I K **** Central Research Institute of Electric Power Industry a - PowerPoint PPT Presentation

1 Comparative Study Using Some Advanced Simulation Methods for Leaching of Cementitious Materials Over Ten Thousands of Years T. Torichigai*, K. Yokozeki*, T. Ishida**, K. Nakarai***, D. Sugiyama**** * KAJIMA corporation (JAPAN) ** The university of Tokyo *** Gunma university I K **** Central Research Institute of Electric Power Industry a R T

2 Background(1/3) Nuclear power generation covers 30 percents of power generation in Japan. Method for disposing radioactive waste is very important. RADIOACTIVE WASTE ○ High-level radioactive waste → Geological disposal (~-300m) ○ Low-level radioactive waste ・ Concrete Pit （ -10 ～ -5m ） I K a R ・ Sub-surface Disposal Underground T (-100 ～ -50m) (-100 ～ -50m)

Background(2/3) 3 Cross sectional view of sub-surface disposal repository Backfill （ Concrete or Soil) Tunnel Low diffusion layer (Mortar) Waste packages Low permeability layer (Bentonite) Reinforced concrete pit Concrete pit ： Maintaining stability of the repository I K a Mortar ： Preventing radioactive nuclides to leak R T Bentonite ： Preventing underground water to permeate to the repository

Background(3/3) 4 Long-term durability (over 10,000 years) is demanded for this repository Evaluating long-term durability of concrete is necessary Mortar Ca 2+ Issues for cementitious material *Crack Ca 2+ Ca 2+ *Chemical degradation Ca 2+ *Calcium leaching to underground water Bentonite *Chemical reaction between I K a Concrete R mortar and bentonite T

Target of this study 5 Simulation-code for evaluating calcium leaching for example… DuCOM, LIFE D.N.A., CCT-P ※ Method of simulation is different. Evaluating calcium leaching of cement hydrates by 3 codes. •What kind of deterioration will occur in sub-surface disposal repository? I K a • How fast is the deterioration speed? R T

Evaluating method for calcium leaching 6 Numerical Simulations Dissolution/Precipitation of Hydrates � Thermodynamic database � Solid-liquid equilibrium for calcium & Mass Transfer � Advection � Diffusion � Electrical potential Experimental Models I K L=a x t 1/n n ; parameter (generally n=2) a R a ; constant parameter T

Comparison of 3 codes 7 Chemical reactions Model of Code diffusion coefficient Cementitious material Bentonite ・ δ φ * Solid/liquid equilibrium for calcium Absorption of S ・ ・ = D D DuCOM eff Ω ion Ca ions * Solid/liquid equilibrium for calcium Absorption of LIFE (considering with Na, K) Ca ions ( ) = η ⋅ β ⋅ φ ⋅ i i D f D * precipitation of CaCO 3 ,Mg(OH) 2 ， D.N.A. eff 0 Friedel’s salt. * Thermodynamic database Ion exchange * Incongruent dissolution of C-S-H reactions of n ⎛ ⎞ φ ( t ) CCT-P ・ ⎜ ⎟ = D ( t ) D ( 0 ) ⎜ ⎟ * Dissolution/ precipitation of Na, K, Ca and Mg φ ⎝ ⎠ ( 0 ) CaCO 3 I K a R T

Simulation model 8 migration of Calcium ion 3.0m 1.0m 1.0m 6.0m Concrete Bento- Rock Mortar nite 2E-9 6.6E-13 2.8E-10 3.3E-13 Boundary line (constant) Diffusion coefficient(m 2 /s) Composition of underground water (mmol/l) Ca 2+ Na + K + Mg 2+ 2- Cl - 2- SO 4 CO 3 pH I K a R 0.13 0.77 0.03 0.16 0.14 0.44 0.62 8.6 T

Conditions 9 Mix proportions of concrete and mortar Unit Quantity (kg/m 3 ) W/B Air （ % ） ( ％ ) W LPC FA LSP S G Concrete 45 2.5 160 249 107 249 832 786 Mortar 45 2.5 230 358 153 307 1223 - Cement hydrates using in calculation DuCOM ; Portlandite, C-S-H LIFE D.N.A. ; Portrandite, C-S-H, Calcite, Brucite, Friedel’s salt, NaOH, KOH I K a CCT-P ; All hydrates in database R T

Simulation result of calcium leaching rate at 50,000 years 10 Rock Concrete Bentonite 100 ％） DuCOM 80 Calcium leaching rate（ LIFE D.N.A. CCT- P 60 40 20 0 decrease of Leaching depth - 20 Precipitations diffusion coefficient - 40 2.5 3.0 3.5 4.0 4.5 Distance from boundary line（ m） Faced to Bentonite I K Leaching depth ： DuCOM ＞ LIFE D.N.A. ＞ CCT-P a R T Faced to Rock Leaching depth ： DuCOM ＞ CCT-P ＞ LIFE D.N.A.

Evaluating for calcium leaching speed 11 Calcium leaching speed of concrete (faced to rock) 600 DuCOM 500 LIFE D.N.A. leaching depth(mm) CCT- P 400 300 200 100 0 0 50 100 150 200 250 I K a time（ √ year） R T Leaching speed ： DuCOM ＞ LIFE D.N.A. ＞ CCT-P

Evaluating for calcium leaching speed 12 Calcium leaching speed of concrete (faced to rock & bentonite) 600 600 DuCOM 500 500 LIFE D.N.A. leaching depth(mm) leaching depth(mm) CCT- P 400 400 DuCOM Na+，K+ from Bentonite LIFE D.N.A. 300 300 control Calcium leaching CCT- P from concrete 200 200 100 100 0 0 0 50 100 150 200 250 0 50 100 150 200 250 I K a time（ time（ √ year） √ year） R T

Degradation process of cement hydrates 13 CH leaching CSH leaching Concrete Concrete Bento Rock DuCOM nite D increase D increase Precipitate (Calcite, Brucite, Friedel’s salt ) Bento LIFE Rock nite D.N.A. D increase D increase D decrease Precipitate(Calcite) Na + , K + Bento CCT-P I K Rock a nite R T D increase D increase D;diffusion coefficient

Changing in diffusion coefficient 14 Dissolution/precipitation of cement hydrates ... Porosity increase/decrease ... Diffusion coefficient increase/decrease 2 / s) 1E- 10 ・ δ φ S DuCOM ・ ・ = Diffusion coefficient(m D D eff Ω ion LIFE D.N.A. CCT- P 1E- 11 ( ) = η ⋅ β ⋅ φ ⋅ i i D f D eff 0 1E- 12 n ⎛ ⎞ φ ( t ) ・ ⎜ ⎟ = D ( t ) D ( 0 ) ⎜ ⎟ φ ⎝ ⎠ ( 0 ) 1E- 13 I K a 0 25 50 75 100 R Calcium leaching rate(% ) T

Influential factor for Calcium leaching 15 • Changing in diffusion coefficient • Chemical reaction (especially, precipitation) • Degradation process of cement hydrate is different I K a R • Calcium leaching speed is different T

Conclusions 16 Evaluating calcium leaching of cement hydrates by 3 codes. •What kind of deterioration will occur in sub-surface disposal repository? � Portlandite & C-S-H leach from cementitious material � Secondary minerals would precipitate � Degradation process is different in 3 codes • How fast is the deterioration speed? � Calcium leaching speed is DuCOM > LIFE D.N.A.>CCT-P � Calcium leaching depth at 50,000 years are 130~500mm � The reason why simulation result is different… Changing in diffusion coefficient I K a Chemical reaction (especially, precipitation) R T

17 Appendix I K a R T

DuCOM 18 Dissolution/Precipitation of Hydrates Calcium liquid/Solid equilibrium Mass Transfer � Transport by solution flow � Transport by diffusion ・ δ φ S ・ ・ = D D eff Ω ion I K a R T Calcium leaching = Porosity increase = D increase

LIFE D.N.A. 19 Dissolution/Precipitation of Hydrates Calcium liquid/Solid equilibrium Mass Transfer C P0Ca � Transport by solution flow ① Ca 2+ Concentration in Solid C p1Ca =A Cp1 ･C P0Ca Ca(OH) 2 � Transport by diffusion ② � Electric force C P2Ca C- S- H ( ) ③ = η ⋅ β ⋅ φ ⋅ i i 1 / n ⎛ ⎞ C D f D C ⎜ ⎟ = ･ pCa Ca A ⎜ ⎟ eff 0 cp 1 ⎝ ⎠ C C p 0 Ca 0 Ca C 0Ca C 1Ca Ca 2+ Concentration in liquid ions ( ) ・ φ = + φ φ φ 2 f 0.001 0.07 {1.8( - 0.18) H( - 0.18) I K − ⋅ a 1 c G R β = 1 ⋅ vol P T − ⋅ vol d S Transition vol zone

CCT-P 20 Dissolution/Precipitation of Hydrates � the thermodynamic database Mass Transfer (Chemical reaction code HARPHRQ) � Transport by solution flow � Incongruent dissolution of C-S-H � Transport by diffusion − − − i 1 i 1 i 1 x x x = − + log K log K log( ) i + 0 i + + n 1 x 1 x 1 x ⎛ ⎞ φ ( ) t ・ ⎜ ⎟ = − − D ( t ) D ( 0 ) ⎧ ⎫ ⎜ ⎟ x 1 1 x x φ + + 2 ⎝ ⎠ ( 0 ) ⎨ ⎬ A A A ( ) 0 i 1 i + 2 i + + ⎩ ⎭ 2 1 x 1 x ( 1 x ) logK sp of C-S-H gel depend on the rate of Ca/Si I K a R T

Investigation result of the old structures 21 60 Lagerblad(2001) Yokozeki(2002) 50 Saito et al.(2003) Ca leaching depth (mm) ： Y=2.42√ t Leaching depth at 50,000years=541mm 40 ： Y=0.94√ t Leaching depth at 50,000years=210mm 30 The most deteriorated data 20 Average of all data 10 0 0 20 40 60 80 100 120 Time (years) I K a R Simulation results = 130 ～ 500mm at 50,000 years T

Comparison DuCOM to LIFE D.N.A. 22 1.0 C P0Ca rate of Ca concentration in 0.8 ① ① Ca 2+ Concentration in Solid Ca(OH) 2 DuCOM solid/ initial ② ② 0.6 LIFE DNA C- S- H (model change) 0.4 OPC ③ Model(OPC) 0.2 LPCFA Model(LPCFA) 0.0 C 1Ca C 0Ca C 0Ca 0 5 10 15 20 25 Ca 2+ Concentration in liquid Ca concentration in liquid（ mmol/ l） <Different type of cement> <affect Na ions & K ions> 250 1,000year 200 Leaching depth(mm) 200 10,000year 150 97.5 100 I K 42.5 a 50 R T 0 LIFE D.N.A. LIFE D.N.A. DuCOM (Model change)