Loss of vacuum accidents in ITER

A loss of vacuum event is postulated for ITER as follows: failure of windows/valves in a vacuum vessel penetration line into a room filled with air. Part of the mobilized tritium and dust is transported into the room because the air inside the vacuum vessel heats up. It is assumed that operators will start maintenance detritiation pumps after one hour to restore low pressure inside the vacuum vessel. Continued operation of this system is necessary to control the situation until the leak is plugged. Environmental stack releases are about a factor of five below ITER release limits. To investigate ultimate safety margins, a loss of vacuum with a 0.2 m 2 cross-sectional area is postulated into a room without connection to the stack. An air exchange flow (velocity ∼1 m/s) is established driven by the density difference between hot air within the vacuum vessel and cold air in the connected room. Operation of the maintenance detritiation system after one hour limits the environmental ground level releases below the no-evacuation threshold.