Transient safety characteristics of lithium-cooled fast reactor with Stirling thermoelectric conversion system

BackgroundThe lithium-cooled fast reactor coupled with the Stirling thermoelectric conversion system (STCS) 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.PurposeThis study aims to develop the NUSOL-LMR-Li transient analysis program for the lithium-cooled fast reactor STCS and analyze accident scenarios to validate its safety and self-regulating capabilities.MethodsFirstly 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. Then, the Schmidt isothermal analysis method was employed to establish core Stirling thermoelectric conversion model to achieve precise coupling with the lithium-cooled fast reactor, and 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. Even under large step positive reactivity insertion, the error remains within an acceptable range and increases slowly over time. Finally, the Stirling power conversion model was verified using the NASA RE-1000 Stirling prototype and SP-100 system loop tests, and 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.ResultsVerification results for RE-1000 Stirling prototype and SP-100 system loop show a maximum error of 3.8%. Analysis results on the basis of SP-100 reactor demonstrate: 1) A 0.1 $ reactivity insertion increases 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 reduces Stirling efficiency to 22.24%, but the system reestablishes thermal balance by lowering the hot-end temperature to 1 023 K and raising the cold-end to 692 K, recovering efficiency to 26.8%.ConclusionsThe NUSOL-LMR-Li program proposed in this study demonstrates that the lithium-cooled fast reactor with STCS exhibits robust self-regulation and fault tolerance under transient accidents, providing both a high-precision analytical tool and theoretical support for the safety design of space nuclear power systems.