Research on Transient Safety Characteristics of Lithium-cooled Fast Reactor with Stirling Thermoelectric Conversion System

Abstract: [Background] The lithium-cooled fast reactor coupled with the Stirling thermoelectric conversion system is suitable for space nuclear power systems due to its high energy density and reliability. However, the complex multiphysics coupling analysis under transient accident conditions poses challenges. Existing studies primarily focus on steady-state performance, lacking systematic transient analysis of accidents related to the power conversion model, which limits the evaluation of system safety and self-regulating capabilities. Therefore, developing a high-fidelity transient analysis program to validate the safety characteristics of the lithium-cooled fast reactor Stirling system is crucial. [Purpose] This study aims to develop the NUSOL-LMR-Li transient analysis program for the lithium-cooled fast reactor Stirling system and analyze accident scenarios to validate its safety and self-regulating capabilities. [Methods] Firstly the NUSOL-LMR-Li program was developed, which integrates models for core power calculation, thermal-hydraulic analysis, heat conduction in structural components, and thermophysical properties of liquid lithium. The core Stirling thermoelectric conversion model was established using the Schmidt isothermal analysis method, enabling precise coupling with the lithium-cooled fast reactor. The fully implicit discretization of convection-diffusion algorithm was validated through a single-tube flow case, demonstrating stability independent of time step size. The core power model achieved computational errors of 0.53% and 0.32% under positive and negative reactivity insertion conditions, respectively, showing high agreement with analytical solutions. The Stirling power conversion model was verified using the NASA RE-1000 Stirling prototype and SP-100 system loop tests, with a maximum error of 3.8%. Simplified modeling was conducted based on the SP-100 reactor, and transient analysis was conducted for typical accident scenarios, including reactivity insertion and regenerator blockage, to evaluate the system’s response characteristics. [Results] The results demonstrate: (1) A 0.1$ reactivity insertion increased core power to 534 kW, stabilizing at 466 kW via negative feedback, with an outlet temperature rise limited to 14.7 K； (2) Regenerator blockage reduced Stirling efficiency to 22.24%, but the system reestablished thermal balance by lowering the hot-end temperature to 1023 K and raising the cold-end to 692 K, recovering efficiency to 26.8%. [Conclusions] The NUSOL-LMR-Li program validated the self-regulation and fault tolerance of the lithium-cooled fast reactor Stirling system, providing an efficient tool and theoretical support for space nuclear power safety design.