Assessment of stresses in reactor pressure vessels and main circulation pipes in recurring inspection

For materials evaluation and decision on the extent of nondestructive materials testing the stresses ocurring during steady and non-steady state operation have to be determined with respect to both quantity and type of component affected. In the case of the primary circuit the reference stress as well as the strains at all points of discontinuity in the conduit can be determined by using the computer programmes of tube statics. The quantities thus determined allow to find the point of maximum reference stress on the tube circumference as well as to perform further calculations of the stresses in sections close to branchings. In the case of reactor pressure vessels the stresses are determined during steady and non-steady operation. Assessment of thermal stresses in the non-steady state is based on the determination of temperature distribution along the reactor wall and of their maximum temperature differences. This determination is based on the calculation of the temperature field using the TEMFEL code. Stresses and strains due to internal pressure, forces and moments of the head closure boltings, axial changes in temperature and linear changes in the wall temperature are determined on the basis of the ROTSYV shell code. The calculation of thermal stresses with non-linear temperature distribution over the reactor wall for homogeneous and plated cylindrical and spherical walls is made by using the TEMBA codes. The stresses determined can be superposed on the reference stress by use of the TEMBA code. Results are presented and interpreted. (author)