Reliability Evaluation Of Control Rod Drive Mechanism Penetration Nozzle And Hold Down Spring Of Pressurized Water Reactor Considering Service Environment

Reactor inner component and control rod drive mechanism as the key equipment in reactor are the important components of nuclear power plant.It is of great significance to study the reliability of the key equipment in reactor for the safe operation of nuclear power plant.The inner components of the reactor can fix and press the radiation monitoring device of the reactor pressure vessel,limit the flow of coolant channel,control the distribution of coolant flow,and play an important role in support,guidance,temperature and neutron measurement.The control rod drive mechanism is the key active equipment in the reactor,which can play the reactor shutdown operation in the case of emergency,regulate the reactor power fluctuation and control the reactivity.Due to the long working time of the key equipment in reactor,it is not only subjected to high temperature,high pressure,high radiation and other harsh conditions during the service environment,but also subjected to high-speed erosion of coolant.Especially with the extension of service time,the combined action of one or more failure mechanisms will affect the structural performance of the equipment.For example,once the control rod driving member fails,it will cause rod sticking and rod dropping accidents.Such performance changes will affect the reliability of equipment and lead to serious consequences,which will directly threaten the safety of the reactor.In addition,the failure of the key equipment in reactor is a slow cumulative change process.Improper design,manufacturing,installation,operation and maintenance will lead to more than expected limits,and will accelerate the failure process under severe conditions.The structure of the key equipment in reactor is complex,with tens of thousands of parts and components,and the equipment may have multiple failure modes.The failure of equipment is difficult to detect and intervene,and once the failure will seriously affect the safety and economy of nuclear power plant.With reliability analysis as the core,this paper conducts in-depth research on reliability evaluation methods and application analysis around several problems of the key equipment in reactor.The main research contents are as follows:(1)Research on the reliability evaluation method of the key equipment in reactor:Firstly,in view of the safety function and service environment of the reactor equipment,through the reactor equipment severity evaluation method,the reliability severity classification of the equipment and the selection of the key equipment in reactor are given;Then,according to the possible failure mechanism and failure mode of the equipment,the limit state function equation was constructed,and the reliability was solved by analytical method or numerical simulation method.Finally,the reliability evaluation method of the key equipment in reactor based on probability evaluation technology is proposed.(2)Reliability application research of typical key equipment in reactor:Considering the control rod drive mechanism penetration nozzle under stress corrosion,primary water stress corrosion,radiation load and other harsh environment,the limit state equation of leakage failure and fracture failure of the nozzle was established,and reliability sensitivity analysis was conducted.For the failure of the hold down spring of the key equipment in reactor,the fatigue model was established by combining the SWT model and Landgraf model,considering the stress relaxation during service and the effect of radiation on the material properties.Based on simulation,the Kriging model was used to predict the stress and strain function values,and the reliability evaluation was carried out according to the generalized stress-intensity interference model.It can assist to determine the safety detection cycle and detection focus of the key equipment in reactor.