Dose rate produced by secondary radiation at the SwissFEL free electron laser facility

A new large-scale facility is currently in the design phase at the Paul Scherrer Institute. SwissFEL is foreseen to accelerate electrons up to an energy of 7 GeV with a pulsed time structure. Unavoidable interactions of the primary beam with beam line components create secondary radiation. The shielding of the accelerator vault has to reduce the radiation level for accessible areas in compliance with legal constraints. In addition, the position and layout of cable ducts and infrastructure shafts through the shielding of the accelerator tunnel have to be investigated from a radiation protection point of view. In this work, the dose rate distribution inside the accelerator vault has been evaluated for expected beam loss scenarios (normal and diagnostic mode of operation) based on Monte Carlo calculations. By means of the multi-particle transport code FLUKA, a simplified model has been defined and the results have been parameterized. From these, a dose rate evaluation has been extracted for different positions inside the accelerator tunnel. The results can be used to investigate the leakage of radiation through cable ducts and infrastructure shafts for different design layouts or modes of operation.