Impact of risk analysis on ITER nuclear buildings internal layout

The internal layout of ITER nuclear buildings (Tokamak, Tritium, Hot cell and Radwaste buildings) is the result of an iterative process. Notwithstanding civil engineering requirements, technical and functional requirements for the processes housed in the buildings, the internal layout must also take into account safety requirements and workers protection requirements in normal, incidental and accidental conditions. Potential hazards and constraints result in the definition of various zonings. Each room is classified depending on the level of risk induced by normal and incidental or accidental conditions : - radiological exposure to tritium, and activated products → radiological zoning - exposure to beryllium (vacuum vessel blankets) → beryllium zoning - exposure to electromagnetic fields during plasma shots → electromagnetic zoning - fire hazard : fire compartmentalisation - explosion hazard → anti-blast zoning - waste treatment → waste zoning Prevention of common mode failure due to internal hazards (fire, flooding, load drop ...) for redundant safety important components is also taken into account by geographical separation or by installation of protections between components (either in the same room or preferably when possible by segregation in different rooms). The designer also has to take into account access requirements to equipment and circulation rules for personal, material and substances in ITER nuclear buildings. Risk analyses are performed in the Preliminary Safety Report in order to demonstrate that the layout of ITER nuclear buildings allows to meet the safety objectives and takes into account the requirements associated with the zonings classifications and complies with the regulation. When necessary, modifications are implemented in the design. For example, recent layout modifications were included in the tritium building : utility rooms (electrical supply) were transferred outside the radiological hazard zones. A direct access from the outside was provided, so that personal can access these electrical rooms without having to go through radiological zones. (author)