant loss with continued plasma burn, the plasma facing components can potentially reach large temperatures. This is avoided by the fusion power shutdown system that terminates plasma burn. A small in-vessel coolant leak with failure of one vacuum vessel penetration line and several confinement options are investigated to show compliance with release limits. Failures in the magnet system are analyzed and their impact on other systems such as damage to neighboring confinement barriers are investigated by postulating air, water and helium ingress into the cryostat. Failures in the tritium plant are analyzed to demonstrate the adequacy of confinement. Radioactive releases for all reference accidents are shown to be well below conservatively defined design guidelines.