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Radiation transport calculations for the European Spallation Source accelerator environment

A central component of the European Spallation Source is the high-power proton accelerator. The accelerator aims in the future to provide 2 GeV protons to a rotating tungsten target for the production of neutrons at 5 MW of average beam power for neutron scattering studies. Extensive shielding surrounds the accelerator, in order to provide sufficient safety for the public and workers against radiation produced along it's length. This largely comprises several meters of soil, called the berm, and concrete structures located around the accelerator tunnel. However, due to the need for access to the accelerator, during maintenance and connections for other utilities, the shielding contains a number of penetrations which leads to weaknesses in localized areas. For these reasons, shielding design of such a facility must take care to address issues related to both the deep-penetration of the radiation through thick shields, while at the same time accounting for the streaming nature of the radiation through ducts and chicanes. In addition, radiation produced from activated components of the accelerator also poses risks for workers and public. For example, activated magnets will need maintenance and workers may need to access areas where activated water circulates. Thus, activation analyses are also needed in combination with the prompt-dose rate estimates for a complete analysis. In this summary, we present the results of a series of such studies carried out on various components around the ESS accelerator.