Research On Seismic Properties Of Nuclear Safety Class 3 Suspended Polyethylene Pipe

Nuclear power has the advantages of economy,environmental protection,and stable power generation.It is an effective way to solve the problems of petrochemical energy shortage and environmental degradation.Pressurized water pipes of nuclear power plants generally use traditional materials such as carbon steel,cast iron,and concrete.Due to electrochemical corrosion and microbial corrosion,the pipes have undergone different degrees of corrosion and scaling,and the cost of regular inspection and maintenance are extremely high.High density polyethylene(HDPE)pipe has the advantages of corrosion resistance,long life and good toughness.In recent years,it has been applied to non-nuclear safety related cooling water system in nuclear power plants.In order to ensure the safe operation of nuclear power plants,various possible accidents need to be considered.In particular,it is necessary to ensure the functional integrity of HDPE pipe after a Safe Shutdown Earthquake(SSE).HDPE pipe has strong time dependence,and the response under seismic loads is different from that of metal pipe.Therefore,the seismic analysis method for metal pipe cannot be used directly.The analysis methods and test data of the seismic performance of suspended HDPE pipe are still lacking,which limits the application of HDPE pipe in nuclear safety related systems.This paper is supported by the school-enterprise cooperation project "Research on HDPE Pipes for Seawater Cooling Systems in Nuclear Power Plants" and "Seismic Test of HDPE Pipes for Cooling Water in Nuclear Power Plants".In response to the need for suspended HDPE pipe transformation of Hualong One of Fuqing Nuclear Power Plant,the seismic performance of HDPE pipe is studied.The main works are as follows:(1)According to the nuclear power plant design documents,the HDPE pipeline models of SEC system are established to calculate the stress state under different loads,including gravity,thermal expansion/contraction,building anchor motion and seismic.Based on the calculation of the inherent model and seismic stress of HDPE piping system,the fixed position and constraint form of supports and hangers are selected and optimized.The section forces,bending moments,and overall stress distribution under various loads before and after the modification of supports and hangers are calculated and the stresses are checked.The response spectrum method is used to analyze seismic loads and determine the most risky key sections of HDPE pipeline system.(2)More accurate local modeling of risky key sections.For the risky key sections,more accurate models are conducted by simulating the mechanical response under different loads including gravity,internal pressure,thermal expansion/contraction,and seismic loads.The stress distributions under different types of single loads and combined loads are subsequent calculated.The appropriate width of supports and hangers is selected by the comparison of calculation results,which can reduce stress concentration and facilitate construction and installation.The stress peaks of three key sections under different loads before and after the modification of supports conditions were compared.The influence of structure,temperature and load on the stress state of key sections are discussed.The internal pressure has the greatest effect on stress state of the pipe sections.The effect of temperature is small and structurally related,and the effect of gravity is minimal.(3)Detailed schemes for seismic test are formulated for HDPE pipe in nuclear power plant.The artificial wave acceleration time-history spectra of earthquakes are designed as input load of the vibration test.Finite element analysis method is used to simulate dynamic response process of test section model under test seismic wave.Therefore,the sensor data under test conditions of seismic waves and water pressure are predicted.When HDPE pipe encounters an earthquake,the main influence of stress state is still internal pressure,and seismic wave will cause the maximum to fluctuate within 3%.HDPE pipe can relieve the acceleration caused by vibration and has good seismic resistance.