Stress and strain analysis in the plastic fields of a PWR pressure vessel

The pressure vessel of the pressurized water reactor project Champlain has been calculated twice with two different programs of the CEA-SEMT system: the first axisymmetrical and the second on shell elements. Axisymmetrical calculation with the PASTEL program was carried out on a section of the pressure vessel between two inlet points, which means that the structure considered is assumed as cylindrical. The automatically defined lattice was fairly small meshed and contains 8 to 36 triangles in the thickness according to the position amounting altogether to 1705 elements and 992 nodes. The holes of the control rod passage zone in the cover were taken into account. Finally, the connection between the cover and the pressure vessel is represented by a node common to both parts and by forces distributed at the assembling pin fixations and at the tightening bolt points. The behavior of the system is elastic up to 260 bars, plastic calculations were carried out in a series of 20-bars-steps up to 430 bars. Shell element calculation with the TRICO program was carried out on a quarter vessel containing an inlet point of 700mm diameter. The lattice was established automatically and represents 631 shell elements to which are assigned thicknesses varying with the zones of the vessel. The cover-vessel connection at the joint plane and by the assembling pins is represented and tightened at each pressure increment as in the former case. The results obtained with these two CEA programs agree very well. It was possible to show how the plasticity progresses with each pressure step