Abstract
This study aims to ensure the safety of the nuclear power plants. The accidents of leak from the welded zones at the pipe penetration part of reactor vessel or at the coolant pipe are reported at home or abroad. One of the main causes is the welding residual stress. So, it is important to know the welding residual stress for the keeping of high safety of the plants, the estimation of plants life cycle and the plan of maintenance. The welded joints of the nuclear power plants have complex shapes, and the welding residual stresses also have complex distributions three-dimensionally. In this study, the inherent strain method combined with Finite Element Method (FEM) is used to measure the welding residual stresses accurately.
The mock-up is idealized for the welded joint at the pipe penetration part of actual reactor vessel. The inherent strain method is applied to measure the residual stresses. In this method, the inherent strains are unknowns. When the residual stresses are distributed complexly in 3-dimensional stress-state, the number of unknowns becomes very large. So, the inherent strains are expressed with some functions to decrease the number largely. The theory, the experiment process and the analyzed results are explained. The characteristics of the distributions of residual stresses and their production mechanisms are discussed. The inherent strain method gives the most probable values and the deviations of the residual stresses. The deviations are small enough for the most probable values. It assures the high reliability of the estimated results.
