french experience and practice of seismically isolated ... experience... · will be published by...

| 1SILER International Workshop – 2013/06/18-19 – Rome

French experience and practice of seismically isolated nuclear facilities – Main considerations

1 NUVIA Travaux Spéciaux, Lyon, France

2 EDF Nuclear Engineering Division SEPTEN, Lyon, France

3 AREVA Engineering & Projects, Lyon, France

Sébastien DIAZ & Micaël CONNESSON1, Frédéric ALLAIN2, Nadim MOUSSALLAM3, Ilie PETRE-LAZAR2


Introduction

Since recent events in KK and FKS, there is a global renewal of interest in seismic isolation technologies.The IAEA is preparing a TECDOC dedicated to the seismic isolation of nuclear facilities.For more than 30 years, seismic isolation technologies have beenused by operators of nuclear facilities in France (EDF, AREVA, CEA, I/O) to protect them against earthquake loading.To support the IAEA documentation effort and to share knowledge with other member countries, a synthesis of the French practice and experience is being jointly written by operators, designers and manufacturers.This presentation is an extract from this work. The full document will be published by AFCEN before the end of 2013.

Le Groupe NuviaFrench practical examples of isolated NPP 1ActivitésIsolated plant overview 2Gamme de produitsPlant design 3Exemples de projetsIsolators design & technological choice 4Exemples de projetsEquipments design 5

| 3SILER International Workshop – 2013/06/18-19 – Rome3


Cruas NPP

4 PWR 900 Mwe units,EDF, Cruas, France

CruasNPP

Dynamic shear modulus: Gd = 1.1 MPa ± 0.10 MPa,Damping : 7.5 ± 1%

Shape factor S 9.26PGA 0.3 gIsolation frequency (Hz) 1Displacement dbd (mm) 48

Elastomeric bearing characteristics

Mechanical properties

500 x 500 x 66.5 mm square bearing 3 layers of 13.5 mm of elastomer 2 x 3 mm-thick steel plates + 2

external 10 mm-thick steel plates

1

courtesy of EDF


Cruas NPP 1

courtesy of EDF


La Hague Spent Fuel Storage Pools

Spent Fuel Storage PoolsAreva, La Hague, France

La Hague700 x 700 x 147 mm square bearing10 layers of 10 mm of elastomer9x 3 mm-thick steel plates + 2 external 10 mm-thick steel platesDynamic shear modulus: Gd = 1.1 MPaDamping : 7%

Shape factor S 17.5PGA 0.2gIsolation frequency (Hz) 0.85Displacement dbd (mm) 120 (including torsion motion)



1

courtesy of AREVA


Jules Horowitz Reactor

Experimental and medical research-dedicated reactorCEA, Cadarache, France

JHR900x900x181 mm square bearing6 layers of 20 mm of elastomer5x 5 mm-thick steel plates + 2 external 15 mm-thick steel platesDynamic shear modulus: Gd = 1.1 MPaDamping : 5%

Shape factor S 11.25PGA 0.315 g (hard soil)Number of isolators 195Mass (t) ~110 000Isolation frequency (Hz) 0.6Service loading (NSd) 5.67 MN (σ = 7 MPa)Displacement dbd (mm) 108



1

courtesy of CEA


ITER

Experimental fusion tokamakF4E, Cadarache, France

ITER900x900x181 mm square bearing6 layers of 20 mm of elastomer5x 5 mm-thick steel plates + 2 external 15 mm-thick steel platesDynamic shear modulus: Gd = 1.1 MPaDamping : 5%

Shape factor S 11.25PGA 0.315 g (hard soil)Number of isolators 493Mass (t) ~ 300 000Isolation frequency (Hz) 0.55Service loading (NSd) 6.4 MN ( = 8 MPa)Displacement dbd (mm) 112



Lower bear ing plate

Connec tors

Non-shrinkage grout laye r La te ral removable stops

Elastome ric be aring

Upper bearing plate

1

courtesy of F4E/IO


Plant overview

Lower basemat

Plinth (or Pedestal)

Isolator

Shear studsUpperbearing plate

Lowerbearing plate

Lateral removablestops

Elastomeric bearing

2


Plant design

Similar design practice to non-isolated NPP design, except a few particularities,

Preliminary design : rigid body behaviour : 1 DOF system analysis ,or simplified rigid 3D model,

Detailed design stage (1/2) : 3D model of the structure,

Soil-Structure-Interaction,

Modal-spectral analysis is limited to projects usingbearings with linear behavior,

3D Time-history calculations contribution of the verticalmotion to the horizontal response

JHR (amplified deformation)

3


Plant design

Detailed design stage (2/2) Effects of construction sequence, creep and shrinkage (one model for each step), Specific temporary load cases (replacement of one or several bearings),

Bearing Input data: Real mechanical properties: standards formulae not 100% applicable for metric-size bearings full-scale tests Ranged mechanical isolators properties, including:

– Production tolerances → impact on production quality follow-up– Beginning / end of service life: ageing influence → accelerated ageing tests

qualification step

3


Plant design

Bearings layout optimization :Uniform vertical distribution of loads: ±20% of deviation (EC8)

reduction of torsional mode,

Constructibility & MaintenanceAccesses to plinths

Interfaces with reinforcement

Therefore, isolators plan layout to be adapted accordinglyPlinth Reinforcement interface

3


Plant design

Other design recommandations :Sizing the seismic gap, from Beyond Design evaluations and objectives,

Specific sizing of the pedestals (could be subjected to unusual loads for beyond-design earthquake),

Specific design of « beam-walls » connected to the upper raft,

3


Plant design

Qualification of the isolators“Real” mechanical properties Dynamic compression, dynamic shear:

effects of frequency / distortion variation on the stiffness and damping Creep test

Aged mechanical properties

Validation of scale effects on samples: full-scale bearings vssamples Used for accelerated ageing tests Used for monitoring after commissioning of the plant

Comparison of acceleratedageing tests on samples &

full-scale bearings

Creep test

Comparison of dynamicshear tests on samples & full-scale bearings

3


Safety requirements

Functional & Safety analysis of the Seismic Isolation (Safety Important Component)Stable (over time, radiations) & Resistant to fire

Robust & durable

Proper transmission of the loads

Repleacable

4


Safety requirements & design implications

Technological solution impacts the design criteriaFrench experience is based upon Elastomeric Bearings

Polychloroprene Rubber bearingCompounding: damping ratio tuned through Carbon black addition

No scragging: stiffness / damping stable over cyclic deformations

Predictible & stable creep

Gd from 0.4 to 1.4 MPa

Limited resistance to cold temperatures

Flame retardant: endothermic reactiondue to chlorid acid formation

Stability & Fire resistance

Robustness & durability

Load transmission

Repleacability

Cl

– CH2 – C = CH – CH2 –

Cl

– CH2 – C = CH – CH2 –

CR cross-linking system

4



Self-standing system: do not rely on any other mechanical system to damp the displacement

Damping ratio taken conservatively = 5 to 6% (LDRB - CR)

Lateral displacementUltimate distortion limited to 140% of elastomer thickness linear behaviour of the isolator on its working range

Possibly: hard-stop for beyond-design case (not implemented in France)

Long service life (up to 60 years)Creep under high distortion limited service compression: 7 to 8 MPa in service (up to 20 MPa in ultimate)

Radiation & Air exposure: oxidation stiffening accelerated ageing tests



Load transmission

Repleacability

Beyond design test – 400% shear strain

4



Accelerated ageingArrhenius law applicable for the stiffness (G): Ageing mechanisms are identical at Room Temperature and until 100°C Temperature accelerates ageing reactions

(Increase of Gd over service life) x (production tolerance) x (safety coefficient) = design value



Load transmission

Repleacability

T increases

0%

5%

10%

15%

20%

25%

30%

35%

40%

0 500 1000 1500 2000 2500 3000Time

P/

P 0

T1

T2

T3

T4

Gd/Gd0

X% increase in Gd

log(t)

log(t)

0

2

4

6

8

10

12

14

16

18

0.0025 0.0026 0.0027 0.0028 0.0029 0.0030 0.0031 0.0032 0.0033 0.0034 0.0035

1/T

ln(t)

Service temperature

Time in which Gd will have increasedby X% at service temperature

1/T

4



Horizontal loadFrom the isolator point of view: Friction between the isolator and the steel plates not taken into account in seismic event Shear studs & lateral removable stops

From the plinth point of view: sufficient margin against bending

Horizontal response not biased by the vertical stiffnessDesign criteria: limited initial rotation in the isolator at the end of installation → specific implementation at construction stage

up-to-date French seismic level: no tension in the isolators but allowed in EN15129

So far: min > 1 MPaFrom a technological point of view, easier replaceability



Load transmission

Repleacability

4



Ability to replacement to be taken into account

In the upper basemat design: layout & local bending

In the technology of the isolator

Sequence of works:1) load transfer (propping) design load case2) removal of lateral stops and “fuse” mortar layer3) replacement of the isolator4) recompression through a flat jack (injected with grout)



Load transmission

Repleacability

4


Equipments design

Design essentially similar to the design of equipments in a non-isolated nuclear structure: same design codes, same methodologies.Specificity arises from the type of loading, that must be carefully determined to capture cross-direction coupling effects. 3D building models are mandatory.

5


Equipments design

Specific design solutions developed for connections between the isolated and the non isolated structuresEx: Cruas NPP

5


THANK YOU

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