Determination of Stiffness Characteristics for WWER-1000 Support Components

Abstract

Available approaches to computer justification of safe operation of reactor support components (RSC) are generally presented in the reports justifying RSC lifetime extension at Ukrainian NPPs. The experience of performing such calculations and analyzing the results indicates that there are issues to be improved. Thus, in particular, RSC stress-strain state is not analyzed for all force factors in the available calculations. It is typical for the reports on RSC lifetime extension justification that the strength assessment of the RSC is performed in an axisymmetric formulation (1/30). Meanwhile, a complex asymmetrical load from the main circulation pipelines is not considered, which affects RSC stress-strain state calculations as some stiffness characteristics (horizontal and torsional stiffness) cannot be determined correctly in a 1/30 axisymmetric formulation.
 The paper proposes a methodology for determining RSC stiffness in a complete formulation (without applying symmetry conditions), taking into account all geometric features and the interaction between individual structures and nodes of RSC. Thus, for each RSC (support ring, thrust ring, separating bellows), based on geometric features and types of connection to other components, stiffness to be determined to calculate the forces is defined (six for support ring and separating bellows and three for thrust ring respectively). Single loads in the form of forces and moments were imposed on the remote points connected to corresponding RSC surfaces to determine stiffness. This load made it possible to obtain the displacements and rotation angles of the corresponding remote points, which were used to calculate the stiffness characteristics.
 The described approach was first used in the calculations performed within justification of KhNPP Unit 1.