Effect Of Thermal Stress On Fatigue Crack Propagation Of AP1000 Pressure Vessel

Pressure Vessel(RPV)operates in the environment of elevated temperature,high pressure and high-level radioactivity.Therefore,the defects are inevitable during the operation process.Since RPV is the only non-replaceable equipment in nuclear power plant,it is significant to maintain the integrity of the primary circuit during the operation process.A common cause of failure of RPV is fatigue crack,which usually occurs and extends at stress concentration points such as the inner wall of RPV inlet and outlet pipe.Therefore,it is essential and significant to study the fatigue crack propagation law of RPV inlet pipe.Aiming at the structure and stress condition of AP1000 pressure vessel,the model and loads of the RPV are established.The thermal stress and deformation of pressure vessel,especially the orifice part,are analyzed.The stress condition and service life of pressure vessel under different working conditions are simulated.The dangerous areas of pressure vessel are found out.The fatigue life of pressure vessel under different cyclic stress amplitudes and average stress levels is analyzed.The stress intensity factor is evaluated by inserting cracks into the stress concentration nodes of the RPV.Then the influence factors of crack growth are analyzed,and analyze the effects of crack shape and design accident of the RPV on the stress intensity factor during the crack expansion.The results show that both cyclic stress amplitude and average stress level lead to the decrease of fatigue life of the RPV.The influence of average stress level is low but not negligible.The larger ratio of long axis to short axis of crack is,the greater the value of stress intensity factor of crack is,and the stress at the front of crack is stronger.The change of degree factor is gentle.Under the condition of more severe pressure change,the stress intensity factor level of crack is higher.