pplication of base-isolation to uclear facilities

APPLICATION OF BASE-ISOLATION TO NUCLEAR

FACILITIES

Pierre Sollogoub

Consultant

(France)

SECED 30/03/2016 London UK

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

SECED 30/03/2016 London UK2

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

SECED 30/03/2016 London UK 3

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


Isolators

5

Dampers

Bearing


Isolators examples

h

D

de

Rubber bearing

Lead-rubber bearing

Friction pendulum bearingFrequency depends only on R:

radius of curvature

Damper


Isolators


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 »


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


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


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


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


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


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



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


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!


Nuclear projects (partial)


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


IRIS

STAR -LM 3D isolation

PRISM

KALIMER

ASTRID ALFRED


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


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


Cruas – Seismic input


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


CRUAS NPP


Cruas NPP

Courtesy EDF


Design


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


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


Construction Lower raft and pedestals (31-12-1977) Photo: Spie Batignolles

Koeberg (RSA) NPP


PGA: 0.3 g

Frequency: 0.75 Hz

Pad size: 700x700x130 mm

G modulus: 1.4 Mpa

Friction coefficient: 0.2

JHR General Design


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



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


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


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


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


Inelastic Spectra – RG1.60 spectrum

Frequency


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


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


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


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


pplication of base-isolation to uclear facilities

Documents