A coolant suitable for small long life natural circulation lead-based fast reactor

Background: Small long life natural circulation lead-based fast reactor has broad development prospects in the fields such as marine nuclear power, portable power, thermal-electric co-generation in remote areas, seawater desalination, et al., and is one of the important development directions of lead-based fast reactor. Purpose: This study aims at the coolant selection for the design goals of long life, miniaturization and natural circulation of lead-based fast reactors. Methods: First of all, refer to the ALFRED design scheme of EU small lead based demonstration fast reactor, a 100 MWt lead-based fast reactor core model was taken as design paramenters. Then, Pb element/mixture and Pb-Bi mixtures were selected for study by using three dimensional transport Monte Carlo code (RMC) developed by the reactor engineering calculation and analysis laboratory of Tsinghua University. High temperature nuclear database ADS-2.0 released by the International Atomic Energy Agency was employed to calculate and analyze the burnup characteristics, reactivity coefficient and effective delayed neutron fraction of lead based fast reactor cores with different coolants. Finally, the neutronics characteristics of different coolant cores and the natural circulation characteristics of different coolants were analyzed and compared. Results: The results show that the neutron capture cross-section combined with Bi is smaller due to the small inelastic scattering cross-section of 208Pb in the high-energy region and the extremely small neutron capture cross-section in the middle and low energy regions. The 208Pb-Bi cooled lead-based fast reactor core has the lowest burnup reactivity loss and the best breeding performance with large negative void coefficient, coolant temperature coefficient and large effective delayed neutron fraction in at 30 EFPY operating cycle. Conclusions: The 208Pb-Bi cooled lead-based fast reactor core can be loaded with a lower enrichment or a smaller amount of fuel, which is beneficial to miniaturization, long life and inherent safety of the core; compared with Pb, 208Pb-Bi cooled lead-based fast reactor has stronger natural circulation capability, weaker material corrosion, and wider operating temperature range, which is conduvtive to the safe operation and maintenance of reactor. © 2022, Science Press. All right reserved.