Development of a thoron calibration chamber based on computational fluid dynamics simulation and validation with measurements

Recently, interest in measuring the concentration of (220)Rn in air has increased greatly following the development of standards and the calibration of monitoring instruments. In this study, a (220)Rn calibration chamber was designed and developed at the Institute of Radiochemistry and Radioecology (RRI) based on the computational fluid dynamics (CFD) method implemented in ANSYS Fluent 2020 R1 code at the University of Pannonia in Hungary. The behavior of (220)Rn and its spatial distribution inside the (220)Rn calibration chamber at RRI were investigated at different flow rates. The (220)Rn concentration was close to homogeneous under higher flow regimes due to thorough mixing of the gas inside the chamber. Predictions based on CFD simulations were compared with experimentally measured transmission factors (C(out)/C(in)). The spatial distribution of (220)Rn was dependent on the flow rate and the positions of the inlet and outlet. Our results clearly demonstrate the suitability of the (220)Rn calibration chamber at RRI for calibrating monitoring instruments. Furthermore, the CFD-based predictions were in good agreement with the results obtained at higher flow rates using experimental and analytical models according to the relative deviation, with a maximum of approximately 9%.