An overview of the shielding optimization studies for the TRIUMF-ARIEL facility

The Advanced Rare IsotopE Laboratory (ARIEL) facility, dedicated to Radioactive Ion Beam (RIB) production via the Isotope Separation On-Line (ISOL) technique, is currently under construction at TRIUMF. The facility is to host dual target stations that will operate simultaneously, including a 500 MeV proton beam from the main TRIUMF cyclotron and a 50 MeV electron beam from an Electron Linear Accelerator (e-linac). The proton target station will operate a symbiotic medical target in series with the ISOL target. The ARIEL facility features a compact shielding envelope and as a result its optimization relied extensively on simulations generated using the Monte Carlo particle transport and interaction code FLUKA. Dose rate maps were produced of prompt radiation associated with beam losses and expected normal operations. Maps of transient fields were also generated considering radiation sources requiring transport within the facility which include radioactive waste generated in the course of normal operations. Activation studies were also conducted to estimate the amount of residual radioactivity contained in shielding materials at the time of decommissioning. Simulation results are primarily used to inform the ongoing design and construction of ARIEL; at present, the entirety of the proposed facility shielding has been validated by FLUKA simulation data. The specification of shielding geometry and the selection of materials relied extensively on engineering support through verification of CAD models and material sampling to optimize solutions for design simplicity and economy. Normal operation and failure scenarios were both evaluated, with optimized shielding materials and thicknesses selected considering the nature of the radiation fields present and their impact on room occupancy. Finally, a decommissioning plan has been defined based on the anticipated ARIEL lifetime, the characterization of structural activation, and a general disposal strategy. While ARIEL is still under construction and significant progress has been made, the ongoing radiation modelling has enabled validation of the current shielding design for nominal operation. Moreover, the systematic studies performed were paramount in defining the optimal strategies to adopt from target storage to that for decommissioning of the facility.