Coupled Neutronics And Thermal-hydraulics For PWR Rod Bundle Calculation And Uncertainty Analysis

Pressurized water reactor(PWR)is the most popular commercial nuclear reactor around the world,which contains several coupled physical fields,such as thermal-hydraulics,neutronics etc.As a result,it is necessary to perform thermal-hydraulics and neutronics coupling research and evaluate its thermal-hydraulics and neutronics performance.Also,uncertainty quantification is important for code verification and validation,as well as nuclear safety analysis.In this context,a coupling tool was established based on the commercial computational fluid dynamics(CFD)code Fluent and Monte Carlo neutronics solver MCNP,in order to analyze thermal-hydraulics and neutronics performance of PWR.Python was applied to control the data flux between two solvers,and to realize automated execution of the coupling steps until the convergence critic was satisfied.NJOY2016 was used to process parameters of crosssection database including temperature,format etc.,and to convert the standard ENDF database to the cross-section database required by calculation.By invoking IAPWS-IF97,the coupling system could update the density of coolant online and introduce the negative temperature effect.Besides,both Picard iteration scheme and Newton iteration scheme were applied to the thermalhydraulics and neutronics coupling calculation.Loss of coolant flow accident(LOFA)in PWR was conducted to analyze the coupled thermal-hydraulics and neutronics simulation on transient state.To quantify the uncertainty of output parameter and represent the distribution of output parameter with the presence of input uncertainties,it is necessary to apply an uncertainty analysis process on simulation code.Considering that conventional uncertainty analysis techniques are unable to evaluate multi-physics fields codes due to its high computational resource consumption.Therefore,an enhanced method was proposed to estimate tolerance limits of output parameter.By combining sensitivity analysis and uncertainty analysis together,this method provides a preprocessing to narrow down relevant analysis region and a set of new statistically meaningful minimum sampling size determination formula.Compared with GRS method,this method reduces sampling size significantly.After the validation of this method,it was applied to quantify the uncertainty of peak cladding temperature(PCT)of the coupling system.