Research On Uncertainty Analysis Of CEFR OTSG Thermal-Hydraulic Input Parameter

The safety analysis of nuclear power plants is an indispensable part of the safety system efficiency evaluation.As an effective tool for safety analysis,the system thermal-hydraulic program is used to simulate the transient action of power plant and its safety system under accidence.As thermal-hydraulic uncertainties exist naturally,the physical abstraction,modeling and calculation in thermal-hydraulic simulation will take in uncertainties and finally affect the calculation results.Thermal-hydraulic parameters uncertainty analysis can contribute to improve the credibility of thermal-hydraulic calculation results,reduce the safety margin reasonably and improve the safety and economy of the power station,thermal-hydraulic parameters uncertainty analysis is of great significance.In this paper,the thermal-hydraulic uncertainty analysis of China Experimental Fast Reactor OTSG is researched,while according to the thermal-hydraulic uncertainty sources' characteristic classification of sources and classification rules are provided.In order to study the character of maximum OTSG output pressure and varying of OTSG output pressure while considering uncertainty exists,LOFW accidence is simulated by CEFR simulation program powered by Harbin Engineering University in this paper.According to operation experience,design instruction and the study of the fast reactor OTSG system with its thermal-hydraulic model,five input parameters plant uncertainty affect output pressure most are confirmed with their statistical character,which provides the data foundation for thermal-hydraulic uncertainty analysis.Compared with other uncertainty analysis methods,statistical sampling method is chosen in this paper.According to statistical sampling method,uncertainty and sensitivity analysis code is finished.After inputting uncertainty samples into CEFR simulation program,related OTSG output pressure data are calculated.Uncertainty and sensitivity analysis is finished after analyzing the change of uncertainty arrange and the maximum output pressure uncertainty during accident process.In order to study the effect of parameter classes on uncertainty propagation,control pressure of main throttle valve,machining error of inlet and outlet in OTSG are taken into account,uncertainty parameters are divided into safety parameters,structural parameters,thermal-hydraulic parameters and safety control parameter.The sensitivity analysis is provided in each class,after deducting the sensitivity inter-disturbance between input parameters by input parameters classification.Considering to the influence of input parameter uncertainty of plant data,it is proved that output pressure will not exceed its safety limited value during the loss of feedwater accident.Among all of the uncertainty source in this research,uncertainty of outlet pressure of steam generator is the most sensitive to the atmospheric relief valve opening pressure.Meanwhile,the sign of thermal-hydraulic parameters' sensibility isn't changed after input parameters classification.The absolute values of parameters' sensibility increased obviously,except safety control parameter.