This document provides an overview of earthquake resistant design for nuclear power plants. It discusses generating design basis ground motions, safety classification and seismic categorization of systems, seismic qualification by analysis and testing, issues with hard rock and soil sites, and concludes that structures, systems and components must be qualified for two levels of earthquakes through analysis, testing or a combination.

1. INDIAN STRUCTURAL INTEGRITY SOCIETY
Workshop on Structural Integrity
Assessment of Nuclear Energy Assets
9th – 10th May 2018
AERB Auditorium, Niyamak Bhavan-B, Mumbai

2. EARTHQUAKE RESISTANT DESIGN
OF
NUCLEAR POWER PLANT
S.M.INGOLE
ASSOCIATE DIRECTOR
(STRESS ANALYSIS & SEISMOLOGY)
NPCIL

3. CONTENT
• Introduction
• DBGM generation
• Safety Class & Seismic categorisation
• Seismic Qualification by Analysis
• Seismic Qualification by Testing
• Issues with hard rock and soil sites on
equipment/piping qualification
• Conclusion

4. Earthquake Resistant Design
• Loss of lives during earthquakes are caused as a secondary
damage due to strong ground shaking resulting into collapse of
buildings, bridges and other man made structures.
• It is therefore, imperative that for earthquake disaster
mitigation, Structure, Equipment & Systems be built to resist
earthquake induced shaking levels during their life time.

5. Damage to Civil Structures

6. Damages to Buildings

7. Tilting of transformer

8. Transformer with wheel arrestor,
wheel support itself bent & got damaged

9. Damage to
Battery bank

10. (Failure of Piping)

11. Piping Failure between jetty no.3 &4 which experienced
Bhuj Earthquake of 26 January2001

12. Safety classification of Systems
Based on contribution of the system to the safety of the nuclear
power plant, systems are classified/graded into
• Safety Class - 1,
• Safety Class - 2
• Safety Class - 3
• The various classes lead to various requirements in material,
fabrication, erection, examination & design.

13. Safety Class 1
The SSCs which are required to perform the safety functions
necessary to prevent the release of a substantial fraction of core
fission product inventory to the containment/ environment eg.
PHT
Safety Class 2
The SSCs that perform the safety function necessary to mitigate the
consequences of an accident which otherwise lead to release of
radioactivity eg. ECCS
Safety Class 3
SSCs required to perform a support role to safety functions in
Safety classes 1 and 2 eg. Process water system
Safety classes

14. 14
Design Requirement for Safety classes
Safety class Design requirements
Safety Class-1 Highest safety class ASME Section III
Div-1, Subsection-NB
Safety Class-2 Less restrictive, Sub-section NC
Safety Class-3 Further less restrictive, Sub-section ND

15. Seismic Categorisation
• Seismic Category-1: Piping and equipment are required to be
qualified for both Operating Basis Earthquake (OBE) and Safe
Shutdown earthquake (SSE). All Safety Class 1, 2 and 3 SSCs
are of Seismic Category-1.
• Seismic Category-2: Piping and equipment are required to be
qualified for S1 (OBE) earthquake only.
• Seismic Category-3: Piping and equipment may be designed
for earthquake resistance as per the national practice for non-
nuclear application.

16. Seismic Qualification of the Structures Systems and
Equipment (SS&E) is done by performing
• By analysis (to demonstrate structural & pressure boundary
integrity)
and/or
• By analysis, testing, combined analysis & testing, experience
based data (to demonstrate operability)
Seismic Qualification

17. Seismic Qualification by Analysis
The dynamic movement during an Earthquake results into
• Stresses
&
• Displacements
in Structures, Systems & Equipment (SS&E)
Resultant stresses in the SS&E for a load combination of DW,
operating loads with earthquake load are used to qualify the SS&E
for the stresses being less than the allowable value (limiting value)
as per the relevant code/standard.

18. Qualification by Analysis
It is possible for SS&E which are passive in nature and which
can be easily modelled by finite element are qualified based
on the stress and displacement as limiting value.
- Pressure vessel
- Piping etc

19. Analysis Methods
Seismic Analysis of SSCs is carried out using following methods
• Response Spectrum Method
• Time History Method
• Equivalent Static Method

20. Response Spectra Method
• Finding out the Frequencies and Mode shapes
• Determination of modal displacements
• Determination of other modal responses (stresses, strains,
forces & moments)
• Determination of final responses incorporating modal and
directional combinations.

21. Steps in Response Spectrum Analysis
1st step: Calculate the mode shapes and frequencies :
This is done by solving the following equation for the eigen vectors and
eigen values
[ [K] - 2
n [M] ] {Øn} = 0
where
[K] - Stiffness Matrix
n - natural frequency of the nth mode
[M] - Mass matrix
Øn - Eigen vector of nth mode
21

22. 2nd Step
Determine the maximum model displacements
This is done as follows:
{Øn}max = PF {Øn} Sa/ n
2
{Øn}max - Max. displacement vector for nth mode
PF - model participation factor for the nth mode given by
- {Øn}T [M] {I} / {Øn}T [M] {Øn}
Sa - acceleration value corresponding to n

23. 3rd Step :
Other responses such as stress, strain, moment, shear can be
calculated from the {Øn} and displacement for each mode in
each orthogonal direction.
4th Step :
Compute the maximum response at a given d.o.f. for all modes
by combining them
• by SRSS/closely spaced modal combination (10% method/CQC
method) for each orthogonal direction
• Combine the directional response by SRSS to get complete
response

24. Missing mass correction
• Missing mass is defined as that mass which has not
participated up to cut-off frequency in the analysis
• The inertial force associated with this missing mass is
significant if the participation is less than 90%.

25. Seismic Anchor Movement Analysis
If the equipment/piping is supported at different floors in a
building or located in different buildings, it will be subjected
to relative displacements at the support points.
• Carry of out SAM (static) analysis applying the relative
displacement at the support points.
• Combine the inertial response (response spectrum analysis)
with SAM response by SRSS to get the total response.

26. Seismic Qualification
• The resulting seismic responses shall be combined with the
responses due to dead weight and other operating load .
• Check the resulting stresses with the codal allowable stresses
for seismic qualification.

27. Seismic Qualification by Analysis
Design and Various Service conditions
Design/Service Levels Loading & Load Combination for Pressure Boundary Components Frequency of
Occurrence
Design Condition Design Pressure, dead weight, sustained loads -
Service Level A*
(Normal Operating Condition)
Operating Pressure & temperature, sustained loads and Process transients
1
Service Level B*
(Upset Condition)
Pressure, dead weight, sustained loads (nozzle loads etc.), OBE (Inertia+SAM) and upset condition
process transients including OBE stress cycles
1 to 10-2
Service Level C
(Emergency Condition)
Pressure, dead weight, sustained loads (nozzle loads etc.) ,SSE loads (Inertia+SAM)##, SSE Stress
Cycles for Fatigue 10-2 to 10-4
Service level D
(Faulted Condition)
Pressure, dead weight, sustained loads (nozzle loads), SSE loads (Inertia+SAM), Pipe rupture loads
(shall not be taken concurrently with SSE)
10-4 to 10-6
Test Condition Dead Weight and Test Pressure
-
Level A: Components must withstand these loads without any damage & no inspection warranted
Level B: Component or support must withstand these loadings without damage requiring repairs.
Level C:
Permits large deformation in the areas of structural discontinuity which may necessitate the removal of the component or support
from service for inspection or repair of damage to the component or support.
Level D:
Permits gross deformation with loss of dimensional stability. Component may be out of service for repairs, which may require
removal of the component or support from service.
* Fatigue Analysis is to be carried out for all process transients under Level-A & Level-B
## SSE shall be considered in Level-C if specified , otherwise it shall be considered in Level-D only

28. Seismic Qualification by Analysis
For Class-I Components For Class-II & Class-III Components
Service
condition
Code
Clause
ASME Section III, Sub-section
NB
Code Compliances
or Protection against various modes of
failure
Allowable stress limit
Design
Condition
NB-3221 Pm < Sm
PL < 1.5 Sm
Pm or PL + Pb< 1.5 Sm
Against bursting and gross distortion from a
single load application (Primary Stress)
Level-A NB-3222 PL+Pb +Q < 3 Sm
PL+Pb +Q+F  Sa,
CUF <1 for Fatigue *
Against progressive distortion from cyclic
application (Primary+Secondary stress),
Low Cycle Fatigue
(Primary+Secondary+Peak Stress)
Level-B NB-3222 PL + Pb+ Q  3 Sm
PL + Pb+ Q +F  Sa,
CUF <1 for Fatigue *
Level-C NB-3224 Pm < Greater of 1.2Sm or Sy
PL < Greater of 1.8Sm or 1.5 Sy
PL + Pb < Greater of 1.8 Sm or
1.5 Sy
Against bursting and gross distortion from a
single load application (Primary Stress)
Level-D Appendix-F
F-1331
Pm <2.4 Sm or 0.7 Su (lesser of)
for Austenitic steel and Pm < 0.7
Su for Ferritic steel
PL < 150% of Pm
Pm+ Pb < 150% of Pm
Nomenclature
Pm =Primary membrane stress intensity
PL = Local primary membrane stress intensity
Pb = Primary bending stress intensity
Q = Secondary stress
F = Peak stress
Sm = Allowable stress intensity of the material
* CUF <1.0 for all transients of Level-A and Level-B considered together
Service
condition
Stress
Limits
Design
Condition/Level-A
σm < 1.0 S
(σm or σL) + σb < 1.5 S
Level-B
σm < 1.10 S
(σm or σL) + σb < 1.65 S
Level-C
σm < 1.5 S
(σm or σL) + σb < 1.8 S
Level-D
σm < 2.0 S
(σm or σL) + σb < 2.4 S

29. Seismic Qualification of Active Mechanical &
Electrical Equipment
• Active Equipment have close gaps & clearances between
moving components
• Closure of gap and clearances can result into a possible
malfunction jeopardizing the functional performance of
the equipment and a seismic qualification by test is
recommended for such equipment for seismic
qualification.

30. List of Active Mechanical Equipment
• Valves
• Rotating equipment
Pumps, fans, blowers, motors
• Reciprocating equipment
compressors, diesel generators,
reciprocating pumps

31. Qualification of Active Mechanical Equipment
• These equipment
have close gaps/clearances between the
moving and stationary components.
viz. Shaft-bearings, impeller-casing, piston-cylinder which
can be modelled and analysed by finite element method to
demonstrate their functional operability.
To demonstrate their functional operability based on
- deflection of moving components being less than the available
gaps and clearances.
- reactions at the bearing being less than the bearing design load.

32. Qualification of Electrical and C&I equipment
Electrical and C&I equipment viz., panels, switchgears, MCCs
etc have
• Relays
• Controllers,
• actuators- spring loaded
• Push button (spring loaded)
• PCBs,
• Transmitters
• recorders
Most of these instruments are small in size, weight and are
delicate.

33. A typical Over voltage Relay Type VTU

34. Another Typical Example of a Relay

35. Issues with instruments/devices
These instruments/devices have
• Close gaps/clearances
• complex geometries
• uncommon materials
– making it difficult to model & analyze and are to be
qualified by testing on a shake table.
– Device Behavior should not disturb the functioning of the
system

36. Shake Table Testing as per IEEE-344
• In general, the shake table test should be conducted by
mounting the equipment on a shake table.
• During the test, the operating loads of the equipment should
be simulated adequately.
• The test should conservatively simulate the seismic event at
the equipment mounting location i.e TRS enveloping RRS
• While a seismic motion is given to the shake table, the
equipment should be checked for its intended functional
operability.

37. Functional Checks
All the functions and the operating parameters and the
state of the devices are
• Prechecked
• Checked during seismic test
• Post checked
for Relay chatter, Relay malfunction, voltage fluctuation,
light indications, door opening, loosening of bolts etc.

38. 0
5
10
15
20
25
0 10 20 30 40
X-axis
0
5
10
15
20
25
0 10 20 30 40
Y-axis
0
1
2
3
4
5
6
7
8
9
0 10 20 30 40
Z-axis
Required Response Spectrum (RRS) & Test Response Spectrum (TRS)
TRS
RRS
Acceleration, m/s2
Frequency, Hz

39. Main Battery Charger

40. Issues with seismic qualification for hard
rock and soil sites
• Spectral peak shifts towards lower side for soil site in
comparison to hard rock site.
• In general, equipment frequencies are higher, as such, the
design will govern by hard rock site.
• Floor displacements are higher for soil site in comparison to
rock site (6-8 times) resulting in higher SAM stresses. Piping
requires additional flexibility within the building and across
the buildings, if going out.
• Low frequency systems requires strengthening eg. Hanging
Cable trays, more free board for sloshing.
• Issue with building Foundation, requires piling.

41. Conclusion
• Structures, Systems and Components are to be qualified for
two levels of earthquakes i.e. OBE & SSE.
• Design Basis ground motion is generated by detailed
geological and seismological studies.
• SSCs are seismically qualified by Analysis, Testing or
combination.

42. Active faults
On the basis of geological, geophysical, geodetic or seismological data, a
fault should be considered active/capable, if the following conditions
apply:
• If it shows evidence of past movement or movements of a recurring
nature within such a period that it is reasonable to conclude that
further movements may occur.
 In highly active areas, where both earthquake data and geological data
consistently reveal short earthquake recurrence intervals, periods of the
order of tens of thousands of years (e.g. Upper Pleistocene–Holocene,
i.e. the present) may be appropriate for the assessment of active faults.
 In less active areas, it is likely that much longer periods (e.g. Pliocene–
Quaternary, i.e. the present) are appropriate.

43. Active faults
• If a structural relationship with a known active fault has been
demonstrated such that movement of the one fault may
cause movement of the other.
• It has generated micro or macro earthquakes.
• If it cannot be established that a fault is not active, the same
shall be considered in the seismotectonic evaluation as active.

44. Safety Class 4
SSCs which incorporate safety functions that do not fall
within safety classes 1, 2 or 3. Safety class 4 includes those
components that are necessary to limit the discharge or
release of radioactive waste and airborne radioactive
material below prescribed limits during all operational
states and would not result in the exposure of the public or
site personnel in excess of prescribed limit, even if they
failed. (e.g., PHT and moderator deuteration and
dedeuteration system, D2O clean up system etc.)
Safety classes

45. 45
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