Abstract: Lead-cooled reactor, one of the fourth generation nuclear power reactor technology, attracts great attention from the world. Due to the significant differences in neutron and γ shielding capabilities between lead coolant and water, radiation field outside the vessel of a lead-cooled reactor differs greatly from that of a pressurized water reactor (PWR). Therefore, the shield design experience from PWRs can't be directly applied to the shield design of lead-cooled reactors. In order to meet the economic shield design requirements of the fourth generation reactors, shield design also needs to be more precise and efficient. Therefore, conducting an analysis of the radiation field characteristics outside the reactor vessel is of great significance. In this study, a typical radial structure of a lead-cooled reactor is chosen, and a 1D computational model is established to analyze the radiation field outside the reactor vessel under normal operation and shutdown conditions by using the RMC program. Firstly, by comparing and analyzing the neutron and γ flux outside the vessel during normal operation of the lead-cooled reactor and PWR, the main contradictions that the shield design needs to be solved during normal operation are identified. At the same time, by analyzing the main sources of γ outside the vessel, the locations and causes of γ generation are determined. Then, the main contributors to the radiation field outside the vessel during shutdown of the lead-cooled reactor are determined by comparing and analyzing the core source terms and reactor vessel activation source terms as well as radiation fields results outside the vessel. Finally, based on the radiation field characteristics of the lead-cooled reactor during normal operation and shutdown, methods for shield design of lead-cooled reactors are proposed. The conclusions in this study are applicable to the shield design of lead-cooled reactors, laying a theoretical foundation for efficient and economical shield design in lead-cooled reactors.

Key words: lead-cooled reactor, radiation field characteristics, activation source calculation