Nuclear Power Plant Safety Limit Analysis Method Of Comparative Study And Application

The DNBR margin is one important parameter of nuclear powerplant design，which presents the safety level of NPP. The increase ofDNBR margin is benefited for the upgrading of core refuel scheme，andcan provide more flexible for the design and operation of NPP.This thesis analyzes the completely loss of flow accident, as it is oneof the condition II accidents, which affect DNBR most severe. Toinvestigate the design features of300MW NPP, RELAP5/MOD3wasutilized to systematically perform the analysis of completely LOFA. Atthe same time, a subchannel code VIPRE was used to build thesubchannel model of the reactor core.During the analysis of NPP accidents, the models and plantparameters all have some uncertainties. The ITDP method canquantitative the uncertainties of input parameters through mathematicalanalysis and sensitivity analysis. Sampling calculate the input parametersbased on the non-parameter and parameter method, then get the tolerancelimits and one side confidence limit under certain probability level and confidence degree through statistical theory.This thesis applies the STDP method、ITDP method、non-parameterand parameter statistical method based on Wilks formula tolerancelimitation to calculate the DNBR limit of300MW NPP in the condition ofcompletely LOFA. seven parameters were choose which are related toDNBR as initial input parameters with consideration of their uncertainty,such as the coolant flow、the bypass flow of nuclear core、the reactorpower、the average temperature of coolant、the pressure of the nuclearcore、the nuclear enthalpy rise factor and the engineering enthalpy risefactor.The accident is simulated and calculated based on RELAP5/MOD3and the subchannel program VIPRE. By the theory of nonparametricstatistics, make59groups sampling calculation of the input parameters,theDNBRnonparametric，95/95within the accident condition is2.163. At the sametime, make mathematical statistics analysis of the59groups DNBR, theresults of theχ~2distribution fit test show DNBR distributed normally,theDNBR95/95(the single side lower limit of the95%DNBR at95%confidence level) is2.165. The sensitive factor of each parameter of theITDP method can be calculated, the DNBR limitation of the ITDPmethod can also be calculated according to sensitive factors. The resultedshow:DNBRI TDP(the DNBR limitation of the ITDP within accident) is2.229,7.29%DNBR margin can be gained compared to STDP method which is used in nuclear power plant to analyze thermal-hydraulic.Compared the DNBR limitation of three methods, we can seeDNBRnonparametric，95/95<DNBR95/95<DNBR ITDP， this indicates that non-parametercan provide relatively lager DNBR margin. Compared with the ITDPmethod, the non-parameter and parameter method can reduce theconservation during the process of analysis, and gain more safety margins,which have reference significance in choosing quantitative methods ofparameter uncertainty during the process of improving the economy ofnuclear power plants.