Crack Propagation Analysis For Pressure Vessel Nozzle

As the only non-replaceable equipment in the whole life of nuclear power plant,the reactor pressure vessel is always in the harsh environment of high temperature,high pressure and strong neutron irradiation during operation.In engineering practice,the reactor pressure vessel inevitably have defects in the manufacturing process,and these defects may cause fatigue crack propagation in the complex environment when the nuclear power plant is operating.Therefore,it is very necessary to study the crack propagation of reactor pressure vessel with defect.In this paper,the thermal stress of the AP1000 reactor pressure vessel under the temperature load are calculated,and the thermal stress distribution of the pressure vessel is obtained.The result is compared with the situation that is only subjected to internal pressure load,and find out the stress concentration area of the reactor pressure vessel.The finite element model of reactor pressure vessel with inlet-nozzle angle crack is established,as well as the stress intensity factor(SIF)along the crack front is calculated.The results obtained are compared with those calculated by weight function method.Then the influential factors of the angle of crack propagation are analyzed:firstly,analyze the thermal stress and crack angle influence on the initial stress intensity factor of crack,then the crack propagation for 0°,10° and 15° are studied,and get the influence of thermal stress on crack propagation,finally,the research on crack spacing of parallel double crack propagation of 10 mm,20 mm and 30 mm are studied.The results show that the stress concentration area of the reactor pressure vessel is located in the intersection area between the cylinder and the inlet nozzle.Because the peak stress in this area exceeds the yield limit of the material,it is easy to crack under the action of periodic load.The SIF results obtained are closed with those calculated by weight function method With the increase of the angle between the crack and the pipe inlet,the stress intensity factor of the crack at the pipe inlet decreases gradually,and the stress intensity factor of the crack with thermal stress is smaller than that without thermal stress.In the whole process of crack propagation,compared with no thermal stress,under thermal stress the stress intensity factor of crack slightly smaller,the nozzle angle of crack in the extension process gradually tends to be the entrance,type Ⅱ and type Ⅲ stress intensity factor decreases and neglect when compared to type Ⅰ,and crack extension into type Ⅰdominant;Through the study of the extension of parallel double crack simulation,when initial double cracks are close,the reciprocal inhibition between the cracks is strong.When short crack extension stopped,long crack stress intensity factor and crack propagation distance growth step is larger,with the increase of distance,the reciprocal inhibition between the cracks is weak.