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Interactions of actinides with cement corrosion products in chloride rich solutions: modelling and experimental results V. Metz, B. Kienzler, M. Altmaier, A. Bauer, E. Bohnert, M. Schlieker Institute for Nuclear Waste Disposal (INE) Research

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1 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Interactions of actinides with cement corrosion products in chloride rich solutions: modelling and experimental results

  • V. Metz, B. Kienzler, M. Altmaier, A. Bauer, E. Bohnert, M. Schlieker

Institute for Nuclear Waste Disposal (INE) Research Centre Karlsruhe / Karlsruhe Institute of Technology Germany

2nd International Workshop “Mechanisms and modelling of waste / cement interactions” October 12-16, 2008, Le Croisic

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2 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Acknowledgments

  • F. Geyer, S. Hilpp, M. Nesovic, M. Plaschke, J. Römer, E. Soballa and
  • C. Walschburger (INE) for carrying out DTA, ICP-MS, OES, SEM-

EDS, Raman and XRF analyses

  • R. Odoj and team for core drilling at FZJ-IEF6
  • K. Garbev (ITC-TAB) for assistance in evaluating XRD data

HMGU Asse and Bundesamt für Strahlenschutz, BfS, for technical support during probing of full-scale experiments and partial funding of the study

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3 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Background - Objectives corrosion of cemented radioactive waste forms (LLW / ILW) under conditions of a repository in rock salt

durability of cemented waste forms in brine? geochemical evolution of brine / secondary phases? radionuclide retention?

  • studying corrosion of cement forms in MgCl2 brine
  • studying interactions of Np, U with cement corrosion products
  • comparison of modelling predictions to results of
  • short-term laboratory experiments with (Np, U doped) cement powders and
  • long-term full-scale experiments with (Np, U doped) doped waste simulates /

~200 dm3 cement form blocks

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4 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

  • static experiments since 1979/1989 (INE: 1996)
  • simulated cemented waste samples

doped with Csnat and RN (237Np, Unat,137Cs)

  • waste simulates correspond to products of

spent nuclear fuel reprocessing (Purex process; ~ 10 wt.% NaNO3)

  • Ordinary Portland Cement
  • cement paste, water/cement ratio 0.3 – 0.5
  • 160 dm3 hardened cement blocks immersed

in 400 dm3 drums filled with leachant: MgCl2-brine (“Q-brine”), NaCl brine, tap water

  • experiments conducted at ambient conditions
  • f LLW / ILW repository Asse salt mine

(490-m level, 28° C)

Long-term corrosion experiments

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5 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

  • static experiments since 1979/1989 (INE: 1996)
  • simulated cemented waste samples

doped with Csnat and RN (237Np, Unat,137Cs)

  • simulates correspond to products of spent

nuclear fuel reprocessing (Purex process; ~ 10 wt.% NaNO3)

  • Ordinary Portland Cement
  • cement paste, water/cement ratio 0.3 – 0.5
  • 160 dm3 hardened cement blocks immersed

in 400 dm3 drums filled with leachant: MgCl2-brine (“Q-brine”), NaCl brine, tap water

  • experiments conducted at ambient conditions
  • f LLW / ILW repository Asse salt mine

(490-m level, 28° C)

Long-term corrosion experiments

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6 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Initial composition of waste simulate (e.g. drum #33)

sample #33 constituent mass / kg constituent mass / kg Al (NO3)3 · 9 H2O 0.33 Portland cement 200 Ca (NO3)2 · 4 H2O 0.92 water 99.02 Cr (NO3)3 · 9 H2O 0.06 total 336.00 Cu (NO3)2 · 3 H2O 0.06 Fe (NO3)3 · 9 H2O 0.29 water/cement 0.50 Mg (NO3)2 · 6 H2O 0.82 Mn (NO3)2 · 2 H2O 0.03 waste content 11.0% Ni (NO3)2 · 6 H2O 0.04 RN content Zn (NO3)2 · 6 H2O 0.07 U(nat) 5 MBq Na-tartrat · 2 H2O 0.61 Na-citrat · 2 H2O 0.59 Na2HPO4 · 12 H2O 1.31 Na2MoO4 · 2 H2O 0.10 NaNO3 31.11 KNO3 0.02 Na-oxalate 0.52 NaF 0.10

  • cement phases comprise

~90% of sample

  • nitrates minor components
  • accessories complexing

agents (< 0.6 wt% in solid, inventory <3*10-2 molal in leachant: tartrate, citrate,

  • xalate
  • radionuclides doped in

trace concentrations (few grams Np per sample 1 kg Unat per sample) significant complexation of U(VI), Np(V) at aqueous concentrations of “free” chelating agents > 10-2 molal => scavenging of chelats by Ca2+, Mg2+ …?

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7 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Core drilling in glove box

after approaching steady state (with respect to solution composition) termination & core drilling

  • dry drilling performed at

Research Centre Jülich

  • due to production of

contaminated dust drilling in glove box

  • samples from various

depth and lateral positions

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8 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

static experiments running for 6 – 24 months; Ar atmosphere (pO2, pCO2 ≤ 1 ppm); powders of hardened cement paste (A) and cement corrosion product (B), respectively (A) cement / brine equilibration experiments inactive corrosion of OPC paste (w/c = 0.4) in Q-, R- and conctr. MgCl2-brine at various masscement / volumebrine ratios (0.001 < m/V < 1.1 g cm-3) (B) Np, U sorption experiments adding aliquots of 237Np(V), 233U(VI) stock solutions to equilibrated cement / brine systems (variation in mcement / Vbrine) (C) Np, U solubility experiments

  • dissolving Np, U solids in equilibrated solution of (A) cement / brine equilibration
  • dissolving Np, U solids in pure MgCl2- and NaCl-solutions (pH variation; NpO2,

NpO2OH, UO3:2H2O, Na2UO2O(OH))

Laboratory experiments: Materials and methods

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9 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

00-026-1071 (I) - Calcium Silicate Sulfate - Ca5(SiO4)2SO4 - Orthor 01-070-1488 (C) - Arcanite, syn - K2(SO4) - Orthorhombic 01-076-0623 (C) - Rankinite - Ca3Si2O7 - Monoclinic 01-074-1742 (C) - Aphthitalite - NaK3(SO4)2 - Hexagonal 00-045-0946 (*) - Periclase, syn - MgO - Cubic 00-033-0311 (*) - Gypsum, syn - CaSO4·2H2O - Monoclinic 00-009-0413 (*) - Mayenite, syn - Ca12Al14O33 - Cubic 00-046-1045 (*) - Quartz, syn - SiO2 - Hexagonal 00-005-0586 (*) - Calcite, syn - CaCO3 - Hexagonal (Rh) 00-037-1496 (*) - Anhydrite, syn - CaSO4 - Orthorhombic 00-032-0150 (*) - Calcium Aluminum Oxide - Ca3Al2O6 - Orthorho 00-032-0148 (I) - Calcium Aluminum Oxide - Ca3Al2O6 - Monoclinic 00-038-1429 (*) - Calcium Aluminum Oxide - Ca3Al2O6 - Cubic 00-030-0226 (*) - Brownmillerite, syn - Ca2(Al,Fe+3)2O5 - Orthorho 00-033-0302 (*) - Larnite, syn - Ca2SiO4 - Monoclinic 01-086-0402 (C) - Hatrurite, syn - Ca3SiO5 - Monoclinic Operations: Displacement 0.224 | Displacement 0.143 | Displaceme Asse_Zementklinker_2007_2te - File: Asse_Zementklinker_2007_2t

Lin (Counts)

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000

2-Theta - Scale

8 10 20 30 40 50 60 d=3.18882

(A)cement / brine equilibration experiments OPC paste, w/c = 0.4, without additives (NO3

  • …)

Laboratory experiments: solid material

  • xide

content wt% CaO 66.87 SiO2 17.29 Al2O3 3.57 TiO2 0.25 Fe2O3 3.27 MnO 0.07 MgO 1.56 K2O 1.63 Na2O 0.46 SO3 5.02

Ca(OH)2 Ca-silicates clinker clinker phases: silicocarnotite, belite / larnite, brownmillerite, qypsum, quartz, calcite, periclase (…)

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10 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

K+

equilibrated brine in system NaCl-KCl-MgCl2-Na2SO4-H2O

Mg SO4 2K

KMgClSO4:2.75 H2O (Kai)

KMgCl3:6H2O (Crn)

KCl (Syl) + NaCl (Hal) Q-brine MgCl2 rich leachants: initial compositions R-brine

R-brine Q-brine Mg2+ mol (kg H2O)-1 5.2 4.2 Na+ mol (kg H2O)-1 0.2 0.4 K+ mol (kg H2O)-1 0.3 0.5 Cl- mol (kg H2O)-1 10 9 SO4

2-

mol (kg H2O)-1 0.4 0.2 ionic strength val (kg H2O)-1 16.5 13.8

experiments with Q-brine, R-brine, 4 molal MgCl2 solution MgCl2 brines slightly acidic due to Mg2+ hydrolysis and aggressive vs. OPC

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11 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Geochemical simulations: conceptual model

Reaction path modeling:

  • initial thermodynamic equilibrium between solution and solid phase computed
  • infinitesimal amount of reactant cement paste "added" to solution
  • new equilibrium calculated including precipitation of super-saturated solid phases
  • in next step, again infinitesimal amount of reactant added to altered solution (…)

reaction progress (time) increase in masscement to volumebrine ratio of equilibrated systems

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12 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Calculation methods

  • EQ3/6 software package (Geochemist’s Workbench)
  • concentrated salt solutions: Pitzer activity model
  • Harvie-Moller-Weare database Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O

including brucite, Mg-oxychloride, Ca-oxychlorides, calcite, Mg-hydroxocarbonates …

  • simplifications necessary due to lack of thermodynamic data (e.g. Pitzer parameters)
  • EQ3/6 data0.hmw database extended for solubility products, log Ksp, complexation

constants, log β, and ion-interaction coefficients (Pitzer parameters):

  • Np(V), U(VI) solids, aqueous species, Pitzer param. for Mg-Na-H-Cl-OH-H2O
  • Al, Si aqueous species, Pitzer parameters
  • solubility products, log Ksp, of alumosilicate / aluminate endmembers:

hydrotalcite 4MgO.Al2O3.10H2O, quartz SiO2, chlorite endmembers, e.g. clinochlore Mg5Al2Si3O10(OH)8, smectite endmembers e.g. Ca-saponite Ca.165Mg3Al.33Si3.67O10(OH)2

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13 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Modeling predictions

1 2 3 4 5 6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 mass(cement) - volume(brine) ratio / g cm-3

  • concentr. / mol (kg H2O)-1

7 8 9 10 11 12 13

  • log(m H+)

p

  • log(mH+)

Mg Ca Na SO4

2-

  • Mg Ca exchange

in solid phases

  • Mg(aq) decrease
  • Ca(aq) increase
  • pH increase
  • Na constant
  • SO4

2-, Al, Si

relatively low conctr.

saponite / CaSO4 chlorite / Mg-oxy

  • hydrotalc. / Mg-oxy
  • hydrotalc. / brucite
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14 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

50 100 150 200

  • 3
  • 2
  • 1

1 5 6 7 concentration / log (mol dm-3)

SO

4 2-

Ca K Na Mg

tim e / days

pH

pHexp

Results of laboratory experiments corrosion of OPC powder in MgCl2 brine

specific experimental series for 0.001 < m/V < 1.1 g cm-3 Solution composition within few weeks approaching apparent steady-state ΔC/Δt -> 0 when ΔC ≤ analytical uncertainty In concentrated MgCl2 solution high detection limit Si, Al conctr. < detection limit

e.g. masscement / volumebrine 0.1 g cm-3

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15 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Al Ca Mg Na Fe K

10

  • 4

10

  • 3

10

  • 2

10

  • 1

Reaktionszeit 0 , 3, 150 Tage

Menge im Feststoff [g Element (g Feststoff)

  • 1]

Results of laboratory experiments corrosion of OPC powder in MgCl2 brine

XRF: Composition of solid material

  • depletion of Ca content
  • strong increase in Mg
  • no significant change in Fe (Si)

minor components

  • increase in Na, decrease in K, no

significant change in Al

Reaction time 0 d, 3 d, 150 d amount in solid / g element (g sample)-1

SEM-EDS: secondary phases

  • Mg-oxychloride (except m/V > 0.75 g cm-3)
  • Mg-silicates and Mg-Ca-silicates
  • halite

e.g. masscement / volumebrine 0.1 g cm-3

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16 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

10 20 30 40 50 60 70 80 90

CSH-Phase CSH-Phase Quarz Calcit Calcit

Brucit Brucit Brucit

Calcit Calcit Calcit Calcit Calcit Portlandit Portlandit CSH-Phase, Calcit

Brucit Brucit

Portlandit Portlandit

  • norm. intensity

2°θ (Cu Kα) raw cement (OPC type PZ35) solids after 3 days solids after 150 days

Results of laboratory experiments corrosion of OPC powder in MgCl2 brine

Summary of XRD results

  • steady state after few weeks –

no significant difference in mineralogical composition to samples after 150 days

  • secondary phases:

Mg-oxychloride (except m/V > 0.75), hydrotalcite, gypsum, (brucite, quartz)

  • hydration relics: hydrogarnet
  • clinker relics: silicocarnotite, belite /

larnite, brownmillerite e.g. masscement / volumebrine 0.1 g cm-3

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17 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

1 2 3 4 5 6 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 mass(cement) - volume(brine) ratio / g cm-3 concentration / mol (kg H2O)-1 7 8 9 10 11 12 13

  • log(m H+)

Comparison simulations with lab results

  • log(mH+)

Mg Ca Na SO4

2-

saponite / CaSO4 chlorite / Mg-oxy

  • hydrotalc. / Mg-oxy
  • hydrotalc. / brucite

Experimental data: Steady state results of specific experim. series OPC in R-brine 0.001 < m/V <1.1 g cm-3

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18 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Comparison results of simulation with results of laboratory / full-scale experiments

10

  • 2

10

  • 1

10 10

  • 6

10

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 10

1

6 7 8 9 10 11 12 1000 2000 3000 4000

pH Ca S Mg concentration / mol (kg H2O)

  • 1

reaction progress Zi / kg cement (kg H2O)

  • 1

pHEQ3/6 time / d

Laboratory experiments: Steady state results OPC in R-brine / Q-brine (stars) Full-scale experiments: temporal evolution of waste simulate in Q-brine (small symbols) Simulation: evolution of OPC in Q-brine (lines)

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19 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

10

  • 2

10

  • 1

10 10

  • 6

10

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 10

1

6 7 8 9 10 11 12 1000 2000 3000 4000

pH Ca S Mg concentration / mol (kg H2O)

  • 1

reaction progress Zi / kg cement (kg H2O)

  • 1

pHEQ3/6 time / d

With respect to solution composition waste components don’t affect significantly overall solution evolution up-scaling of lab results (volume scale; powder / cement block) Fair agreement between results of simulation with results of laboratory / full-scale experiments Full-scale experiment(s) close to equilibrium?

Comparison results of simulation with results of laboratory / full-scale experiments

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20 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Full-scale experiments: XRD and SEM-EDS characterization of final solid samples

Homogenous lateral and vertical distribution of mineral phases (except calcite enrichment in first 10 cm) Hydrotalcite, ettringite, gypsum, halite, brucite +/- Mg-oxychloride calcite (mainly surface zone)

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21 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Full-scale experiments: nitrate and DTA-TG analyses of final solid samples

  • homogenous distribution of mineral phases in corroded cement blocks
  • formation of stable secondary phases with respect to solution composition

(hydrotalcite, gypsum, halite, brucite +/- Mg-oxychloride) indicate equilibration of cement / brine systems of full-scale experiments within ~25 years

Summary of nitrate analyses no significant radical / vertical variation in nitrate content (additionally steady state in aqueous nitrate concentration) Summary of DTA-TG analyses

  • homogenous distribution of phases containing

OH-, SO3-, CO2-groups (homogenous DTA-TG patterns)

  • exception calcite enrichment in outer surface zone

calcite content in internal zones < 2 wt%

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22 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Variation of U concentration with time: full-scale experiments

10

  • 2

10

  • 1

10 10

  • 6

10

  • 5

10

  • 4

10

  • 3

10

  • 2

10

  • 1

10 10

1

6 7 8 9 10 11 12 1000 2000 3000 4000 pH Ca S Mg concentration / mol (kg H2O)

  • 1

reaction progress Zi / kg cement (kg H

2O)

  • 1

pHEQ3/6 time / d

changes in solution composition affects changes in U conctr.

1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 5 10 15 20 time / years concentration / mol (kg H2O)-1

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23 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Laboratory experiments on U(VI) solubility

  • 8
  • 7
  • 6
  • 5
  • 4
  • 3
  • 2
  • 1

3 4 5 6 7 8 9 10 11 12

log [U(VI)]

  • log [H+]

0.25 m MgCl2 (+ 0.5 m NaCl) 5.15 m MgCl2 2.67 m MgCl2 MgCl2 saturated with brucite or Mg oxychloride

UO3:2H2O transformation into NaUO2O(OH)

Altmaier, M. et al., Solubility of U(VI) in NaCl and MgCl2 solutions (in prep.)

  • 9
  • 8
  • 7
  • 6
  • 5
  • 4
  • 3
  • 2
  • 1

3 4 5 6 7 8 9 10 11 12 13 14

(14) (13) (35) Solution in equilibrium with both solids (XRD) log Ko

sp = - 29.8

UO3

.2H2O(s)

log Ko

sp = - 22.65

Na2U2O7xH2O(s)

log [U(VI)]

  • log [H+]

NaCl brine

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24 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Comparing U concentrations in full-scale experiments to solubility of U(VI) phases

UO3:2H2O NaUO2O(OH) U(VI) concentration controlled by solubility of schoepite – or – NaUO2O(OH)

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25 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Np(V) solubility experiments

In full-scale experiments, 1*10-10 M Np measured after 9 years, increased to 8±4·10-10 M after ~15 years – Np concentration far below NpO2OH solubility

  • 6
  • 5
  • 4
  • 3
  • 2
  • 1

7 8 9 10 11 12

log [Np(V)]

  • log [H+]

MgCl2 satd. with Mg oxychloride MgCl2 satd. with brucite 0.25 m MgCl2 5.15 m MgCl2 2.67 m MgCl2

Neck, Altmaier, Müller, Metz, Kienzler (2003): FZK-INE 001/01

sorption phenomena controlling Np in full-scale experiments?

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26 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Np(V) sorption experiments: kinetics

50 100 150 200 250 300 10

  • 7

10

  • 6

10

  • 5

initial V/m = 9 cm

3 g

  • 1

initial V/m = 100 cm

3 g

  • 1

initial V/m = 20 cm

3 g

  • 1

blank solution

Np / mol (kg H2O)

  • 1

time / days

  • adding aliquots of 237Np(V) stock solutions to equilibrated cement / Q-brine systems
  • main mineral phases: Mg-oxychloride, hydrotalcite, gypsum
  • sufficient inventory of equilibr. phases: same solution composition for changing V/m
  • measured Np(V) concentrations, <10-6 M, far below NpO2OH solubility

sorption equilibrium approached after 50 days

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27 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Np(V) sorption experiments

  • 7.5
  • 7.0
  • 6.5
  • 6.0
  • 5.5
  • 7.5
  • 7.0
  • 6.5
  • 6.0
  • 5.5

concentration linear fit q = 1.14C - 0.8 R

2 = 0.996

loading, log q / log(mol g

  • 1)

concentration, log C / log(mol L

  • 1)

results of equilibrated sorption experiments linear isotherm derived from log (Np loading mol/g) vs. log (Npaq mol/L) based on sorption coefficient, Np concentration in the full scale experiment is calculated to be 1.3±0.3·10-9 M - compared to 8±4·10-10 M measured after ~15 yrs.

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28 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Conclusions

Homogenous distribution of mineral phases in corroded cement blocks – and - formation of stable phases (hydrotalcite, gypsum, halite, brucite +/- Mg-oxychloride) indicate equilibration of cement / brine full-scale experiments within ~25 years Simulated evolution of MgCl2-brine / cement system as a function of corrosion progress is found to be in fair agreement with results of full scale experiments and laboratory experiments Due to high U inventory of the full scale experiments, U concentrations in solution aliquots correspond to calculated solubilities of schoepite / NaUO2O(OH)(s) Observations suggest that Np retention is controlled by adsorption onto cement corrosion products rather than by solubility phenomena Waste components (nitrate, oxalate …) do not affect significantly geochemical evolution / behaviour of Np, U

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29 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Outlook

TRePro II 2009 Workshop on Modelling of Coupled Transport Reaction Processes Karlsruhe, Germany, March 18 - 19, 2009 Contact: Johannes Lützenkirchen <johannes@ine.fzk.de> Open Post-Doc Position Interactions of radionuclides with cement corrosion products Contact: Volker Metz <volker.metz@kit.edu>

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30 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Thanks for your attention!

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31 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Txt

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32 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Experimental systems

sample doping water/cement leachant start of termination ratio leaching (drilling) #25 U(nat) 0.3 Q-brine 1984 #26 U(nat) 0.34 Q-brine 1984 #28 Cs-137 0.43 Q-brine 1984 2006 #33 U(nat) 0.5 Q-brine 1989 2006 #34 U(nat) 0.5 Q-brine 1989 #35 Np-237 0.5 NaCl-brine 1989 #36 Np-237 0.5 Q-brine 1989

320 – 340 kg cement forms with 237Np 11 Bq/g, Unat ~15 Bq/g, 137Cs 550 Bq/g

  • periodical solution sampling - monitoring aqueous phase
  • analyzing surface precipitates
  • after approaching steady state (with respect to solution

composition) termination & core drilling - solid sampling

  • 137Cs doped sample: evolution cement / brine system
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33 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

pHexp = pHPitzer - ΔpH = -log mH+ - A

Pitzer (EQ3/6) convention: ψCl-/Cl-/H+ = ψ/Cl-/H+/H+= θCl-/Cl-= θH+/H+=0

log(γH+)Pitzer = log(γCl-)Pitzer = 2log(γ±)HCl

Grambow & Müller: Q-brine, saturated NaCl brine Altmaier, Neck & Müller: NaCl, MgCl2, CaCl2 0.1 – 5.5 m and mixed (Na2,Mg,Ca)Cl2 brines

Comparison pHexp with pHPitzer / -log mH+

  • log mH+ = pHexp + A

0.16 0.37 0.68 0.90 0.03 0.66 1.25 1.93 2.71 0.00 0.56 1.41 2.41 NaCl MgCl2 CaCl2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 1 2 3 4 5 6 7 8 9 10 11 msalt(mol kg

  • 1)

A

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34 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Application of Results

  • 800 m
  • 400 m

sea level +200 m

SW Low- and intermediate-level radwaste forms (LLW / ILW) emplaced in Zechstein diapirs, e.g. Asse salt mine (Germany):

  • ≈1300 drums ILW
  • ≈125000 drums LLW
  • ≈1015 Bq total RN inventory

(mainly Pu, U, Th, Cm, Np and Cs)

  • intrusion of MgCl2-rich Q-brine
  • >30000 t Portland cement (OPC)
  • ≈ 65000 m3 void volume

interaction of actinides with cement corrosion products critical for the long-term safety

  • f emplaced radwaste