Climate Considerations in Long-Term Safety Assessments for Nuclear Waste Repositories

ABSTRACTCement is used as a coating matrix for nuclear waste or as an engineered barrier of waste repositories situated in geological formations.The effect of mineral acids excreted by bacteria (Thiobacillus) or organic acids produced by fungi, on the biodegradation of cement is discussed. Organic acids are quantitatively and qualitatively determined during growth of fungi over a two-year period. Even with high pH conditions, pH of the cement ≈ 11, growth of microorganisms occurs.Biodeterioration of cement is expressed in terms of bioleaching velocity of calcium and is observed by electron microscopy.

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A natural cement analogue study to understand the long-term behaviour of cements in nuclear waste repositories: Maqarin (Jordan)

Applied Geochemistry ◽

10.1016/j.apgeochem.2016.05.009 ◽

2016 ◽

Vol 71 ◽

pp. 20-34 ◽

Cited By ~ 8

Author(s):

Lukas H.J. Martin ◽

Andreas Leemann ◽

Antoni E. Milodowski ◽

Urs K. Mäder ◽

Beat Münch ◽

...

Keyword(s):

Nuclear Waste ◽

Analogue Study ◽

Waste Repositories

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Thermodynamic Modeling of Neptunium(V) Solubility in Concentrated Na-CO3-HCO3-Cl-ClO4-H-OH-H2O Systems

MRS Proceedings ◽

10.1557/proc-353-1119 ◽

1994 ◽

Vol 353 ◽

Cited By ~ 1

Author(s):

Craig F. Novak ◽

Kevin E. Roberts

Keyword(s):

Nuclear Waste ◽

Chemical Properties ◽

Ion Extraction ◽

Concentrated Electrolytes ◽

Carbonate Complexation ◽

Report Data ◽

Safety Assessments ◽

Waste Repositories ◽

Groundwater Composition ◽

Coefficient Formalism

AbstractSafety assessments of nuclear waste repositories often require estimation of actinide solubilities as they vary with groundwater composition. Although a considerable amount of research has been done on the solubility and speciation of actinides,1,2 relatively little has been done to unify these data into a model applicable to concentrated brines. Numerous authors report data on the aqueous chemical properties of Np(V) in NaClO4, Na2CO3, and NaCl media, but a consistent thermodynamic model for predicting these properties is not available. To meet this need, a model was developed to describe the solubility of Np(V) in Na-Cl-ClO4-CO3 aqueous systems, based on the Pitzer activity coefficient formalism for concentrated electrolytes. Hydrolysis and/or carbonate complexation are the dominant aqueous reactions with the neptunyl ion in these systems. Literature data for neptunyl ion extraction and solubility are used to parameterize an integrated model for Np(V) solubility in the Np(V)-Na-CO3-HCO3-Cl-ClO4-H-OH-H2O system. The resulting model is tested against additional solubility and extraction data, and compared with Np(V) solubility experiments in complex synthetic brines.

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Bentonite clay barriers in nuclear waste repositories

E3S Web of Conferences ◽

10.1051/e3sconf/202020501003 ◽

2020 ◽

Vol 205 ◽

pp. 01003

Author(s):

Lyesse Laloui ◽

Alessio Ferrari ◽

Jose A. Bosch

Keyword(s):

Nuclear Waste ◽

Constitutive Models ◽

Bentonite Clay ◽

In Situ Experiment ◽

Future Prediction ◽

Bentonite Clays ◽

High Level ◽

Waste Repositories ◽

Clay Barriers

Deep disposal of high-level radioactive waste is the preferred solution worldwide for the long-term disposal of nuclear waste. This concept involves a series of geological and engineered barriers that provide isolation of the waste from the biosphere. Most designs involve bentonite clays as seals in different forms. During the operation of the repository, the bentonite will be subjected to a series of complex thermo-hydro-mechanical phenomena that will interact with each other. Predicting the long-term safety of geological repositories thus involve a rigorous analysis of these multi-physical processes. This paper presents a review of recent numerical approaches and analyses that have aimed to improve the understanding of processes that will take place in clay barriers over the lifetime of nuclear waste repositories. The understanding of bentonite behavior from laboratory experiments under relevant conditions is analyzed. Constitutive models that attempt to predict such behavior are presented, focusing on the stress-strain model ACMEG-TS. These models are implemented in the finite element code Lagamine which allows for the study of real scale tests. Two application cases are presented: the performance of a clay barrier according to the Swiss design, and a model of the FEEBX in situ experiment, which was modelled after a real repository under natural conditions. Overall, the relevant processes are well captured quantitatively by the models, allowing for the establishment of sound basis for future prediction and long-term design of the final underground repositories.

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Predicting Pu Concentrations in Solutions Contacting Geologic Materials

MRS Proceedings ◽

10.1557/proc-6-215 ◽

1981 ◽

Vol 6 ◽

Author(s):

Richard G. Strickert ◽

Dhanpat Rai

Keyword(s):

Nuclear Waste ◽

Safety Assessment ◽

High Level Waste ◽

Stable Phase ◽

Borosilicate Glasses ◽

Geologic Materials ◽

Solid Phases ◽

High Level ◽

Waste Repositories

ABSTRACTKnowledge of Pu solid phases present in nuclear wastes is important for predicting the geochemical behavior of Pu. Thermodynamic data and experimental measurements using discrete Pu compounds, Pu-doped borosilicate glasses (simulating a high-level waste form), and Pu contaminated sediments suggest that PuO2(c) is very stable and is expected to be present in the repository. The solubility of the stable phase, such as PuO2(c), can be used to predict the maximum Pu concentration in solutions for long-term safety assessment of nuclear waste repositories.

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