Uncertainty analysis of loss of coolant flow accident in lead–bismuth reactor using subchannel code

[Background] Subchannel codes constitute an important computational tool in the field of reactor thermo-hydraulics. Uncertainty analysis methods can be used to effectively identify and quantify the uncertainties of code input parameters and model assumptions, thus improving the reliability of the code so as to provide a more reliable reference for thermo-hydraulic parameter design. [Purpose] This paper aims to present an uncertainty analysis of a 10 MW small lead-bismuth reactor in steady-state and transient loss-of-flow accident scenarios by using the subchannel code SUBCHANFLOW. [Methods] First, a full reactor core subchannel was modeled, and the input parameters that affect the target parameters were identified. Second, the optimal Latin hypercubic sampling method was used for sampling within the distribution range of the input parameters, and the samples were imported into SUBCHANFLOW to obtain the uncertainty bands for the steady-state and transient loss-of-flow accident scenarios. Finally, gray correlation analysis was employed to evaluate the steady-state and transient sensitivities. [Results] The computational results indicate that the uncertainty bands of the target parameters envelop the nominal values in both the transient and steady-state cases. In the transient case, the maximum temperature tolerance upper limit of the pellet is 674.55 ℃ and that of the cladding is 618.31 ℃. Further, the calculation accuracy of each parameter is essentially below 7%. The uncertainty in the target parameters mainly originates from parameters such as the inlet temperature, fuel rod height, outlet pressure, total power, and thermal conductivity of the cladding, with the inlet temperature having the most significant effect. [Conclusions] This study demonstrated the computational uncertainty of the SUBCHANFLOW code and the difference in the sensitivity of each parameter to the system response under the steady-state and transient loss-of-flow accident scenarios. The findings help further optimize and improve the design and operation strategy of lead-bismuth reactors, thus enhancing their safety and reliability. © 2024 Science Press. All rights reserved.