Study On The Impact Of Meteorological Conditions On The Reliability Of Passive Systems In Nuclear Power Plants

The use of passive systems simplifies the design of safety systems in nuclear power plants and reduces system equipment redundancy.At the same time,it makes full use of natural driving force and does not rely on active equipment to reduce system operation failures caused by power,mechanical and valve failures,reduces the possibility of human error,which greatly improves system operation reliability and economy.The establishment of natural circulation is affected by many factors.The atmosphere as the ultimate cold source and heat sink,if the changes in meteorological conditions cause the natural driving force that the system depends on deviates from the design value,the natural circulation cannot be established,which will cause the performance of the passive containment cooling system(PCCS)to decline or fail,endangering the integrity of the containment.Therefore,it is very important to study the influence of meteorological conditions on the reliability of passive systems in nuclear power plants.This paper mainly studies the influence of meteorological conditions on the reliability of the PCCS.Based on previous research and the suggestions of meteorological experts,this paper selects meteorological factors such as air temperature,air pressure and humidity for research.Firstly,the Apriori association rule algorithm was used to mine the meteorological data,and some rough association rule results were obtained.According to these rules,the relationship between various meteorological elements was analyzed and the factors to be considered in the accident analysis were guided.The correlation between these meteorological factors is analyzed and the relationship between air pressure and air temperature is obtained by fitting.The fitted relationship between the air pressure and air temperature was introduced into the self-developed passive containment cooling system thermal-hydraulic(PCCSTH program for calculation and analysis after the accident.Under the two design basis accident conditions of hypothetical loss-of-coolant accident(LOCA)and main steam line break(MSLB),some specific parameter values such of discharge flow,air temperature,air pressure and relative humidity are selected and using the PCCSTH program calculate to analyze the impact of the uncertainty of these meteorological factors on the reliable operation of passive systems.The calculation results show that with and without considering the correlation between air temperature and air pressure,changes in air temperature have a certain effect on the peak pressure in the containment after the accident.When the MSLB accident occurs under extreme high temperature weather without considering humidity,the peak pressure in the containment exceeds 0.5 MPa if the air temperature and air pressure correlation is not considered.However,when considering the correlation between air temperature and air pressure,the peak pressure in the containment is slightly lower than 0.5 MPa,which does not exceed the design value,which can ensure the integrity of the containment.The analysis also found that changes in air temperature and air pressure have two orders of magnitude higher impact on the peak pressure in the containment than relative humidity.