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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 13625-1992 Seismic qualification of electrical equipment of the safety system for nuclear power plants, and the following main technical changes have been made with respect to GB/T 13625-1992:
—— relevant contents are added for damping (see Clause 6 and Annex A);
—— the requirement is modified for TRS low frequency band so that the low-frequency displacement of the test device shall not be too large (see 8.6.3.2);
—— related contents are added for power spectral density envelope (see 8.6.3.2.1);
—— the seismic qualification approach combining analysis and test is added (see Clause 9);
—— the guidelines for seismic qualification using seismic experience data of reference equipment (see Annex G).
This standard was proposed by China National Nuclear Corporation.
This standard is under the jurisdiction of the National Technical Committee 30 on Nuclear Instruments of Standardization (SAC/TC 30).
The previous edition of this standard is as follows:
——GB/T 13625-1992.
Seismic qualification of safety class electrical equipment for nuclear power plants
1 Scope
This standard specifies the implementation method and documentation requirements of seismic qualification for verifying that safety level electrical equipment can perform its safety function during and/ or after an earthquake.
This standard is applicable to seismic qualification of safety level electrical equipment in nuclear power plants, including any interface components or equipment whose failure will have harmful effects on the performance of safety system.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 12727 Qualification of safety class electrical equipment for nuclear power plants
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply.
3.1
broadband response spectrum
response spectrum that describes motion in which amplified response occurs over a wide (broad) range of frequencies
3.2
coherence function
comparative relationship between two times histories. It provides a statistical estimate of how much two motions are related, as a function of frequency. The numerical range is from zero for unrelated, to +1.0 for related motions
3.3
correlation coefficient function
comparative relationship between two time histories. It provides a statistical estimate of how much two motions are related, as a function of time delay. The numerical range is from zero for unrelated, to +1.0 for related motions
3.4
critical seismic characteristics
design, material, and performance characteristics of an equipment item that provide assurance that the item will perform its required function under seismic loads
3.5
cutoff frequency
frequency in the response spectrum where the ZPA asymptote begins. This is the frequency beyond which the single-degree-of-freedom (SDOF) oscillators exhibit no amplification of motion and indicate the upper limit of the frequency content of the waveform being analyzed
3.6
damping
energy dissipation mechanism that reduces the amplification and broadens the vibratory response in the region of resonance. It is usually expressed as a percentage of critical damping. Critical damping is defined as the least amount of viscous damping that causes a SDOF system to return to its original position without oscillation after initial disturbance.
3.7
earthquake experience spectrum; EES
response spectrum that defines the seismic capacity of a reference equipment class based on earthquake experience data
3.8
flexible equipment
equipment, structures and components whose lowest resonant frequency is less than the cutoff frequency on the response spectrum
3.9
inclusion rules
rules that define the bounds of equipment included in a reference equipment class based on an acceptable range of equipment physical characteristics, dynamic characteristics, and functions for which seismic ruggedness has been demonstrated by experience data
3.10
independent items
components and equipment that (a) have different physical characteristics or (b) experienced different seismic motion characteristics, e.g., different earthquakes, different sites, different buildings, or different orientations/locations in the same building
3.11
narrowband response spectrum
response spectrum that describes the motion in which amplified response occurs over a limited (narrow) range of frequencies
3.12
natural frequency
frequency(s) at which a body vibrates due to its own physical characteristics (mass and stiffness) when the body is distorted in a specific direction and then released
3.13
operating basis earthquake; OBE
earthquake that could reasonably be expected to occur at the plant site during the operating life of the power plant considering the regional and local geology and seismology and specific characteristics of local subsurface material
Note: For the vibratory ground motion produced by the earthquake, those features of the nuclear power plant, necessary for continued operation without undue risk to the health and safety of the public, are designed to remain functional.
3.14
power spectral density; PSD
mean squared amplitude per unit frequency of a waveform, and it is expressed in g2/Hz versus frequency
3.15
prohibited features
design details, materials, construction features, or installation characteristics that have resulted in seismic induced failure or malfunction of the equipment to maintain its structural integrity and perform its specified function at earthquake or test excitations with defined seismic capacity
3.16
qualified life
period of time, prior to the start of a design basis event (DBE), for which the equipment was demonstrated to meet the design requirements for the specified service conditions
3.17
reference equipment
equipment used to establish a reference equipment class
3.18
reference equipment class
a group of equipment sharing common attributes as defined by a set of inclusion rules and prohibited features
3.19
reference site
site containing equipment or items used to establish a reference equipment class
3.20
required response spectrum; RRS
response spectrum issued by the user or the user's agent as part of the specifications for qualification or artificially created to cover future application
3.21
resonant frequency
frequency at which a response peak occurs in a system subjected to forced vibration. This frequency is accompanied by a phase shift of response relative to the excitation
3.22
response spectrum
plot of the maximum response, as a function of oscillator frequency, of an array of SDOF damped oscillators subjected to the same base excitation
3.23
rigid equipment
equipment, structures and components whose lowest resonance frequency is greater than the cutoff frequency on the response spectrum
3.24
safe shutdown earthquake; SSE
earthquake that is based upon an evaluation of the maximum earthquake potential considering the regional and local geology and seismology and specific characteristics of local subsurface material
Note: Some certain structures, systems, and components need to remain their functions under the maximum vibratory ground motion caused by the earthquake. These structures, systems and components are those necessary to ensure the following requirements:
a) Integrity of the reactor coolant pressure boundary;
b) Capability to shut down the reactor and maintain it in a safe shutdown condition;
c) Capability to prevent or mitigate the consequence of off-plant irradiation accidents.
3.25
seismic capacity
highest seismic level for which required adequacy has been verified
3.26
sine beats
continuous sinusoid of one frequency, amplitude modulated by a sinusoid of a lower frequency
3.27
stationarity
condition that exists when a waveform is stationary and when its amplitude distribution, frequency content, and other descriptive parameters are statistically constant with time
3.28
test experience spectra; TES
test-based response spectra that define the seismic capacity of a reference equipment class
3.29
test response spectrum; TRS
response spectrum that is developed from the actual time history of the motion of the shake table
3.30
transfer function
complex frequency response function that defines the dynamic characteristics of constant parameter linear system
Note: For an ideal system, the transfer function is the ratio of the Fourier transform of the output to that of a given input.
3.31
zero period acceleration; ZPA
acceleration level of the high-frequency, unamplified portion of the response spectrum
Note: This acceleration corresponds to the maximum peak acceleration of the time history used to derive the response spectrum.
4 General discussion of earthquake environment and equipment response
4.1 Earthquake environment
Three-dimensional (3D) random ground motion caused by earthquakes may be characterized by simultaneous but statistically independent horizontal and vertical components. The strong motion portion of the earthquake may last from 10 s to 15 s, although the complete event may be considerably longer. The ground motion is typically broadband random and produces potentially damaging effects over a frequency range from 1 Hz to the cutoff frequency of response spectrum.
4.2 Equipment on foundations
The vibratory nature of the ground motion (both horizontal and vertical) can be amplified or attenuated in foundation-mounted equipment. For any given ground motion, the amplification or attenuation depends on the system’s natural frequencies (soil, foundation, and equipment) and the damping dissipation mechanisms. The typical broadband response spectra that describe the ground motion indicate that multiple-frequency excitation predominates.
4.3 Equipment on structures
The ground motion (horizontal and vertical) may be filtered by intervening building structures to produce amplified or attenuated narrowband motions within the structure. The dynamic response of equipment on structures may be further amplified or attenuated to an acceleration level many times more or less than that of the maximum ground acceleration, depending upon the equipment damping and natural frequencies. The narrowband response spectra that typically describe a building floor motion indicate that single-frequency excitation of equipment components can predominate. Similar filtering of in-structure motion may occur in flexible piping systems. For components mounted away from supports, the resultant motion may be predominantly single frequency in nature and centered near or at the resonant frequency of the piping system. This resonance condition may produce the most critical seismic load on components mounted on the line.
4.4 Simulating earthquake
4.4.1 General
The goal of seismic simulation is to reproduce the postulated earthquake environment in a realistic manner. The form of the simulated seismic motion used for the qualification of equipment by analysis or testing can be described by one of the following functions:
a) Response spectrum;
b) Time history;
c) Power spectral density (PSD).
The simulated seismic motion may be generated for the foundation, floor of the building, or substructure upon which the equipment is to be mounted. The simulated seismic motion is usually supplied by the user or the user’s agent as a part of the specifications.
Because of the directional nature of seismic motion and the filtered output motion of building and equipment structures, the directional components of the motion and their application to the equipment shall be specified or accounted for in some other appropriate manner.
4.4.2 Response spectrum
The response spectrum provides information on the maximum response of single-degree-of-freedom (SDOF) oscillators as a function of oscillator frequency and damping when subjected to an input motion. The response spectrum can indicate the frequency content and the peak value of the input motion (namely the ZPA).
It should be pointed out that the response spectrum cannot provide the following information:
a) The waveform or time history of the excitation that produced it;
b) The duration of motion (this shall be defined in the corresponding appraisal technical requirements document);
c) The dynamic response of any specific equipment.
4.4.3 Time history
A time history displays the earthquake-induced motion (usually in terms of acceleration) as a function of time. The simulated motion in seismic qualification test is derived from existing or artificially generated earthquake records. For any floor, the time history generated includes the dynamic filtering and amplification effects of the structures and other intervening support structures.
4.4.4 PSD function
The mean squared amplitude per unit frequency of the vibratory motion is characterized in terms of the PSD as a function of frequency.
Note: Although the response spectrum and the PSD function do not define the exact waveform or duration of the excitation, they are valuable tools. They enable significant frequency-dependent properties of the motion to be seen at a glance from one curve. The PSD provides information regarding the excitation directly without including the effects on an array of SDOF oscillators as is done for the response spectrum. As a result, the PSD allows application of relationships between excitation and response by way of the transfer functions for linear systems.
4.5 Supporting structure and interactions
Seismic qualification of equipment requires consideration of installation features, such as:
a) The seismic adequacy of the supporting structure (supporting assembly, structure, anchorage, floors, walls or foundation);
b) The potential for adverse seismic interactions (such as falling of overhead components, proximity impacts, differential displacements, spray, flood, or fire).
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 General discussion of earthquake environment and equipment response
5 Seismic qualification approach
6 Damping
7 Analysis
8 Testing
9 Combined analysis and testing
10 Experience
11 Documentation
Annex A (Informative) Recommended damping ratio of typical electrical equipment in seismic analysis
Annex B (Informative) Statistically independent motions
Annex C (Informative) Test duration and number of cycles
Annex D (Informative) Fragility testing
Annex E (Informative) Measurement of ZPA
Annex F (Informative) Frequency content and stationarity
Annex G (Informative) Method of seismic qualification with reference to experience data
