Uncertainty Quantitative Analysis In Coupled Neutronic/Thermal-Hydraulic Calculations Of Pool-type Fast Reactor Based On Computational Fluid Dynamics

It is of great significance to reveal the changing rules of transient parameters of reactors,quantify the uncertainty zones of transient parameters,and explore the important influencing factors of transient safety parameters.The calculation results of system analysis code are conservative,while computational fluid dynamics code can analyze the three-dimensional thermal-hydraulic phenomena of pool fast reactor and reduce the uncertainty brought by model calculation.Therefore,the coupled neutronic/thermal-hydraulic analysis based on CFD code can improve the accuracy of transient parameters and analyze the transient safety characteristics of pool-type fast reactors more accurately.There is an inevitable uncertainty in the coupled neutronic/thermal-hydraulic calculations,which are used for simulating the performance of nuclear reactors,due to the influence of design parameters and initial conditions.The method of "CFD code +uncertainty analysis" is used to uncertainty quantify of the coupled neutronic/thermal-hydraulic of pool-type fast reactors,which can reduce the "uncertainty zone" of calculation results and predict the parameters of the model more accurately.Based on the CFD/PFS code,the uncertainty analysis of unprotected transient overpower(UTOP)accidents in the small modular natural circulation lead-bismuth alloy cooled fast reactor-10MWth(SNCLFR-10)is conducted.This paper introduces the uncertainty sources and uncertainty analysis methods of the coupled neutronic/thermal-hydraulic calculations.In this study,based on the combination of user-defined function(UDF)of FLUENT,a computational fluid dynamics(CFD)code,with the neutron dynamics model,fuel pin heat transfer model,and SIMLAB software,an uncertainty analysis platform called CFD/PFS is developed.The multi-physics coupled code named SIMMER and the severe accident safety analysis code named NTC-2D are used carried out code-to-code verification for CFD/PFS.According to the literature and judgment of engineering experience,25 uncertain input parameters were selected.This was followed by sensitivity and uncertainty analysis of the UTOP accident based on CFD/PFS.Based on the uncertainty analysis of UTOP accident in SNCLFR-10,uncertainty band of target parameters,including peak reactivity,peak power,peak fuel temperature,and peak cladding temperature,were obtained as 95/95.The titular values of transient security parameters were within the bilateral tolerance limits,indicating that the uncertainty analysis of UTOP accident was reasonable.Using the non-parametric statistical method,the calculated 95/95 tolerance upper limit value of the peak cladding temperature is 1208.66 K,and the 95/95 tolerance upper limit value of the peak fuel temperature is 2757.25 K.The sensitivity analysis revealed that the fuel average temperature and the reactivity feedback coefficient are the main sources of uncertainty.In this paper,an uncertainty quantitative analysis platform based on CFD program is established,which can calculate the physical and thermal transient parameters of pool-type fast reactor more accurately and reduce the deviation caused by model calculation.The uncertainty quantitative analysis of transient calculation is carried out,which can provide practical significance for the design and safety assessment of pool-type fast reactor.