APPLICATION OF BASE-ISOLATION TO NUCLEAR
FACILITIES
Pierre Sollogoub
Consultant
(France)
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1
Content
• General idea of base-isolation
• Isolation directions: H, H-V , 3D…
• Isolators
• Non-nuclear applications
• Post earthquake feedback of experience
• Nuclear applications
• Codes and standards
• Some specific questions related to seismic isolation
• Mainly building isolation will be considered in the presentation
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General idea of base isolation
• Low frequency <1Hz
• Accelerations in the
superstructure are decreased
• Displacements are increased
• Higher damping, lower
displacement
• First mode is predominant
(orthogonal to the other modes)
in general
• Limited amplification of
acceleration with height
• In-structure floor response
spectra
• With low frequency peak and
possibly secondary peaks
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a. Acceleration response b. Displacement response
Directions of isolation
• Functions of isolation system:• sustain vertical load
• accommodate displacement : stiffness
• control displacement : damping
• re-centering capacity
• Can be : 1D, 2D, 3D
• Rocking
• …
• Usual: 2 horizontal directions
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Isolators
5
Dampers
Bearing
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Isolators examples
h
D
de
Rubber bearing
Lead-rubber bearing
Friction pendulum bearingFrequency depends only on R:
radius of curvature
Damper
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Isolators
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Hysteretic loop of HDRB (at 110% - left
and 220% - right
GERB Spring and Damper
Spent fuel storage (Switzerland)
Total Supported Weight:
>5000 Metric Tons
Seismic and Airplane Impact !
3D System – « anti-rocking »
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Mechanism of rocking suppression system
Materials
• (Laminated) Rubber
• Natural or Synthetic
• Low Damping Rubber Bearing LDRB
• Lead-Rubber Bearing LRB
• High Damping Rubber BearingHDRB
• Main questions
• Ageing
• Non linear cyclic behaviour
• Ultimate behaviour
• Lead behaviour: cyclic and with time
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Materials
• Sliding devices
• Rigid sliding Bearings
• Curved surface sliders : RECENTRERING CAPABILITY
• Choice of materials:
• Steel surface
• PTFE polytetrafluorethylene
• Main questions:
• Ageing of sliding surface
• Recentering
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Non-nuclear Applications
• The technique is known since beginning of XXth century
(USA and USSR) with few applications
• Derived from bridge devices
• Applied for conventional buildings (70s+): New-Zealand,
Italy, France, Japan , USA…
• Strong development in Japan in late 90s (after Kobe
earthquake – 1995
• Numerous application in industrial facilities: LNG tanks RB,
LRB, FPB
• Emergency buildings in K-K and Fukushima stations
(TEPCO)
11
Seismic feedback of experience
• There are some exemples in California:
• Northridge earthquake 1994– USC Hospital LRB and
LDRB : free field 0.49g- isolated raft: 0.13g – top:0.2g
• Landers Earthquake 1992 – Foothill Communities
Justice Center HDRB: base 0.09g –top 0.19g
• Japan (Kobe 1995, Niigata Chuetsu, 2004, Martinique
(2007)
• Mendoza (Argentina) M5.7 in 2006 2 twin buildings, one
fixes base and one isolated by springs and dampers• Xni/i = 0.25/0.05g
• Yni/i = 0.4/0.06g
• Zni/i = 0.06/0.07g
12
Feedback of experience - Kobe 1995
13
Distorsion of pads during
earthquake: 170mm
Distorsion max: 400mm
LRB and natural rubber
bearings
Seismic feedback of experience
• Great Tohoku earthquake (2011)
• Many base-isolated buildings in Tohoku and
other (Tokyo) region, with acceleration in free-field
up to 0.6g
• Base isolated emergency buildings in
NPPs:Fukushima 1 and 2, Onagawa…
• In all cases, the behaviour was satisfactory, in the
sense that the « filtering » effect was present and
no unexpected phenomena were present. No
damage to structures;Some damages when design
is deficient (on bridges)
• R/D Tests SECED 30/03/2016 London UK 14
Emergency Control Building - BWR
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52.6m
40.6m
52.6m
40.6m
Lead Rubber Bearing(φ1200)[4]
Sliding Bearing[31]
Natural Rubber Bearing(φ1200)[10]
Oil Damper[16]
Design codes and Technical
documents• Conventional buildings
• ASCE/SEI 7-10 Minimum design loads for buildings and other
structures, American Society of Civil Engineers (ASCE), 2010 -USA
• AIJ (AIJ, 2013 Recommendation for the Design of Base Isolated
Buildings, Architectural Institute of Japan, 2013. (in Japanese)
• JSSI (JSSI, 2009, 2012, 2013) Japan Society of Seismic Isolation
developed texts giving list of possible devices, Guidelines for
umbilical’s design and elements on maintenance for buildings and
bridges.
• EN 1998-1:2004 – Eurocode 8: Design of structures for earthquake
resistance – Part 1: General rules, seismic actions and rules for
buildings
• EN 1998-2:2005 – Eurocode 8: Design of structures for earthquake
resistance – Part 2: Bridges
• NF EN 15129:2010 – Anti-Seismic Devices
• NF EN 1337:2005 – Structural bearings
• ISO22762: International Standard is dedicated to elastomeric seismic
isolators16
Design codes and Technical
documents
• Nuclear Facilities• Japan
• JEAG 4614-2013, Seismic Design Guidelines for Base-Isolated
Structures of Nuclear Power Plant, Japan Electric Association,
2013. in Japanese
• JNES, Seismic Safety Division, Proposal of technical review
guidelines for structures with seismic isolation, report n° JNES-RC-
2013-1002.
• Europe
• European Commission, Proposals for design guidelines for
seismically isolated nuclear plants, EUR 16-559 EN, 1995.
• AFCEN PTAN RCC-CW 2015 French Experience and Practice of
Seismically Isolated Nuclear Facilities
• RCC-CW 2015 edition of the AFCEN code for Civil Works17
Design codes and Technical
documents
• USA
• U.S. Nuclear Regulatory Commission (USNRC) NUREG/CR xx,
Technical considerations for Seismic Isolation of Nuclear Facilities,
Draft May 2013
• ASCE Standard, ASCE 4-xx Seismic Analysis of Safety-Related
Nuclear Structures and Commentary. ASCE, 20xx
• ASCE Standard, ASCE 43-05, Seismic design criteria for SSC in
Nuclear Facilitiies, ASCE, 2005 (under revision)
• IAEA:
• TECDOC 1288 Verification of analysis methods for predicting the
behaviour of seismically isolated nuclear structures (CRP 1996-
1999)
• TECDOC (Draft) Seismic Isolation systems for Nuclear Installations
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Design codes and Technical
documents
• OTHER documents
• France: Technical specifications used for RJH and
ITER design
• USA
• PEER and MCEER reports
• EPRI Draft on Seismic Isolation for NPP
• AASHTO document for bridges
• Korea
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Nuclear ApplicationsAdvantages
• Lower accelerations on structures and components, enabling simple,
seismically safer, economical and standardised design
• Simple structural behaviour leading to a simplicity of the analyses – in
some cases, static analysis may be applicable for equipment inside
isolated structure.
• Increase safety by decreasing in the uncertainties, due to the fact that
the “critical” element is the seismic isolation system itself, for which the
behaviour up to failure is better evaluated than the one of a non-
isolated structure.
• Simpler layout, with possibly more slender buildings and more flexibility
to locate equipment (for instance, due to almost constant acceleration
over height, it is possible to have heavy or sensitive components
located at higher elevations),
• Reduce costs for new build (in terms of scheduling and global price)
due to the capability to reuse original design for middle range seismic
input (typically 0.25-0.3g) and existing main components qualificationSECED 30/03/2016 London UK 20
Why so few application of BI in
Nuclear facilities?
• Licensing: BI is a « NEW » technique
• Construction schedule is increased
• Cost of isolation system and complementary raft;
must be compensated by lower cost of SSCs
• Lack of consensus standards
• Nuclear Market in high seismicity zones
• Cost-benefit analysis has to be done; from which
value of acceleration is BI interesting?
• Lack of audacity!
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Nuclear projects (partial)
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Facility Country Type Date
EFR Europe FBR 80s
PRISM USA Small WR Mid 80s
SAFR USA Fast Reactor Mid 80s
KALIMER Korea Fast Reactor
ALMR USA Fast Reactor
STAR-LM USA LMR Gen IV
IRIS International 2000s
SILER Europe GEN IV reactors 2012
ASTRID Europe/
France
GEN-IV SFR Under develop.
ALFRED Europe/
Romania
GEN IV LCFR Under develop.
Some Nuclear Projects
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IRIS
STAR -LM 3D isolation
PRISM
KALIMER
ASTRID ALFRED
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GEN IV – SFR
France
GEN IV LCFR
Romania
French Base Isolated Nuclear Installations
• CRUAS 900MWe NPP (EDF)
• KOEBERG 900MWe NPP (RSA)
• La Hague storage pools (COGEMA)
• STAR Laboratory in CADARACHE (CEA)
• Georges Besse II enrichment plant
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CRUAS NPP
• Facility: Nuclear Power Plant – 4 Units (900MWe) EDF (1980)
• Location: CRUAS in the Rhone valley
• The plant is part of a standardised set designed to 0.2g; presence of a shallow focus 0.3g earthquake
• Two twin units Nuclear Island (raft dimensions: 140m x 80m) 300000tons on 2000 pads
• Pads: laminated rubber bearings ; 0.5m x 0.5m x 0.065m (3 neoprene layers 13.5mm thick)
• Neoprene Rubber
• Isolation frequency: 1Hz (the objective was to limit the acceleration to 0.2g, with 5% damping)
• Possibility of pads replacement (qualified in-situ procedure)
• Koeberg NPP (South-Africa), same type of bearings with slidingplate
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Cruas – Seismic input
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0.01
0.1
1
0.1 1 10 100
Accele
rati
on
(g
)
Frequency (Hz)
SDD EDF 0.2g
SDD CRUAS 0.3g
CRUAS - Position of pedestals
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CRUAS NPP
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Cruas NPP
Courtesy EDF
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Design
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Eigenfrequency of the isolated structure
It is a trade-off between effects on acceleration and on differential
displacements.
At Cruas-Meysse f0 = 1Hz was selected , resulting in a 5 cm differential
displacement.
Main technical features
Shear modulus G0: 1.1 GPa
Damping : 7%
Pressure on isolation pads: 7.5 MPa
Rubber thickness: 40.5 mm
Distortion under SSE: 1.2
(shear strain : 120%)
Ageing effects on G
Anticipated : G0 x1.3 after 20 years ; < G0 x1.5 after 60 years
Design margin: G0 x 2.25 (the design is still OK up to f = f0 x1.5)
Design
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Laminated polychloroprene rubber
bearings
In 1978, in France, elastomer bearings
pad had been used for 30 years, with an
excellent experience feedback.
In Europe, around 50 000 road or rail
bridges are placed on such pads.
KOEBERG NPP
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Construction Lower raft and pedestals (31-12-1977) Photo: Spie Batignolles
Koeberg (RSA) NPP
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PGA: 0.3 g
Frequency: 0.75 Hz
Pad size: 700x700x130 mm
G modulus: 1.4 Mpa
Friction coefficient: 0.2
JHR General Design
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RJH Seismic Design
• Use of industrially proven solution : square elastomere pads
• Low damping
• Frequency : 0,65 Hz at the end of life
• Dimensions of pads : 0,9 x 0,9 m2
• Design compressive stress 7,5 MPa
• Maximum design distorsion : 1,4
• 211 Pads
- Review of existing standards: EC8, AFPS90, SETRA Guidelines…
• Ageing is taken into account by considering a margin in ShearModulus
• Integration of inspection constraints
- Accessibility
- Testing
• Integration of pads replacement capability
• Equipment design: margins
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ITER International Thermonuclear Experimental Reactor
Under construction
PGA: 0.32 g
Frequency: 0.55 Hz
Pad size: 900x900x181 mm
G modulus: 1.1 Mpa
Same isolators than RJH
RJH ITER
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ITER JHR
Elastomeric
bearing
characteristics
900x900x181 mm square bearing
6 layers of 20mm of elastomer
5x 5 mm-thick steel plates + 2 external 15
mm-thick steel plates
Mechanical
properties
Dynamic shear modulus: Gd = 1.1 MPa
Damping : 5%
Shape factor S 11.25
PGA (hard soil)
Number of
isolators493 195
Mass (t) ~ 300 000 ~110 000
Isolation
frequency (Hz)0.55 0.6
Service loading
(NSd)6.4 MN (s = 8 MPa) 5.67 MN (σ = 7 MPa)
Displacement dbd
(mm)112 108
Georges Besse II enrichment plant
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Seismic spectrum of TRICASTIN
0,0010
0,0100
0,1000
1,0000
0,10 1,00 10,00 100,00
Frequency (hz)
Acc
ele
rati
on
(g
)
SMS 5%
IPS2 5%
GBII
Elastomeric
bearing
characteristics
Circular bearing of diameter 500mm
Height around 400mm
Mechanical
properties
Dynamic shear modulus: Gd = 0.7 MPa,
Damping : 7 %
PGA 0.3g
Displacement dbd
(mm)100
Facility isolated for protection of the
investment considerations
Some specific questions related to seismic
isolation
• Design of Isolators – Manufacturing - Material – Qualification –Ageing - monitoring
• Input signal (low frequency)
• Isolator(s) replacement
• Construction tolerances (on site)
• Control of vertical loads on isolators• Construction phasing
• Vertical stiffness of isolators
• Tension loads / uplift
• Other external events: fire, aircraft crash…
• Connecting structures – umbilicals
• Effect of isolators damping
• Non-linear isolator behaviour – H and V coupling
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Cruas- replacement
of 2 isolators
Some specific questions
• Ultimate behaviour of the isolation system
• Margins
• Beyond design conditions
• PRA
• Hard stop or not – moat design
• Ductility demand
• Signal on isolated part has a « low frequency » content. Ductility
demand may be important.
• A complementary margin above calculated response spectrum is
necessary
• In structure Response Spectra
• Equipment design
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Inelastic Spectra – RG1.60 spectrum
Frequency
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Elastic
Duct. 2.0
Duct. 3.0
Duct. 5.0
Elastic
Frequency [Hz]
333231302928272625242322212019181716151413121110987654321
Response A
ccele
ratio
n [g]
3,4
3,2
3
2,8
2,6
2,4
2,2
2
1,8
1,6
1,4
1,2
1
0,8
0,6
0,4
0,2
0
Base Isolated Structure inelatic FRS
Frequency
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Elastic
Duct. 2.0
Duct. 3.0
Duct. 5.0
Elastic
Frequency [Hz]
5048464442403836343230282624222018161412108642
Response A
ccele
ratio
n [g]
6
5,5
5
4,5
4
3,5
3
2,5
2
1,5
1
0,5
0
Example: ITER
(fusion experimental
reactor) [Combesure et al, 2010]
Horizontal floor spectra
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In Structure Response Spectra
In-structure Response spectra
• Secondary peak may be due to:
• Vertical – Horizontal coupling
• Kinematic interaction in embedded foundations
• Damping in the isolation system
« Simple » dynamic behaviour is no more applicable
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Equipment behaviour
SILER International Workshop, 18-19 June
2013, Roma
46
10-1
100
101
102
100
101
102
fréquence (Hz)
spectre pseudo-accélération m/s2
RCC-E
SQUG
BI structure
Conclusions
• There are many techniques for base isolation
• Manufacturing quality, ensure a good long term
behaviour
• Good behaviour of base isolated structures
during earthquakes
• There are examples of base-isolated nuclear
facilities
• Some care must be exercised in design
• Seismic isolation is a mature technique for
nuclear facilities
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