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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

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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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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  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. Concrete choice : a phasing problem (on going study) Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. Crack modeling : basic assumptions • basic formula’s (II) • Hydration heat Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

  18. Crack modeling : Model Cross-section Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

  19. 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

  20. 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

  21. 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

  22. 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

  23. 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

  24. 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

  25. 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

  26. 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

  27. 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

  28. 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

  29. Concrete choice confirmation tests HOW ? A A’ Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

  30. Concrete choice confirmation tests HOW ? Exchange meeting EIG Euridice-SCK/CEN-ONDRAF/NIRAS - June 6, 2006

  31. 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

  32. 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

  33. 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

  34. 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

  35. 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)

  36. 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 back

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