Perspectives on Performance Assessment and High-Level Waste Glass in a Geologic Repository

1993 ◽  
Vol 333 ◽  
Author(s):  
B.P. Mcgrail ◽  
D.W. Engel
Keyword(s):  
Performance Assessment ◽  
Reactive Transport ◽  
Waste Glass ◽  
High Level Waste ◽  
Secondary Phases ◽  
Geologic Repository ◽  
Large Computer ◽  
Computer Codes ◽  
Engineered Systems ◽  
High Level

ABSTRACTThe design and analysis of waste package and engineered systems for geologic disposal of radioactive wastes are being conducted in most countries with so-called performance assessment models and associated computer codes that solve the governing equations. The models range in complexity from simple 1-D analytical solutions to multidimensional, multicomponent reactive transport models implemented in large computer codes. Borosilicate waste glass is certainly the most studied and probably best understood waste form that has been developed for encapsulating high-level waste. Reasonably good models are available that describe the reaction kinetics and transformation of the glass into a paragenetic sequence of more stable secondary phases. Given the broad range of computational tools and extensive database on glass/water reactions that is available, it is surprising that little progress has been made to link these models and data in a comprehensive performance assessment of waste glass in a repository setting. In this paper, we will explore reasons why this linkage has not been developed, give several examples illustrating the importance of doing so, and illustrate an approach to accomplish such a linkage.

Analysis of reacted nuclear-waste glass using electron beams

1994 ◽  
Vol 52 ◽  
pp. 656-657
Author(s):  
E. C. Buck ◽  
N. L. Dietz ◽  
J. K. Bates
Keyword(s):  
Electron Microscopy ◽  
Analytical Electron Microscopy ◽  
Waste Glass ◽  
High Level Waste ◽  
Secondary Phases ◽  
Surface Areas ◽  
Transmission Electron ◽  
High Level ◽  
Long Term Behavior

When waste glass reacts with water, secondary phases may form, which will effect the distribution of radionuclides formally contained within the glass. In order to determine the long term behavior of waste glass, the secondary phases formed need to be identified. Analytical electron microscopy (AEM) is being used to characterize the secondary phases. Glasses have been reacted in test vessels at different surface areas to leachate volumes (S/V) and for periods in excess of 700 days. Increasing the S/V permits one to accelerate the reaction. Samples of the reacted waste forms are embedded in epoxy and thin sectioned by ultramicrotomy for observation in the transmission electron microscopy (TEM). Examinations were performed in a JEOL 2000FXII TEM operated at 200 kV. This abstract describes two types of glass tests, a high level waste sludge based glass and a low level waste glassy slag. Many hundreds of glass tests have been performed and examined by TEM to determine layer thickness, morphology of the leach layer, and identification of secondary phases.

A Coupled Chemical-Mass Transport Submodel for Predicting Radionuclide Release from an Engineered Barrier System Containing High-Level Waste Glass

1989 ◽  
Vol 176 ◽  
Author(s):  
B. P. McGrail ◽  
M. J. Apted ◽  
D. W. Engel ◽  
A. M. Liebetrau
Keyword(s):  
Mass Transport ◽  
Transport Model ◽  
Mechanistic Model ◽  
Waste Glass ◽  
High Level Waste ◽  
Precipitation Reaction ◽  
Geologic Repository ◽  
Silicate Mineral ◽  
High Level ◽  
Radionuclide Release

ABSTRACTA mechanistic model describing a dynamic mass balance between the production and consumption of silicic acid was coupled to a near-field mass transport model to predict the dissolution kinetics of a high-level waste glass in a deep geologic repository. The effects of interactions between an iron overpack and the glass are described by a time-dependent precipitation reaction for a ferrous silicate mineral. The kinetic model is used to transform radionuclide concentration-versus-reaction progress values, predicted from a geochemical reaction path computer code, to concentration-versus-time values that are used to calculate the rate of radionuclide release by diffusive mass transfer to the surrounding host rock. The model provides for both solubility-limited and kinetically limited release; the rate-controlling mechanism is dependent on the predicted glass/groundwater chemistry.

scholarly journals High-Level Waste Glass Compendium; What it Tells us Concerning the Durability of Borosilicate Waste Glass

1993 ◽  
Vol 333 ◽  
Author(s):  
J. C. Cunnane ◽  
J. M. Allison
Keyword(s):  
Performance Standards ◽  
The United States ◽  
Scientific Basis ◽  
Waste Glass ◽  
High Level Waste ◽  
Geologic Repository ◽  
Glass Corrosion ◽  
Corrosion Kinetics ◽  
High Level ◽  
Radionuclide Release

ABSTRACTFacilities for vitrification of high-level nuclear waste in the United States are scheduled for startup in the next few years. It is, therefore, appropriate to examine the current scientific basis for understanding the corrosion of high-level waste borosilicate glass for the range of service conditions to which the glass products from these facilities may be exposed. To this end, a document has been prepared which compiles worldwide information on borosilicate waste glass corrosion. Based on the content of this document, the acceptability of canistered waste glass for geological disposal is addressed.Waste glass corrosion in a geologic repository may be due to groundwater and/or water vapor contact. The important processes that determine the glass corrosion kinetics under these conditions are discussed. Testing data together with understanding of the long-term corrosion kinetics are used to estimate radionuclide release rates. These rates are discussed in terms of regulatory performance standards.

Performance assessment of the disposal of vitrified high-level waste in a clay layer

2001 ◽  
Vol 298 (1-2) ◽  
pp. 125-135 ◽  
Author(s):  
Dirk Mallants ◽  
Jan Marivoet ◽  
Xavier Sillen
Keyword(s):  
Performance Assessment ◽  
High Level Waste ◽  
Clay Layer ◽  
High Level

Performance Assessment of a High-Level-Waste Repository in Clay

1988 ◽  
Vol 127 ◽  
Author(s):  
Jan L. Marivoet ◽  
Geert Volckaert ◽  
Arnold A. Bonne
Keyword(s):  
Performance Assessment ◽  
Maximum Dose ◽  
High Level Waste ◽  
Clay Layer ◽  
Geological Disposal ◽  
Dose Rates ◽  
Consequence Analysis ◽  
Calculated Dose ◽  
Order Of Magnitude ◽  
High Level

ABSTRACTPerformance assessment studies have been undertaken on the geological disposal of high-level waste in a clay layer in the framework of the CEC project PAGIS. The methodology applied consists of two consecutive steps : a scenario and a consequence analysis. The scenario analysis has indicated that scenarios of normal evolution, of human intrusion, of climatic change, of secondary glaciation effects and of faulting should be evaluated. For the consequence analysis as well deterministic “best estimate” as stochastic calculations, including uncertainty, risk and sensitivity analyses, have been elaborated.The calculations performed show that most radionuclides decay to negligible levels within the first fewjneters of the clay barrier. Just a few radionuclides, 99Tc, 135Cs and 237Np with its daughter nuclides 233U and 229Th can eventually reach the biosphere. The maximum dose rates arising from the geological disposal of HLW, as evaluated by the “best-estimate” approach are about 10−11 Sv/y for river pathways. If the sinking of a water well into the 150 m deep aquifer layer in the vicinity of the repository is considered together with a climatic change, the maximum calculated dose rate rises to a value of 3×10−7 Sv/y. The maximum dose rates evaluated by stochastic calculations are about one order of magnitude higher due to the considerable uncertainties in the model parameters. In the case of the Boom clay the estimated consequences of a fault scenario are of the same order of magnitude as the results obtained for the normal evolution scenario. The maximum risk is estimated from the results obtained through stochastic calculations to be about 5×10−8 per year. The sensitivity analysis has shown that the effective thickness of the clay layer, the retention factors of Tc, Cs and Np, and the Darcy velocity in the aquifer are parameters which strongly influence the calculated dose rates.

Neptunium Speciation in Humic Acid-rich Clay Water upon Interaction With Radioactive Waste Glass Samples

2002 ◽  
Vol 757 ◽  
Author(s):  
V. Pirlet ◽  
P. Van Iseghem
Keyword(s):  
Humic Substances ◽  
Humic Acids ◽  
Specific Interaction ◽  
Waste Glass ◽  
High Level Waste ◽  
Boom Clay ◽  
Dissolution Tests ◽  
Vis Spectroscopy ◽  
Doped Glasses ◽  
High Level

ABSTRACTOrganic complexes of actinides are known to occur upon interaction of high level waste glass and Boom Clay which is a potential host rock formation for disposal of high level waste in Belgium. The solubility and mobility of 237Np, one of the most critical radionuclides, can be affected by the high dissolved organic carbon content of the Boom Clay porewater through complexation with the humic substances. The influence of humic substances on the Np behaviour is considered through dissolution tests of Np-doped glasses in Boom Clay water and through fundamental study of the specific interaction between Np(IV) and the humic acids using spectroscopic techniques. High Np(IV) concentrations are found in the glass dissolution tests. These concentrations are higher than what we should expect from the solubility of Np(OH)4, the solubility limiting solid phase predicted under the reducing conditions and pH prevailing in Boom Clay. Studying the specific interaction of Np(IV) with humic acids in Boom Clay porewater, high soluble Np concentrations are also measured and two main tetravalent Np-humate species are observed by UV-Vis spectroscopy. The two species are interpreted in terms of mixed hydroxo-humate complexes, Np(OH)xHA with x = 3 or 4. These species are the most likely species that can form according to the pH working conditions. Using thermodynamic simplified approaches, high complexation constants, i.e. log β131 and log β141 respectively equal to 46 and 51.6, are calculated for these species under the Boom Clay conditions.Comparing the spectroscopic results of the dissolution tests with the study of the interaction of Np(IV) with humic substances, we can conclude that the complexation of Np(IV) with the humic acids may occur and increases the solubility of Np(OH)4 upon interaction of a Np-doped glass and the Boom Clay porewater.

Vapour Phase Hydration of Blended Oxide - Magnox Waste Glasses

2003 ◽  
Vol 807 ◽  
Author(s):  
Neil C. Hyatt ◽  
William E. Lee ◽  
Russell J. Hand ◽  
Paul K. Abraitis ◽  
Charlie R. Scales
Keyword(s):  
Glass Matrix ◽  
Alkaline Earth ◽  
Vapour Phase ◽  
Waste Glass ◽  
High Level Waste ◽  
Zirconium Silicate ◽  
Constant Rate ◽  
Surface Alteration ◽  
High Level ◽  
Short Incubation Time

ABSTRACTVapour phase hydration studies of a blended Oxide / Magnox simulant high level waste glass were undertaken at 200°C, over a period of 5 – 25 days. The alteration of this simulant waste glass is characterised by a short incubation time of less than 5 days, leading to the formation of an alteration layer several microns thick. Following the incubation period, the alteration proceeds at a constant rate of 0.15(1)μmd−1. The distribution of key glass matrix (Si, Na) and waste (Cs, Zr, Nd, Mo) elements was found to vary significantly across the alteration layer. Vapour phase hydration leads to formation of surface alteration products, identified as smectite, zirconium silicate and alkaline-earth molybdate phases.

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