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Crack modeling of the SUPERCONTAINER main body Overview and status on 6/6/6 Johan Bel ONDRAF/NIRAS Alain Van Cotthem

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Crack modeling of the SUPERCONTAINER main body Overview and status on 6/6/6 Johan Bel ONDRAF/NIRAS Alain Van Cotthem TRACTEBEL/SUEZ. Crack!!. PLAN. General context Supercontainer buffer : concrete choice - First step 2D modeling of the main body

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slide1

Crack modeling of the SUPERCONTAINER main body Overview and status on 6/6/6Johan BelONDRAF/NIRASAlain Van Cotthem TRACTEBEL/SUEZ

Crack!!

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide2
PLAN
  • General context
  • Supercontainer buffer : concrete choice - First step
  • 2D modeling of the main body
  • Concrete choice confirmation: the need for large scale tests
  • Conclusion

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

general context
General context
  • Starting point for the choice of a concrete buffer for the Supercontainer: ONDRAF/NIRAS with help of experts laid out basic requirements categorized in
        • Absolute must
        • Recommended
        • « nice to have »
  • The need exists to demonstrate feasibility for such a large concrete container in terms of:
        • Workability (lab tests)
        • Staging of the fabrication process(next study stages)
        • Control of cracking :
          • 2D/3D calculation
          • Intermediate large scale tests

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

general context4
General context
  • Basically an iterative process between:
    • Ondraf/Niras
    • Consultancy (Magnel, TBL)
    • Manufacturer (Socea, Ronveaux,…)
    • Corrosion and concrete experts panel
    • Supplier of basic components (Carmeuse, Degussa, …)
    • GTA and SFC coordination team

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide5

General program :

WP1:concrete lab testing (characterization) and feasibility study

  • Galson study

We are here

WP2 : test of fabrication methods (classic, spun concrete, self-compacting,..)

WP3: small scale testing 2nd and 3rd phase

Design and manufacturing specification

WP4: crack behavior modeling

WP5: supercontainer mock-up (scale 1/1)

WP6: supercontainer heater test

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

concrete choice a typical mass concrete problem

Step 4 : Third phase concrete and lid

Step 1 : prefab shell concrete phase 1

Step 2 : container insert

Step 3 : Second phase concrete

Concrete choice : a typical mass concrete problem
  • hydration residual stresses
  • workability (homogeneity, segregation,…)

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

concrete choice a phasing problem on going study
Concrete choice : a phasing problem (on going study)

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide8

Concrete choice, First step :

Is the initial composition adequate ?

  • Labo tests on small samples were carried out by two independent companies (Socea and Ronveaux) with large industrial experience
  • Initially, the composition from the “Galson” report was used :

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide9

Concrete choice, First step :

Is the initial composition adequate ?

Workability of mortar without super plasticizer is poor

=> very dry concrete (compaction problems, risk for segregation,…)

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide10
Different possibilities to tackle this problem:
      • Higher Water/Cement ratio: up to 0.55 - 0.6
      • Use of superplasticizer (polycarboxylate based)
      • Self Compacting Concrete =SCC (filler + super plasticizer)
      • “Spun” concrete :

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide11

Crack modeling(Preliminary 2D approach)

Modeling has run in parallel with experimental adequacy lab tests

  • First 2D-modeling study carried out by Belgatom in collaboration with university of Ghent (prof De Schutter)
  • 2 D Modeling deemed necessary on order to:
    • verify overall crack risks depth due to hydration and waste heat in the middle section
    • Help set up experimental program for unknown or important parameters
    • advice on some design related aspects (use of steel bars, use of anchors, closing details, shape adjustment,…) => 3D modeling needed for this purpose

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide12

Crack modeling : basic assumptions

  • CEM I 32.5 C30/37 350 kg/m³
  • 2 Dmodel Simplifications (I) :
  • no iterative process has been used to take into account the reduced section in tension
  • no material strength properties reduction due to T (15 % max)
  • creeping effect is taken into account by using a reduced young’s modulus curve.
  • based exclusively on bibliographical data’s
  • it is only valid at the mid section (end effects are not taken into account)

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide13

Crack modeling : basic assumptions

  • 2 D model Simplifications (II) :
  • Systus® software was used based on integral solving but material history has to be considered => incremental solving (↔ non linearity) was replaced by :
  • Constants :
      • Thermal expansion coefficient
      • Thermal conductivity
      • Specific Heat capacity

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide14

Crack modeling : basic assumptions

2 D model Simplifications (III) :

  • the behaviour is closer to the adiabatic state then isothermal
  • Two curing conditions:
    • 5 W/m²°C applied on the inner wall and 16 W/m²°C on the outer wall (ventilated hall)
    • 5 W/m²°C on both boundaries (adiabatic hall)
  • The annular gap filling with cementitious grout or dry powder/pellets (lime or portlandite) (other E ) is not modelled

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide15

Crack modeling : basic assumptions

2 D model Simplifications (III) : adiabatic curves from literature /standards

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide16

Crack modeling : basic assumptions

  • basic formula’s (I)
  • Compressive strength, tensile strength, modulus based on EUROCODE and variable with equivalent time

Compressive strength

tensile strength

Young modulus

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide17

Crack modeling : basic assumptions

  • basic formula’s (II)
  • Hydration heat

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide18

Crack modeling : Model

Cross-section

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

what is exactly calculated
What is exactly calculated ?
  • Step 1 : Temperature distribution due to hydration heat (solve heat equation)
  • Step 2 : Corresponding displacement and stress distribution (longitudinal, radial, circumferential) in every point of the Supercontainer as a function of time from the beginning of the hardening (~8 hours) until equilibrium
  • Thermo-elastic calculation (T,M) => T,H,M not necessary ?
  • Only the first stage in the fabrication proces is modelled (2D) => further modelling will consider also other fabrication and handling stages and will be more detailed (3D)
  • Both heat sources (cement hydration + HLW) are simulated
  • Calculated tensile tresses are compared with tensile strength to evaluate risk for cracking
  • Crack widths are NOT calculated

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide20

Crack modeling : Results prefab(I)

  • Temperature distribution (from red to blue )
    • Max after 36 hours
    • Equilibrium after 16 days

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide21

Contact stress with steel enveloppe

Crack modeling : Results prefab(II)

  • Radial stress(+ : tensile; - compressive )

Ventilated room

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide22

Crack modeling : Results prefab(III)

  • Circumf and long stresses(+ : tensile; - compressive ) :
    • Stress inversion with time
    • Residual stress after cooling down due to
      • T gradient history
      • non linearities
      • creep

Ventilated room

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide23

Crack modeling : Results prefab (IV)

  • Tensile stresses remain below tensile strength during fabrication :

admissible

computed

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide24

Crack modeling : Results prefab + waste (V)

Only 5 to 10 cm of (non reinforced) the outside border

of the Supercontainer may present micro-cracking :

Figure shows final stress state at equilibrium (extrados)

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide25

Crack modeling : Results (VI)

  • Stresses due to hydration are dependant of the curing and drying conditions
  • “Steam” curing may be envisaged and will lead to compressive residual main stresses at equilibrium and potentially better contact between envelope and concrete
  • Stresses in stainless steel envelope are very low
  • No separation between stainless steel envelope and concrete buffer is expected in the central section but verification on end plugs is necessary
  • “Adiabatic” curing conditions provide better contact between concrete and steel

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide26

Concrete choice confirmation tests

  • Unusual concrete (angulous aggregate, CEM I,..) hence no reliable bibliographical data’s
  • Missing information at young age on creep and hydration
  • Confirmation of strength parameters with time
  • Confirmation of Gas basic calculation values : gas entry pressure
  • Real scale observation of homogeneity, segregation and workability
  • Acquire reliable values for a complete 3 D model that will also predict the behaviour at the end piece (lid) and at the annular gap interface.

WHY (I) ?

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide27

Concrete choice confirmation tests

  • No more simplifications : incremental, tensile zone, creep, shrinkage, use of hydration rate α(t), based on adapted parameters values from tests

WHY (II) ?

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide28

Concrete choice confirmation tests

HOW ?

On representative 6 m high samples with different concrete composition

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide29

Concrete choice confirmation tests

HOW ?

A

A’

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide30

Concrete choice confirmation tests

HOW ?

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide31

Concrete choice : Latest decisions

  • Isothermal test shows CEM I 42.5 could be used
    • availibility in Belgium
    • Guarantee of supply on the long term
  • SCC concrete composition is considered as the most promising one but « normal » concrete with superplasticizer will also be considered ( vibration !!)
  • Spun concrete on hold (but only solution without superplasticizer)
  • Tests set-up under discussion with Magnel/Cstc/TBL
  • Interim report for 2d-modeling (Feb 2006) will be updated before testing

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

slide32

Conclusions

  • We are close to concrete choice, narrow down to few proposals
  • Choice will be strongly justified through a step by step approach
  • Cracking will likely be controlled
  • Pending :
    • end plug (lid) and annular gap filling
    • necessity and behaviour of the steel enveloppe (3 D modeling needed)
    • Behavior under dynamic loading (normal and accidental) => modeling+tests

Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

requirements for the supercontainer buffer material
Requirements for the supercontainer buffer material

CATEGORY 1 : ABSOLUTE MUSTS (no compromise is to be accepted )

BUF_R1.1 use of pure PORTLAND cement CEM I

BUF_R1.2 Cement HSR:  to better resist to sulphur species present in Boom Clay pore water

BUF_R1.3 Aggregates only based on calcareous (CaCO3) materials:  sand and filler (if applicable) included ! No siliceous materials allowed

BUF_R1.4 No other organic additives but the superplasticizer

slide34

CATEGORY 2 : RECOMMENDED (a certain margin or flexibility of the requirement can be accepted )

BUF_R2.1 Cement with limited  hydration heat production to avoid or limit cracking : preferably CEM I 32.5 but if availabity is a problem 42.5 LH (low heat) & N (normal hardening) can be acceptable (hydration heat test Q=f(t)  to be performed to compare 42.5 with 32.5 )

BUF_R2.2 Tensile strength 2 MPa (caracteristic value)  This value of 2 MPa may be reviewed if another cement (e.g. 42.5) is chosen

BUF_R2.3 Materials should be available in sufficient quantitities during long periods of time (use on an industrial scale only planned within several decennia)

BUF_R2.4 Superplasticizer preferably based on polycarboxylate (unifunctional)

BUF_R2.5 Good workability  - preferably pompable so S4 or even S5 during at least 60 to 90 minutes

slide35

CATEGORY 2 : RECOMMENDED (a certain margin or flexibility of the requirement can be accepted )

BUF_R2.6 Compressive strength sufficient to resist to mechanical normal and accidental (fall,..;)  loads  : no exact values can be given but a C30/37 or better concrete is a good starting point

BUF_R2.7 Micro-cracks are allowed (and cannot be avoided) but radial, through-going cracks that might jeopardize the radiological shielding capacity should be avoided

BUF_R2.8 Good quality, homogeneous and dense concrete (no quantitative values imposed)

slide36

CATEGORY 3 : NICE TO HAVE (if not fulfilled, this requirement will not jeopardize the concept )

BUF_R3.1 Water/cement factor : 0.4 à 0.45 no exact value imposed : can be derived from other requirements

BUF_R3.2 Compressive strength after 1 day, 7 days,... : no precise requirements ; fabrication  (e.g. time to keep casting form around concrete)  will be adapted to results

BUF_R3.3 cement content min 300 kg/m3

BUF_R3.4 avoid use of rebars or steel fibres

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