scholarly journals Thermochemical characterization of Ca4La6(SiO4)6(OH)2 a synthetic La- and OH-analogous of britholite: implication for monazite and LREE apatites stability

Mineralogia ◽  
2008 ◽  
Vol 39 (1-2) ◽  
pp. 41-52 ◽  
Author(s):  
Emilie Janots ◽  
Fabrice Brunet ◽  
Bruno Goffé ◽  
Christophe Poinssot ◽  
Michael Burchard ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Temperature Drop ◽  
Formation Enthalpy ◽  
Solution Calorimetry ◽  
Chemical Durability ◽  
Chemical System ◽  
Constant Composition ◽  
Nuclear Waste Forms ◽  
Low Solubility

Thermochemical characterization of Ca4La6(SiO4)6(OH)2 a synthetic La- and OH-analogous of britholite: implication for monazite and LREE apatites stabilityIn this contribution, monazite (LREEPO4) solubility is addressed in a chemical system involving REE-bearing hydroxylapatite, (Ca, LREE)10(PO4,SiO4)6(OH)2. For this purpose, a synthetic (La)- and (OH)-analogous of britholite, Ca4La6(SiO4)6(OH)2, was synthesised and its thermodynamic properties were measured. Formation enthalpy of -14,618.4±31.0 kJ·mol-1 was obtained by high-temperature drop-solution calorimetry using a Tian-calvet twin calorimeter (Bochum, Germany) at 975 K using lead borate as solvent. Heat capacities (Cp) were measured in the 143-323 K and 341-623 K ranges with an automated Perkin-Elmer DSC 7. For calculations of solubility diagrams at 298 K, the GEMS program was used because it takes into account solid solutions. In conditions representative of those expected in nuclear waste disposal, calculations show that La-monazite is stable from pH = 4 to 9 with a minimum of solubility at pH = 7. La-bearing hydroxylapatite precipitates at pH > 7 with a nearly constant composition of 99% hydroxylapatite and 1% La-britholite. Each mineral buffers solution at extremely low lanthanum concentrations (log{La} = 10-10-10-15 mol·kg-1 for pH = 4 to 13). In terms of chemical durability, both La-monazite and La-rich apatite present low solubility, a requisite property for nuclear-waste forms.

HIPed Tailored Pyrochlore-Rich Glass-Ceramic Waste Forms for the Immobilization of Nuclear Waste

2008 ◽  
Vol 1124 ◽  
Author(s):  
Melody Lyn Carter ◽  
Hui Li ◽  
Yingjie Zhang ◽  
Andrew L Gillen ◽  
Eric R Vance
Keyword(s):  
Nuclear Waste ◽  
Glass Ceramic ◽  
Glass Ceramics ◽  
Spectroscopic Characterization ◽  
Chemical Durability ◽  
Intermediate Level ◽  
Crystalline Phases ◽  
Waste Forms ◽  
Ceramic Samples

AbstractHot isostatically pressed (HIPed) glass-ceramics for the immobilization of uranium-rich intermediate-level wastes and Hanford K-basin sludges were designed. These were based on pyrochlore-structured Ca(1-x)U(1+y)Ti2O7 in glass, together with minor crystalline phases. Detailed microstructural, diffraction and spectroscopic characterization of selected glass-ceramic samples has been performed, and chemical durability is adequate, as measured by both MCC-1 and PCT-B leach tests.

The Application of 57FE Mössbauer Spectroscopy to the Characterization of Nuclear Waste Forms

1981 ◽  
Vol 6 ◽  
Author(s):  
Paul G. Huray ◽  
M. T. Spaar ◽  
S. E. Nave ◽  
J. M. Legan ◽  
L. A. Boatner ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Chemical Properties ◽  
Electronic Charge ◽  
Chemical Information ◽  
Waste Forms ◽  
Charge States ◽  
Physical And Chemical ◽  
Nuclear Waste Forms

The electronic charge states and site symmetries of the radioactive ions incorporated in nuclear waste forms are of considerable importance in determining the physical and chemical properties of these materials. An in situ characterization of these ions is, unfortunately, often difficult – especially when a mixture of charge states and local crystal symmetries exist. The application of Mbssbauer spectroscopy represents a powerful technique for obtaining solid state chemical information.

Comparison of Glass and Crystalline Nuclear Waste Forms

1988 ◽  
Vol 127 ◽  
Author(s):  
W. Lutze ◽  
R. C. Ewing
Keyword(s):  
Mechanical Properties ◽  
Performance Assessment ◽  
Nuclear Waste ◽  
Single Phase ◽  
Chemical Durability ◽  
Borosilicate Glasses ◽  
Thermal And Mechanical Properties ◽  
Materials Properties ◽  
Waste Forms ◽  
Nuclear Waste Forms

ABSTRACTNuclear waste forms may be divided into two broad categories: (1) single phase glasses with minor crystalline components (e.g., borosilicate glasses) and (2) crystalline waste forms, either single phase (e.g., monazite) or polyphase (e.g., SYNROC). This paper reviews the materials properties data that are available for each of these two types of waste forms. The prinicipal data include: (1) physical, thermal and mechanical properties, (2) chemical durability; (3) radiation damage effects. Complete data are only available for borosilicate glasses and SYNROC; therefore, this comparison focuses on the performance assessment of borosilicate glass and SYNROC.

Phase evolution and chemical durability of co-doped Gd2Zr2O7 ceramics for nuclear waste forms

2015 ◽  
Vol 41 (5) ◽  
pp. 6344-6349 ◽  
Author(s):  
Xirui Lu ◽  
Long Fan ◽  
Xiaoyan Shu ◽  
Sijin Su ◽  
Yi Ding ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Phase Evolution ◽  
Chemical Durability ◽  
Waste Forms ◽  
Nuclear Waste Forms ◽  
Co Doped

Rapid synthesis and chemical durability of Gd2Zr2-Ce O7 via SPS for nuclear waste forms

2018 ◽  
Vol 44 (16) ◽  
pp. 20306-20310 ◽  
Author(s):  
Shunzhang Chen ◽  
Xudong Liu ◽  
Xiaoyan Shu ◽  
Jingxian Yang ◽  
Lan Wang ◽  
...  
Keyword(s):  
Nuclear Waste ◽  
Chemical Durability ◽  
Rapid Synthesis ◽  
Waste Forms ◽  
Nuclear Waste Forms

scholarly journals Ab Initio Investigation of Helium Mobility in La2Zr2O7 Pyrochlore

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 667
Author(s):  
Yanxia Lu ◽  
Qing Peng ◽  
Chenguang Liu
Keyword(s):  
Nuclear Waste ◽  
Density Functional ◽  
Minimum Energy ◽  
Elastic Band ◽  
Waste Forms ◽  
Band Method ◽  
And Migration ◽  
High Level ◽  
Migration Pathways ◽  
Nuclear Waste Forms

The α-decay of incorporated actinides continuously produces helium, resulting in helium accumulation and causing security concerns for nuclear waste forms. The helium mobility is a key issue affecting the accumulation and kinetics of helium. The energy barriers and migration pathways of helium in a potential high-level nuclear waste forms, La2Zr2O7 pyrochlore, have been investigated in this work using the climbing image nudged elastic band method with density functional theory. The minimum energy pathway for helium to migrate in La2Zr2O7 is identified as via La–La interstitial sites with a barrier of 0.46 eV. This work may offer a theoretical foundation for further prospective studies of nuclear waste forms.

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