INVESTIGATION OF STRESS-STRAIN STATE OF WELDED STRUCTURES FROM AUSTENITIC STEEL AT RADIOACTIVE IRRADIATION

摘要

Nuclear reactor reflection shield is exposed to high doses of radiation, leading to its noticeable deformation and closing of the clearance between the reflection shield and cavity wall. This leads to a change of heat exchange in the reactor core that may have hazardous consequences in terms of violation of temperature mode of reactor operation. To evaluate the radiative swelling of the reflection shield, a 2D finite element model was constructed, using calculation algorithms well-tested at the E.O. Paton Electric Welding Institute, in which isotropic volumetric deformations were assigned as radiative swelling. The model nonlinearly takes into account the dependence of radiative swelling of the reflection shield material on irradiation temperature, stressed state and plastic deformations. The model also describes the change of yield limit of welded cavity wall, as a function of irradiation temperature and accumulated radiation dose. After 25 years of reactor operation the maximum value of swelling deformations in reflection shield material is equal to 1,3%, reaching 1.8 after 40 years, and 3.7 after 60 years. Maximum radial displacements of the reflection shield outer surface during reactor operation are equal to 11.2 mm after 25 years, 12.9 mm after 40 years, and 16.1 mm after 60 years. In a more conservative model, not allowing for the history of volumetric deformation accumulation, reflection shield swells by 26% over 60 years of operation that corresponds to even greater radial displacements of reflection shield outer surface in the outward direction. Results on swelling and radial deformations of the reflection shield derived allowing for the stressed state are indicative of a possible contact of reflection shield with the cavity welded wall during reactor operation. Such a contact can greatly affect the stress-strain state of the cavity welded structure, therefore, it requires a more detailed study.