Samshin

A nuclear power plant consists of structures, systems, and equipment. Nuclear power plant facilities and equipment are protected from natural environment and disasters. They are designed and manufactured to ensure that they can withstand environmental factors or hypothetical accident conditions and at the same time perform safety-related functions sufficiently.

Boundary conditions

• When thermal deformation and pipe reaction force are considered, the boundary condition (constraint condition) of the valve analysis model completely constrains one side and constrains the other side only in the direction.
• If the valve itself is regarded as a pipe device (part), the boundary condition (constraint condition) of the valve model is completely restrained at both ends.

Assumption

• The analysis assumes constant stiffness and mass without damping to generate the natural frequency of the valve assembly.
• It is assumed that the disk is in the fully open position so that the lowest natural frequency is generated conservatively of the valve assembly.
• In the case of the structure of the mounting flange, it can be regarded as a shear beam, and the shear area is the shear area at the inner thickness of the mounting flange thickness or PCD (Pitch Circle Diameter) bolt hole circle.
• Assume that all welded and bolted parts are perfectly connected.
• In reality, each part consists of various materials, but it is assumed that it is composed of a uniform material (same as the body and bonnet material).
• If shapes that are not the main area of interest can be omitted, the mass of the shapes omitted from the analysis model must be included. It can be applied using the mass element. For example
  • Electric devices such as electric actuators, air actuators, hydraulic actuators, and limit switches
  • Stem
  • Disk
  • Etc

• The mass error between the actual shape (design weight) and the FE Mode must satisfy within 10%.
• Density value and Poisson's ratio used in the seismic verification report are applied as follows.

Interpretation procedure

• 3D modeling work of valves to be used for analysis in Inventor
  
• Conversion of complex parts into mass elements. Validation of modeling
  
• Generate a finite element model by meshing in Ansys Mechanical.
  
• Confirm natural frequency by performing modal analysis to understand the dynamic characteristics of the valve
  
• Perform seismic analysis by applying Design Pressure, Operating Load, Seismic Load (Operating Basis Earthquake (OBE), Safe Shutdown Earthquake (SSE)), etc.
  
• Evaluate the structural integrity of the pressure-retaining parts by calculating the membrane stress + bending stress using the Linearized Stresses method.