Study of the Operational Radiation Protection of Two Water-cooled Small Modular Reactors (SMR) under Development Using Monte Carlo Methods

Small Modular Reactors (SMRs) are nuclear reactors currently in the research, development, and testing stages. They are designed in response to the growing demand for a economical, safe and emission-free energy supply. The acronym SMR refers to the small size of these fission reactors, compared to conventional nuclear power plants and their modular nature. The aim of this work has been to assess the shielding of two different types of SMRs currently under development, with the goal of ensuring compliance with legal dose limits for both professional staff and public, under stationary operating conditions. Two different types of modular SMRs refrigerated by pressurized water and used to generate electrical energy were studied, WestinghouseSMR®, and NuScale®, respectively. The shielding analysis was conducted using publicly available data and designs. Monte Carlo codes, specifically MCNP6® and PHITS® were employed for the analysis The dosimetric operational quantity selected to assess the shielding effectiveness was the ambient dose equivalent, H*(10), outside the enclosures of SMR considered, aligned with ICRU/ICRP recommendations, as H*(10) is a conservative quantity for area monitoring. Results indicate that, under normal operating conditions, H*(10) levels are well below international limits in areas where permanent staff occupation is expected. With the goal of optimizing the design, several shielding materials and thicknesses were considered.