Numerical Simulation and Analysis to the Behavior of Inner Hole Defect of Integral Top Cover for Pressure Vessel

The integral top cover for nuclear reactor pressure vessel is an important force component in the pressure vessel. It works under the HPHT and radiation long time, which increases forging difficultly and needs extremely high quality. Due to the effect of bi-directional tensile stress in spherical part during the shape forming stage of the integral top cover, it is easy to make holes and other defects of the blank extend. Then, it is necessary to study the behavior of the inner hole defect of integral top cover. This paper, by numerical simulation technology, concrete analyses the volume of the hole defect, the size of the hole defect and variation of the hole edges in the stress-strain fields during the shape forming stage of the integral top cover. It researches the control scope of the original size of blank holes when the integral top cover forging meet the requirements of the flaw detection. Research results show that, according to the requirements of volume and maximum size permissible value, the diameter of holes in the integral top cover blank should be respectively less than 1.8 mm, 1.5 mm.