The ITER fusion reactor is being built to demonstrate the feasibility of fusion power and will be the largest tokamak in the world. The tokamak cooling water system (TCWS) will extract the heat generated during operations and includes large amounts of piping and equipment such as pumps and heat exchangers (HXs) that are located in a large shielded region on level L3 of the tokamak building. During operation, water in the TCWS will be activated by plasma neutrons and then flow into this shielded region. The activated coolant will in turn activate the steel in the TCWS during operation and result in an activation gamma source and radiation responses that must be assessed to inform equipment selection and maintenance schedules.

The activation of materials in the shielded region of level L3 was assessed at several decay times and for different equipment options using the Oak Ridge National Laboratory (ORNL) shutdown dose rate (SDDR) code suite. The ORNL SDDR code suite implements the rigorous two-step method using the Multi-Step Consistent Adjoint-Driven Importance Sampling (MS-CADIS) method to create effective neutron variance reduction parameters for the photon response of interest. Two different HX designs, shell and tube and shell and plate, were considered, as well as the impact of cobalt impurities in steel equipment.