Structural analyses on piping systems of sodium reactors(2); Eigenvalue analyses of hot-leg pipelines of large scale sodium reactors

Furuhashi, Ichiro*; kasahara, Naoto

Two types of finite element models analyzed eigenvalues of hot-leg pipelines of a large-scale sodium reactor. One is a beam element model, which is usual for pipe analyses. The other is a shell element model to evaluate particular modes in thin pipes with large diameters. Summary of analysis results: (1)A beam element model and a shell element model evaluated the same mode for the first order natural frequency. A beam element model is available to get the first order vibration mode. (2)The maximum difference ratio of beam mode natural frequencies was 14% between a beam element model with no shear deformations and a shell element model. However, its difference becomes very small, when shear deformations are considered in beam element. Beam analysis Beam analysis Shell analysis Shear ignored Shear considered Shear considered The first order X-directional horizontal mode 13.47Hz 12.03Hz 11.84Hz The first order Y-directional horizontal mode 13.51Hz 12.06Hz 11.82Hz The first order Z-directional vertical mode 46.33Hz 45.33Hz 43.75Hz (3)In the first order horizontal mode, the Y-piece acts like a pendulum, and the elbow acts like the hinge. The natural frequency is strongly affected by the bending and shear rigidities of the outer supporting pipe. (4)In the first order vertical mode, the vertical sections of the outer and inner pipes moves in the axial-directional piston mode, the horizontal section of inner pipe behaves like the cantilever, and the elbow acts Hke the hinge. The natural frequency is strongly affected by the axial rigidity of outer supporting pipe. (5)Both effective masses and participation factors were small for particular shell modes.