Background
Fauske & Associates, LLC (FAI) provides critical support to nuclear equipment manufacturers and suppliers, OEMs and utilities with a range of services and testing designed to qualify equipment, parts and components for many applications. These include both mild and harsh nuclear environments to NRC guidelines and to meet industry and plant-specific requirements.
Our material testing laboratory is also equipped with instruments including a Fourier Transform Infrared (FTIR) Spectrometer utilized for various applications related to Material Forensics and Identification testing to identify what the component material is and to perform forensics. Additionally, aged materials can be evaluated to determine the response of the material as a result of the environment conditions.
Material Performance testing is delivered using our INSTRON material property test rig which is able to perform industry standard tests including tensile strength and strain to determine mechanical properties of components.
Background
Class 1E equipment for nuclear power generating stations is safety related equipment that is essential for safe shut down of the reactor. It has to be safe in case of seismic activity. In other words, it must be assured that the equipment performs as designed during and after a seismic event. A qualification that guarantees this can be obtained by testing the equipment on a seismic shake table. The qualification can be obtained by following IEEE (Institute of Electrical and Electronics Engineers) standard 344, which containes the recommended practices for seismic qualification of class 1E equipment for nuclear power generating stations. The practices should be used to ensure that the equipment can meet its performance requirements during and following one safe shutdown earthquake.
Vibrating Systems
Fundamental knowledge of mechanical vibrations is required when analyzing the effects of a seismic event on plant equipment. The following is a brief review of vibration theory:
Figure 1
Figure 1 can be understood as a simplified schematic of a plant component, such as a pump or an electrical cabinet, mounted to the ground. During an earthquake, the ground undergoes motion, which is called base excitation. Depending on the stiffness, mass and damping characteristic of the component, the equipment will undergo a vibratory motion (response). The response can be violent if the frequency of the base excitation coincides with one of the natural frequencies of the component. This is called resonance. A resonance situation is to be avoided at all times. A seismic event consists of an irregular time history of base displacements. However, it typically covers a certain frequency range, which is based on the geographical location of the site. Consequently, the component should be designed in a way that it does not exhibit any natural frequencies in the range of the expected earthquake frequencies. Damping can dissipate some of the energy of the vibratory response. Additional damping by dashpots or frictional plants can be an option if the natural frequency cannot be sufficiently designed “away”.
Seismic Testing
The equipment to be tested is mounted in a plant typical arrangement to the table. Before any testing, the equipment should be checked for functionality. Once the functionality is assured, either a sine sweep resonance search or a multi frequency random noise excitation is conducted to detect the natural frequencies of the equipment. This is also done to demonstrate that the mounting configuration is sufficiently rigid. For that activity the equipment is typically instrumented with a sufficient number of accelerometers. The equipment will then undergo five (5) Operating Basis Earthquake (OBE) and finally one (1) Safe Shutdown Earthquake (SSE) profiles. The Required Response Spectra (RRS) for these tests constitute a requirement to be met by the shake table time history motion. The RRS are predetermined by analysis and entered into the controller of the seismic table. They depend on various factors such as the location, the building and the bedrock. During the test, the accelerometers are used to record the Test Response Spectra (TRS). The TRS must exceed or envelope the RRS, which is typically shown by overlaid plots. The equipment shall be in operational mode during the tests and monitored for performance. A post test functionality check shall also be performed. If the equipment performs well, is free of material failures, structurally intact and the TRS exceeded the requirement, then the equipment can be classified as Class 1E. Figure 2 is a photograph of a component that was tested on a seismic shake table.
It is important to note that the IEEE 344 standard includes further practices than presented here. The presented is one example of how to obtain seismic Class 1E qualification.
Figure 2
