Page 1 (13)
TECHNICAL REQUIREMENTS FOR ELECTRICAL EQUIPMENT
Title
Document
Environmental specification for seismic conditions
TBE 102:2
Issue
4 (E)
Contents
1
1.1
1.2
1.3
1.4
2
3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
3.11
Document
GENERAL.......................................................................................... 2
Background......................................................................................... 2
Basic objectives regarding seismic capability .................................... 2
New design or replacement of equipment .......................................... 3
Applicable standards and regulations ................................................. 3
DEFINITIONS.................................................................................... 3
ENVIRONMENTAL CONDITIONS ................................................ 4
General ............................................................................................... 4
Design seismic environment............................................................... 5
Response spectra ................................................................................ 5
Seismic environmental classes for Forsmark 3 and
Oskarshamn 3 (F3/O3) ....................................................................... 6
Seismic environmental classes for other units.................................... 6
Damping ............................................................................................. 7
Ground Response Spectra................................................................... 8
Example of relationship between ground response, floor
response and response for installed equipment .................................. 10
Seismic environmental classes - 4 % damping................................... 11
Seismic environmental classes - 5 % damping................................... 12
Seismic environmental classes - 7 % damping................................... 13
Issue
TBE 102:2
Date
4 (E)
Supersedes
2013-08-20
Issue 3 (E)
TBE 102:2
Issue 4 (E)
Page 2 (13)
1
GENERAL
These Technical Requirements provide guidelines on how to specify and interpret
seismic requirements for electrical equipment to be used in Swedish nuclear power
plants.
1.1
Background
The first nuclear power plants in Sweden initially were designed with no seismic requirements. A general robust design was considered to provide adequate protection
against seismic events. As a result of more stringent safety rules issued after the
construction, requirements on the ability to withstand earthquakes have been added.
For the two latest reactors, Forsmark 3 and Oskarshamn 3, (F3/O3), seismic
requirements according to American regulations have been applied for design and
construction.
Later, in a jointly project between SSM (Swedish Radiation Safety Authority) and the
Swedish utilities in 1985-1989 a characterisation of earthquakes was defined, including ground response spectra with frequency content and duration applicable to
Swedish conditions. Ground response spectra were developed for frequencies of
1E-5/year, 1E-6/year and 1E-7/year. See section 3.7, Figure 1.
The frequencies 1E-5/year and 1E-7/year have been selected as requirements for the
evaluation of the safe shut down and cooling of the reactor and the reactor
containment integrity respectively.
During the continued evaluation of the seismic capabilities of the plants performed
by the Swedish utilities, problems have been identified as the specific Swedish response spectra has higher acceleration levels than the corresponding American spectra for frequencies above 10 Hz. This means that international experience and test results cannot be applied directly to the Swedish conditions. Especially for electrical
equipment, such as relays and contactors, which are sensitive to frequencies above
ca 33 Hz it has been difficult to analyse and to verify their capability and function,
since no international studies for this type of equipment have been made for these
higher frequencies.
In order to verify seismic capability for the older nuclear power plants the following
objectives have been outlined.
1.2
Basic objectives regarding seismic capability
Structures and components of essential importance for the safe shutdown and long
term core cooling of the reactor must have a seismic capability sufficient for the
seismic loads which can be expected at the frequency of 1E-5/year per unit. This
requirement also applies to seismic interaction, which means that structures, piping
or equipment not required to be seismically qualified must not cause damage to
equipment that are required for safe shut down during an earthquake.
As examples of seismic interaction requirements the structures, piping, or equipment
must not loosen, burn, explode, cause short circuits, etc, during an earthquake.
TBE 102:2
1.3
Issue 4 (E)
Page 3 (13)
New design or replacement of equipment
For new design or replacement of component type (but not necessarily for repair of
excisting seismically qualified equipment) the guidelines in these Technical Requirements must be followed. Applicable seismic requirements are to be specified in
the Technical Specification.
These requirements shall include specific required response spectra or response
spectra selected according to section 3.4 and 3.5. In the latter case response spectra
according to seismic environmental class SL1-SL6 shall envelop specific required
response spectra.
1.4
Applicable standards and regulations
IEC 60980
Recommended practices for seismic qualification of electrical equipment of the
safety system for nuclear generating stations.
IEEE Std 344
Recommended Practices for Seismic Qualification of Class 1E Equipment for
Nuclear Power Generating Stations.
Other equivalent standards and regulations may be used after approval by the
Purchaser.
2
DEFINITIONS
Frequency
In this document frequency has two completely different meanings:
1) Occurrence frequency is given the unit 1/year. The occurrence frequency is the
inverse of the statistical mean time between earthquakes for a nuclear facility
with maximum ground acceleration (PGA) exceeding a certain value.
2) The frequency content expressed in Hz for the actual earthquakes.
Seismic loads
In this document acceleration forces are expressed with the unit m/s2 or g, where
1 g = 9,81 m/s2.
Damping
Damping is the generic name used for energy dissipation, which reduce the forces
and duration of the motions in mechanically oscillating systems. Damping occurs
primarily due to friction in mechanical joints and permanent deformation of structural materials. Damping is expressed as percent of critical damping, which means
that the next coming motion has x % less energy content than the previous motion.
Common damping values are 2-10 %.
Node
Node means the location in a building for which a response spectrum is generated.
TBE 102:2
Issue 4 (E)
Page 4 (13)
PGA (Peak Ground Acceleration)
See definition of ZPA.
Response spectrum
A response spectrum is a diagram showing maximum response, e.g. in the form of
displacement, velocity or acceleration acting on all single degree of freedom systems,
caused by an applied motion (e.g. ground motions or building motions). Normally a
response spectrum is expressed for a given damping. The damping applies to a
certain affected oscillating system (installed equipment), when placed in the node for
which the response spectrum is generated. Example of response spectra is shown in
section 3.8. Response spectra are defined for the two horizontal axes x-, y- and
vertical z. For F3/O3 normally no distinction is made between response spectra for
the x– and y– axes. For the older nuclear units, which were not designed for seismic
influences, big differences in response spectra for x-, and y– axes may exist.
Normally one enveloping response spectrum for of the two axes x- and y- is
considered.
Time History
A diagram, with the unit “time” on the x-axis, and “acceleration” on the y-axis, describing the design basis ground motion. Section 3.7, Figure 2, shows a time history
for the ground motion. A time history may also be calculated for a certain level in a
building, including dynamic filter and amplification factors for the building and other
influencing structural elements.
ZPA (Zero Period Acceleration)
Acceleration level of the high frequencies in the part of the response spectrum where
no amplification effects occur. At increasing frequency the response curve flattens
out asymptotically to the ZPA level. ZPA is the maximum applied acceleration and
corresponds to the maximum peak value of the time history used to derive the response spectrum. The higher acceleration levels of the response spectrum are caused
by resonance phenomena in the affected systems. For ground acceleration the
designation PGA (Peak Ground Acceleration) is often used instead of ZPA. Section
3.8 shows examples of response spectra with ZPA levels indicated.
3
ENVIRONMENTAL CONDITIONS
This section gives basic information about the seismic loads that buildings and
equipment are subjected to. Verification requirements for equipment with seismic
requirements are specified in KBE EP-147.
3.1
General
An earthquake causes both horizontal and vertical ground motions. These motions
are similar to random noise having the frequency content mainly below 50 Hz. The
duration of a major Swedish earthquake is about 10 seconds. See time history diagram in section 3.7, Figure 2.
TBE 102:2
3.2
Issue 4 (E)
Page 5 (13)
Design seismic environment
For Swedish nuclear power plants the so called S1 Earthquake according to
IEC 60980 or OBE Operating Basic Earthquake according to American regulations
(with the frequency 1E-2/year) need not to be considered. This means an earthquake
expected to occur during the operating life of the plants.
On the other hand S2 Earthquake according to IEC 60980 or SSE Safe Shutdown
Earthquake according to American regulations has to be considered.
This means that for seismic loads which can occur with an average frequency greater
than 1E-5/year and unit necessary safety functions must be demonstrated to fulfil the
intended functions.
The ground motions specified for Swedish nuclear power plants are shown in section
3.7, Figure 1.
For F3/O3 the curve based on Regulatory Guide 1.60, but modified for
PGA = 0,15 g horizontal acceleration, applies.
3.3
Response spectra
Based on the given ground response spectra in section 3.7, Figure 1, the relevant
floor response spectra are generated for the node (location) where the electrical
equipment is to be placed.
Applicable horizontal and vertical response spectra are given in the Technical Specification. In an early stage of design or purchase the damping for the actual electrical
equipment may not be known. Therefore, the response spectra for the node should be
generated for a number of different damping values. See also section 3.6.
In order to avoid that a large number of response spectra are called for during design
or purchase of electrical equipment, a simplification may be made to allow for verification according to a seismic environmental class shown in this document. Hence the
seismic environmental class becomes the requirement level that is verified by testing
according to KBE EP-147.
When using this type of broadened response spectra it should be noted that the
applied energy is proportional to the square root of the bandwidth. This implies that
equipment withstanding each single response spectrum may not withstand the applied
energy when tested with a broadened response spectrum making up an envelope of
the single response spectra.
TBE 102:2
3.4
Issue 4 (E)
Page 6 (13)
Seismic environmental classes for Forsmark 3 and Oskarshamn 3 (F3/O3)
F3/O3 are designed for horizontal ground motion with PGA = 0,15 g.
See section 3.7, Figure 1. Vertical ground motion is assumed to 2/3 of the horizontal.
For F3/O3 there are stereotyped response spectra based on which height in the
building the equipment is located and depending on how the equipment is mounted.
There are three seismic environmental classes defined, class 3, 4 and 5. For class 3
and 4 the response spectra are given for horizontal and vertical acceleration respectively. For class 5 no specific response spectra have been given. The combined
building responses are calculated according to Regulatory Guide 1.92, Rev 1.
For equipment mounted directly on walls or floors, current requirements specify
response spectra according to seismic environmental class SL1 or SL2. For
equipment mounted on other structures class SL5 applies. See Table 1 below.
Seismic environmental class, applicable for F3/O3 only
Seismic
Equipment location
Replaces
Environearlier class
mental
Class
SL1
Equipment mounted directly to building structure, Class 3
0-8 m above ground
SL2
Equipment mounted directly to building structure, Class 4
8-20 m above ground
SL5
Equipment mounted on e.g pipes, ventilation
Class 5
drums, cable raceways or other structures
Table 1
Response spectra for seismic environmental classes shown above are given in section
3.9, 3.10 and 3.11.
3.5
Seismic environmental classes for other units
For other units initially not designed for earthquakes, it is not permitted to use the
F3/O3 stereotyped classification.
For each equipment required response spectra must be generated for the equipment
mounting position. When the required response spectra have been generated for both
horizontal and vertical acceleration, one response spectrum shall be selected enveloping all horizontal and vertical required response spectra for the actual positions.
For equipment which can be expected to be used in a number of mounting positions
or buildings, the response spectrum is to be selected so that the qualification becomes
valid for all these positions and buildings. Primarily the response spectra are to be
selected from the seismic environmental classes SL1–SL6. In these classes the
response spectra curves are defined for the damping 4 %, 5 % and 7 %. The damping
value of the test spectrum shall not be higher than the lowest damping value of the
actual equipment.
For alternative damping values use IEC 60980 to determine amplification factor
(ratio between strong part and ZPA) at different damping values for a typical “timehistory”.
TBE 102:2
Issue 4 (E)
Page 7 (13)
The classes SL1–SL6 make no distinction between vertical and horizontal acceleration with respect to the test spectrum that is to be used.
If no broadened response spectrum according to class SL1–SL6 envelopes actual
spectra for specific mounting positions, or if the broadened spectrum is considered
too conservative, then the horizontal and vertical spectra for specific mounting
positions could be used instead as required response spectra.
Seismic environmental class, applicable to all units except F3/O3
Seismic
Equipment location
Comment
Environmental
Class
SL1
Equipment mounted directly to
Response spectra based on
building structure
calculated maximum building
response spectra
SL2
-"-"SL3
-"-"SL4
-"-"SL5
Lowest class for equipment
Response spectra based on
mounted on e.g. pipes, ventilation calculated maximum response
ducts, cable raceways or other
spectra for structures
installed structures
SL6
Equipment mounted on e.g.
-"–
pipes, ventilation ducts, cable
raceways or other installed
structures
Table 2
Response spectra for seismic environmental classes shown above are given in section
3.9, 3.10 and 3.11.
3.6
Damping
Damping values for verification by test or analysis are to be selected according to
approved standard, e.g. those referred to in section 1.4, or according to documented
recognised practice.
If damping values can not be established 5 % must be used.
TBE 102:2
3.7
Issue 4 (E)
Page 8 (13)
Ground Response Spectra
Figure 1
The broken line in the diagram represents the F3/O3 design requirements for a
ground response spectrum, based on Regulatory Guide 1.60, modified for PGA =
0,15 g horizontal acceleration. The other curves represent later defined design criteria
for ground response spectra, based on specific swedish conditions, with the
frequencies 1E-5/year, 1E-6/year and 1E-7/year.
All curves represent 5% damping.
TBE 102:2
Figure 2
Illustration of a swedish earthquake
Issue 4 (E)
Page 9 (13)
TBE 102:2
3.8
Issue 4 (E)
Page 10 (13)
Example of relationship between ground response, floor response and response
for installed equipment
Cubicle Response
Floor Response
Ground Response
Example of repeated response spectra calculations. The ground response spectrum,
which is characterised by the local geological conditions, is amplified in the building
resulting in a floor response spectrum. A cabinet for electrical equipment is placed on
the floor. The cabinet contains electronics and other electrical components. The floor
response spectrum is amplified by the cabinet to a new response spectrum for a
specific position in the cabinet. The ground response spectrum in this case is for 5 %
damping at a maximum ground acceleration of 1,5 m/s2 and is used for analysis of
buildings. The floor response spectrum in this case is for 4 % damping at the
maximum floor acceleration of 5,5 m/s2.
The cabinet is exposed to an acceleration characterised by the floor response spectrum. A position in the cabinet give accelerations designated “Skåprespons” in the
response spectrum, in this case calculated for 5 % damping. The maximum acceleration is 8,0 m/s2. The cabinet has a resonance frequency at 24 Hz, which gives
acceleration values of 36 m/s2.
The cabinet response spectrum according to the diagram illustrates the effect on affected components (single degree of freedom models with 5 % damping) in the analysed position in the cabinet. If the affected component has a resonance frequency at
11 Hz, we read the acceleration 19 m/s2, but if the resonance frequency is 15 Hz, we
read 36 m/s2. These accelerations are the result of a ground motion as shown in
section 3.7, Figure 2.
TBE 102:2
3.9
Issue 4 (E)
Page 11 (13)
Seismic environmental classes - 4 % damping
g
12
SL6
11
10
9
SL5
8
7
SL4
6
5
SL3
4
SL2
3
SL1
2
1
Hz
0
1
Hz
1
1,6
3
4
25
50
60
10
SL1
g
0,1
0,4
1,7
2,3
2,3
0,4
0,4
SL2
g
0,2
1,3
2,8
2,8
2,8
0,7
0,7
SL3
g
0,2
1,6
3,4
3,9
3,9
1,1
1,1
100
SL4
g
0,3
2,0
4,2
6,0
6,0
1,7
1,7
SL5
g
0,4
2,7
6,0
7,5
7,5
3,0
3,0
SL6
g
0,4
3,5
7,8
11,2
11,2
3,2
3,2
TBE 102:2
3.10
Issue 4 (E)
Page 12 (13)
Seismic environmental classes - 5 % damping
g
12
11
SL6
10
9
8
SL5
7
6
SL4
5
4
SL3
3
SL2
2
SL1
1
Hz
0
1
10
Hz
1
1,6
3
4
25
50
60
SL1
g
0,1
0,4
1,5
2,1
2,1
0,4
0,4
SL2
g
0,2
1,2
2,5
2,5
2,5
0,7
0,7
100
SL3
g
0,2
1,6
3,4
3,4
3,4
1,1
1,1
SL4
g
0,3
2,0
4,2
5,2
5,2
1,7
1,7
SL5
g
0,4
2,7
5,5
6,8
6,8
3.0
3.0
SL6
g
0,4
3,5
7,8
9,9
9,9
3,2
3,2
TBE 102:2
3.11
Issue 4 (E)
Page 13 (13)
Seismic environmental classes - 7 % damping
g
12
11
10
SL6
9
8
7
SL5
6
SL4
5
4
SL3
3
SL2
2
SL1
1
Hz
0
1
10
Hz
1
1,6
3
4
25
50
60
SL1
g
0,1
0,4
1,4
1,84
1,84
0,4
0,4
SL2
g
0,2
1,1
2,24
2,24
2,24
0,7
0,7
100
SL3
g
0,2
1,6
3,0
3,0
3,0
1,1
1,1
SL4
g
0,3
2,0
4,2
4,6
4,6
1,7
1,7
SL5
g
0,4
2,4
4,9
6,0
6,0
3,0
3,0
SL6
g
0,4
3,5
7,8
8,6
8,6
3,2
3,2