Interactions of actinides with cement corrosion products in chloride - PowerPoint PPT Presentation

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 2 nd International Workshop “Mechanisms and modelling of waste / cement interactions” October 12-16, 2008, Le Croisic 1 | 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 2 | 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 MgCl 2 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 dm 3 cement form blocks 3 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Long-term corrosion experiments • static experiments since 1979/1989 (INE: 1996) • simulated cemented waste samples doped with Cs nat and RN ( 237 Np, U nat , 137 Cs) • waste simulates correspond to products of spent nuclear fuel reprocessing ( Purex process; ~ 10 wt.% NaNO 3 ) • Ordinary Portland Cement • cement paste, water/cement ratio 0.3 – 0.5 • 160 dm 3 hardened cement blocks immersed in 400 dm 3 drums filled with leachant: MgCl 2 -brine (“Q-brine”), NaCl brine, tap water • experiments conducted at ambient conditions of LLW / ILW repository Asse salt mine (490-m level, 28° C) 4 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Long-term corrosion experiments • static experiments since 1979/1989 (INE: 1996) • simulated cemented waste samples doped with Cs nat and RN ( 237 Np, U nat , 137 Cs) • simulates correspond to products of spent nuclear fuel reprocessing ( Purex process; ~ 10 wt.% NaNO 3 ) • Ordinary Portland Cement • cement paste, water/cement ratio 0.3 – 0.5 • 160 dm 3 hardened cement blocks immersed in 400 dm 3 drums filled with leachant: MgCl 2 -brine (“Q-brine”), NaCl brine, tap water • experiments conducted at ambient conditions of LLW / ILW repository Asse salt mine (490-m level, 28° C) 5 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Initial composition of waste simulate (e.g. drum #33) sample #33 • cement phases comprise constituent mass / kg constituent mass / kg ~90% of sample Al (NO 3 ) 3 · 9 H 2 O 0.33 Portland cement 200 • nitrates minor components Ca (NO 3 ) 2 · 4 H 2 O 0.92 water 99.02 • accessories complexing Cr (NO 3 ) 3 · 9 H 2 O 0.06 total 336.00 agents (< 0.6 wt% in solid, Cu (NO 3 ) 2 · 3 H 2 O 0.06 inventory <3*10 -2 molal in Fe (NO 3 ) 3 · 9 H 2 O 0.29 water/cement 0.50 leachant: tartrate, citrate, Mg (NO 3 ) 2 · 6 H 2 O 0.82 oxalate Mn (NO 3 ) 2 · 2 H 2 O 0.03 waste content 11.0% • radionuclides doped in Ni (NO 3 ) 2 · 6 H 2 O 0.04 RN content trace concentrations Zn (NO 3 ) 2 · 6 H 2 O 0.07 U(nat) 5 MBq (few grams Np per sample Na-tartrat · 2 H 2 O 0.61 1 kg U nat per sample) Na-citrat · 2 H 2 O 0.59 Na 2 HPO4 · 12 H 2 O 1.31 significant complexation of U(VI), Np(V) Na 2 MoO 4 · 2 H 2 O 0.10 at aqueous concentrations of “free” 31.11 NaNO3 chelating agents > 10 -2 molal KNO 3 0.02 => scavenging of chelats by Ca 2+ , Mg 2+ …? 0.52 Na-oxalate NaF 0.10 6 | 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 7 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Laboratory experiments: Materials and methods (A) cement / brine equilibration experiments inactive corrosion of OPC paste (w/c = 0.4) in Q-, R- and conctr. MgCl 2 -brine at various mass cement / volume brine ratios (0.001 < m/V < 1.1 g cm -3 ) (B) Np, U sorption experiments adding aliquots of 237 Np(V), 233 U(VI) stock solutions to equilibrated cement / brine systems (variation in m cement / V brine ) (C) Np, U solubility experiments • dissolving Np, U solids in equilibrated solution of (A) cement / brine equilibration • dissolving Np, U solids in pure MgCl 2 - and NaCl-solutions (pH variation; NpO 2 , NpO 2 OH, UO 3 :2H 2 O, Na 2 UO 2 O(OH)) static experiments running for 6 – 24 months; Ar atmosphere (pO 2 , pCO 2 ≤ 1 ppm); powders of hardened cement paste (A) and cement corrosion product (B), respectively 8 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)

Laboratory experiments: solid material (A)cement / brine equilibration experiments - …) OPC paste, w/c = 0.4, without additives (NO 3 oxide content Ca(OH) 2 wt% CaO 66.87 SiO 2 17.29 Al 2 O 3 3.57 Ca-silicates 2000 TiO 2 0.25 1900 1800 Fe 2 O 3 3.27 1700 1600 MnO 0.07 1500 1400 MgO 1.56 1300 1200 K 2 O 1.63 Lin (Counts) 1100 clinker phases: 1000 Na 2 O 0.46 900 silicocarnotite, 800 SO 3 5.02 belite / larnite, d=3.18882 700 600 brownmillerite, 500 400 qypsum, 300 quartz, 200 100 calcite, 0 8 10 20 30 40 50 60 periclase (…) 2-Theta - Scale Asse_Zementklinker_2007_2te - File: Asse_Zementklinker_2007_2t 00-037-1496 (*) - Anhydrite, syn - CaSO4 - Orthorhombic 01-070-1488 (C) - Arcanite, syn - K2(SO4) - Orthorhombic Operations: Displacement 0.224 | Displacement 0.143 | Displaceme 00-005-0586 (*) - Calcite, syn - CaCO3 - Hexagonal (Rh) 00-026-1071 (I) - Calcium Silicate Sulfate - Ca5(SiO4)2SO4 - Orthor 01-086-0402 (C) - Hatrurite, syn - Ca3SiO5 - Monoclinic 00-046-1045 (*) - Quartz, syn - SiO2 - Hexagonal 00-033-0302 (*) - Larnite, syn - Ca2SiO4 - Monoclinic 00-009-0413 (*) - Mayenite, syn - Ca12Al14O33 - Cubic 00-030-0226 (*) - Brownmillerite, syn - Ca2(Al,Fe+3)2O5 - Orthorho 00-033-0311 (*) - Gypsum, syn - CaSO4·2H2O - Monoclinic 9 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT) clinker 00-038-1429 (*) - Calcium Aluminum Oxide - Ca3Al2O6 - Cubic 00-045-0946 (*) - Periclase, syn - MgO - Cubic 00-032-0148 (I) - Calcium Aluminum Oxide - Ca3Al2O6 - Monoclinic 01-074-1742 (C) - Aphthitalite - NaK3(SO4)2 - Hexagonal 00-032-0150 (*) - Calcium Aluminum Oxide - Ca3Al2O6 - Orthorho 01-076-0623 (C) - Rankinite - Ca3Si2O7 - Monoclinic

MgCl 2 rich leachants: initial compositions equilibrated brine in system R-brine Q-brine Mg 2+ mol (kg H 2 O) -1 NaCl-KCl-MgCl 2 -Na 2 SO 4 -H 2 O 5.2 4.2 Na + mol (kg H 2 O) -1 0.2 0.4 K + mol (kg H 2 O) -1 0.3 0.5 Mg Cl - mol (kg H 2 O) -1 10 9 R-brine 2- mol (kg H 2 O) -1 SO 4 0.4 0.2 KMgCl 3 :6H 2 O (Crn) val (kg H 2 O) -1 ionic strength 16.5 13.8 K + KMgClSO 4 :2.75 H 2 O Q-brine (Kai) experiments with Q-brine, R-brine, 4 molal MgCl 2 solution + NaCl KCl (Syl) (Hal) MgCl 2 brines slightly acidic due to Mg 2+ hydrolysis and aggressive vs. OPC 2K SO 4 10 | 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 mass cement to volume brine ratio of equilibrated systems 11 | 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 K sp , 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-H 2 O • Al, Si aqueous species, Pitzer parameters • solubility products, log K sp , 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 12 | Institut für Nukleare Entsorgung (INE) | Karlsruhe Institute of Technology (KIT)