Sensitivity Analysis Of RELAP5-3D Based PWR Modeling

The RELAP5-3D code was developed by the Idaho National Engineering Laboratory in US for the transient analysis of reactor systems accident.The program inherits the advantages of the original RELAP5 code series,and the three-dimensional thermal-hydraulic model and three-dimensional neutron kinetics model were added in.In order to find the differences between the latest additions and the original one-dimensional thermal-hydraulic models and point reactor neutron kinetics model,in this thesis,the typical 600 MW PWR nuclear power plant models were built in the newly added three-dimensional component and the original one-dimensional component respectively.Comparison between the steady parameters and transient parameters of the two models has been made.In this thesis,three models have been set up: the traditional conservative one-dimensional model,the quasi-three-dimensional model and the three-dimensional model.Sensitivity analysis has been conducted on aspects of the model parameter settings,model selection and node division methods.The results showed that: in the quasi-three-dimensional model,YZ coordinate data make the transient,steady-state parameters and trends closer to the three-dimensional model;the circumferential and radial loss coefficient do not have a significant effect on the steady-state parameters,but the parameters of the accident transients can be influenced greatly.The settings of junction and boundary volumes as well as the threedimensional flag are all sensitive parameters.The results of five-channel model are more realistic.The increase of nodes number in lower plenum and downcomer make the results more conservative.Assuming that geometry,control logic and thermal parameters are exactly the same,the comparison of the steady and transient parameters in LOCA accidents has been made between the three models.The results showed that: three-dimensional model can reflect the multi-dimensional flow of coolant,and the transient calculation results are relatively conservative.In addition,the comparison between the point neutron kinetics model and the three-dimensional neutron kinetics model has been made in this paper.The results showed that the three-dimensional neutron kinetics model is better in showing space power distribution changes,and the point neutron kinetics model is relatively conservative.