Examination of radiation damping of nuclear power plants

A simple and handy method by which the underground dissipation damping of the fundamental mode of nuclear reactor buildings can be calculated. Using this method, the authors examined the damping of an existing nuclear reactor building, and checked another nuclear reactor building which was in the design stage. A system which consists of a rigid base and one mass point above it was considered as a model. The fundamental equations to obtain the natural frequency, the proper damping factor and the proper mode of the system are described. These equations were derived by the Tajimi's solutions for vibration admittance. A model for nuclear reactor buildings is a system of three mass points on a rigid base. The three mass points correspond to an external shield, a containment vessel and an internal concrete. The damping factors and the natural frequencies were obtained for the existing building and the building in the design stage. The calculated results were compared with the experimentally obtained results of the existing building. As the results of the investigation, it was confirmed that, depending on the configuration of reactor buildings, larger damping than in usual practice might be expected on the basis of underground dissipation damping. (Kato, T.)