Conceptual core design of a transportable lead-bismuth cooled fast reactor

A conceptual core design of a small transportable long-life lead-bismuth cooled fast reactor core with rated power of 20 MWth was proposed in this study to operate for 18 years without refueling as a remote power supply. In this study, the SARAX code was used to calculate the neutron flux distribution, fuel burnup, reactivity feedback coefficients and kinetic parameters, which was developed by the nuclear engineering computational physics laboratory at Xi'an Jiaotong University. The Monte Carlo neutron transport program OpenMC was used to calculate the control rod worth, and a multi-channel analysis method was used for the core thermal-hydraulic design. In order to reduce the dimension of the reactor core, an innovative fuel assembly design based on tube-in-duct (TID) fuel assembly was proposed with coolant inside the tubes and fuel outside, which achieved a high fuel volume ratio in the core. For radial power flattening, the active region of the reactor core was divided into three regions radially with different sizes of coolant tubes. An optimized core loading scheme was realized within the requirement of core lifetime and the thermal-hydraulics design limit. A liquid absorber control system was implemented using enriched liquid lithium as the neutron absorber, which significantly reduces the core height. In order to lower the initial excess reactivity, fixed replacble absorbers were installed in the control and scram assemblies, and then replaced by fixed reflectors at the 1/3 and 2/3 core lifetime. The thermal design constraints were satisfied during the whole life. The control system and safety system independently provide sufficient shutdown margin. Five typical anticipated transients without scram were analyzed with the quasi-static reactive balance method, and the passive safety characteristics of the core was demonstrated preliminarily.