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23 pages, 6243 KiB

Open AccessArticle

How Findings from a Multi-Annual International Modeling Initiative Are Implemented in a Nuclear Waste Management Organization

by Jan-Olof Selroos and Björn Gylling

Energies 2023, 16(2), 684; https://doi.org/10.3390/en16020684 - 6 Jan 2023

Cited by 2 | Viewed by 1892

Abstract

In the present paper, we discuss various aspects of the SKB Task Force on Modeling of Groundwater Flow and Transport of Solutes (TFGWFTS). The TFGWTS is a multi-lateral forum for modeling of groundwater flow and solute transport, focusing on issues of relevance for [...] Read more.

In the present paper, we discuss various aspects of the SKB Task Force on Modeling of Groundwater Flow and Transport of Solutes (TFGWFTS). The TFGWTS is a multi-lateral forum for modeling of groundwater flow and solute transport, focusing on issues of relevance for disposal of nuclear waste. We discuss the objectives and set-up of the different tasks performed during the last 30 years, and specifically how the results of the modeling have informed performance and safety assessment applications within SKB (Swedish Nuclear Fuel and Waste Management Company, Solna, Sweden). We conclude that the TFGWFTS has been instrumental in developing modeling methodologies and tools, and in training and fostering modelers. While the early tasks were related to the construction of the Äspö Hard Rock Laboratory in Sweden and developed general modeling competence, the later tasks have served performance and safety assessment purposes in a more substantial manner. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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18 pages, 6483 KiB

Open AccessArticle

Contaminant Transport from a Deep Geological Repository: Lumped Parameters Derived from a 3D Hydrogeological Model

by Jiří Landa and Milan Hokr

Energies 2022, 15(18), 6602; https://doi.org/10.3390/en15186602 - 9 Sep 2022

Cited by 1 | Viewed by 2174

Abstract

A model of contaminant transport from a repository to the biosphere is one of the major needs in the safety assessment of the geological disposal of spent nuclear fuel. This work deals with the development of a procedure that obtained characteristic data from [...] Read more.

A model of contaminant transport from a repository to the biosphere is one of the major needs in the safety assessment of the geological disposal of spent nuclear fuel. This work deals with the development of a procedure that obtained characteristic data from the transport path by postprocessing the results of the 3D flow and transport models, according to the repository concept for the Czech Republic. Postprocessing was used to map the entire transport pathway, which included the smallest tracer flows; therefore, it is called the “integral method”. The results are the characteristics of the storage system, such as: transport path length, flow time, total dilution, groundwater flow, longitudinal dispersivity, porosity, etc. These acquired characteristics can be used directly in safety analyses or to narrow the selection of candidate sites. Furthermore, these parameters were used to set up a model with lumped parameters (in this case, created in the GoldSim SW environment). Even only one “Pipe” component, after being properly set up, shows almost identical results to the entire 3D model. Based on the results of the 3D model, it is possible to set up a lumped parameter model that accurately simulates the transport path and can perform further calculations of a larger number of contaminants in repeated runs, e.g., with stochastic input data, which would be very laborious (or not possible at all) with the 3D model. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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21 pages, 3961 KiB

Open AccessArticle

Capability for Hydrogeochemical Modelling within Discrete Fracture Networks

by David Applegate and Pete Appleyard

Energies 2022, 15(17), 6199; https://doi.org/10.3390/en15176199 - 26 Aug 2022

Cited by 1 | Viewed by 1707

Abstract

A new method for simulating solute transport and geochemical interactions within fractured rock is presented. This will be an important capability for assessing the safety of radioactive waste disposal facilities that are located within fractured crystalline bedrock. Specifically, the discrete fracture network (DFN) [...] Read more.

A new method for simulating solute transport and geochemical interactions within fractured rock is presented. This will be an important capability for assessing the safety of radioactive waste disposal facilities that are located within fractured crystalline bedrock. Specifically, the discrete fracture network (DFN) module within the ConnectFlow groundwater flow and transport software has been updated to: (i) simulate the advection and diffusion of more than one solute species (with the flow and transport equations coupled by the evolving density and viscosity); (ii) model the diffusion of solutes into the rock matrix between fractures; and (iii) utilise the iPhreeqc library to model chemical reactions involving solutes, minerals on fracture/pore surfaces and rock minerals. The performance of ConnectFlow’s DFN module has also been significantly improved via parallelisation which allows more complex calculations to be attempted. These developments are significant because hydrogeochemistry within fractured rock is more accurately represented in an explicit DFN, rather than using more approximate equivalent continuous porous medium (ECPM) methods. Illustrative calculations have been completed for the disposal facility for spent nuclear fuel at Olkiluoto in Finland, and the former candidate site for spent fuel disposal, Laxemar, in Sweden. These calculations show that DFN simulations provide results that are qualitatively similar to results from ECPM calculations. However, because the ECPM is a less direct approach, notable differences exist when compared to the DFN approach. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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26 pages, 13095 KiB

Open AccessArticle

Site Selection for a Deep Geological Repository in Switzerland: The Role of Performance Assessment Modeling

by Alexandros Papafotiou, Chao Li, Dominik Zbinden, Mohamed Hayek, Michael J. Hannon and Paul Marschall

Energies 2022, 15(17), 6121; https://doi.org/10.3390/en15176121 - 23 Aug 2022

Cited by 4 | Viewed by 2052

Abstract

In the development of deep geological repositories (DGRs), performance assessment modeling is used to evaluate the integrity and performance of the engineered and geological barriers for thousands or millions of years of evolution of the disposal system. To evaluate the suitability of a [...] Read more.

In the development of deep geological repositories (DGRs), performance assessment modeling is used to evaluate the integrity and performance of the engineered and geological barriers for thousands or millions of years of evolution of the disposal system. To evaluate the suitability of a site for a DGR, geoscientific data from dedicated site investigation programs are integrated into site-specific assessments. This paper presents the development and implementation of a modeling workflow aimed at comparing three potential siting areas for a DGR in Switzerland from the viewpoint of long-term safety and technical feasibility. The workflow follows the guidelines of the national regulator addressing safety relevant criteria such as the barrier efficiency of the host rock and its mechanical and chemical integrity in response to repository-induced influences and the long-term stability of the repository site over geological scales. In the regulatory requirements, the role of parametric, conceptual, and scenario uncertainty has been identified as an issue of special importance in the site selection process. The assessment approach comprises a portfolio of numerical models for the simulation of solute, gas and heat transport in the repository nearfield. The modeling was performed with deterministic as well as probabilistic variants integrated in an indicator-based approach that allows the consistent comparison of the candidate sites using quantitative dimensionless performance indices. The model-based assessment of the sites allows a traceable, transparent, and verifiable implementation of the site selection process. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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26 pages, 8569 KiB

Open AccessArticle

Numerical Assessments of Flow and Advective Transport Uncertainty for Performance Measures of Radioactive Waste Geological Disposal in Fractured Rocks

by Yun-Chen Yu, Yu-Hsiang Shen, Tsai-Ping Lee, Chuen-Fa Ni and I-Hsien Lee

Energies 2022, 15(15), 5585; https://doi.org/10.3390/en15155585 - 1 Aug 2022

Cited by 2 | Viewed by 1977

Abstract

Groundwater flow and transport are crucial for performance and safety assessment in the radioactive waste geological disposal. This study presents the groundwater flow and advective transport simulations for assessing the performance of a reference repository placed in fractured rocks. The study involves the [...] Read more.

Groundwater flow and transport are crucial for performance and safety assessment in the radioactive waste geological disposal. This study presents the groundwater flow and advective transport simulations for assessing the performance of a reference repository placed in fractured rocks. The study involves the concept of radionuclides migrating into the mobile water in fractures surrounding the deposition hole and calculates two specific quantitative indicators in the field of radioactive waste geological disposal. The indicators equivalent flow rate (Q_eq) and flow-related transport resistance (F) are used to express the groundwater flow and transport resistance in the host rock. Based on the hydrogeological conceptual model, the study employs DarcyTools to model the groundwater flow and advective transport of a base case. This study then conducts sensitivity analyses by varying the hydraulic conductivity of the key hydrogeological unit and the excavation damage zone. The uncertainty analysis employs multiple discrete fracture network (DFN) realizations to quantify the influences of DFNs on the flow and advective transport. Results show that the hydraulic conductivity of host rock dominates the flow and advective transport in the model domain, and the highest Q_eq is 1.91 × 10⁻⁴ m³/year, and the lowest F is 7.77 × 10⁵ year/m. Results also indicate that simulations of the hydraulic conductivity variations of hydrogeological units are more critical than those obtained from the variations of DFN realizations (i.e., the uncertainty analysis). The solutions could be useful for site investigations to modify the hydrogeological conceptual model in the study. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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23 pages, 7640 KiB

Open AccessArticle

Thermo-Hydro-Mechanical Coupled Modeling of In-Situ Behavior of the Full-Scale Heating Test in the Callovo-Oxfordian Claystone

by Yilong Yuan, Tianfu Xu, Fabrizio Gherardi and Hongwu Lei

Energies 2022, 15(11), 4089; https://doi.org/10.3390/en15114089 - 2 Jun 2022

Cited by 2 | Viewed by 2109

Abstract

Within the context for deep geological disposal (DGD) of high-level radioactive waste (HLW), thermo-hydro-mechanical (THM) coupled numerical modeling has become significantly important for studying the safe disposal of HLW. In this work, a 3D mechanical module is incorporated into the thermal–hydraulic (TH) coupled [...] Read more.

Within the context for deep geological disposal (DGD) of high-level radioactive waste (HLW), thermo-hydro-mechanical (THM) coupled numerical modeling has become significantly important for studying the safe disposal of HLW. In this work, a 3D mechanical module is incorporated into the thermal–hydraulic (TH) coupled code TOUGH2, thus forming an integrated THM coupled simulator referred to as TOUGH2Biot. The Galerkin finite element method is used to discretize the space for rock mechanical calculation. The mechanical process is sequentially coupled with the fluid and heat flow processes, which further gives feedback to the flow through stress-dependent hydraulic properties (e.g., porosity and permeability). Based on the available geological data at the Meuse/Haute-Marne Underground Research Laboratory (MHM URL) in France, the improved simulator is used to analyze the coupled THM behaviors of the Callovo-Oxfordian claystone (COx) induced by thermal loading. The anisotropy of material parameters (e.g., permeability and thermal conductivity) caused by the bedding and of in-situ stresses are well considered in our model. The numerical simulation can reasonably reproduce the field observations, including changes in temperature and pore pressure at monitoring boreholes during the ALC1604 experiment. The modeling results indicate that the anisotropic effects are remarkable, and temperature, pore pressure, and effective stress along the bedding increase more rapidly than in the vertical direction. Insight into numerical results through the visual model is beneficial for helping us to interpret the field observations and to understand the complex THM problem in the COx claystone formation. The numerical method and the modeling results presented in this work can be effectively used in support of performance assessment studies of HLW disposal sites to build confidence in the safety of future applications of nuclear energy systems. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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24 pages, 3456 KiB

Open AccessArticle

Analytical and Numerical Estimation of Fracture Initiation and Propagation Regions around Large-Diameter, Deep Boreholes for Disposal of Long-Lived Intermediate-Level Waste

by Jingyu Shi, Baotang Shen, Manoj Khanal and Dirk Mallants

Energies 2022, 15(7), 2445; https://doi.org/10.3390/en15072445 - 26 Mar 2022

Cited by 5 | Viewed by 2151

Abstract

The safety of high-level radioactive waste disposal has been studied across the world considering mined geologic repositories. Here, we introduce large-diameter, deep borehole disposal as one of the potential solutions for small volumes of long-lived intermediate-level waste (ILW). The short- and long-term stability [...] Read more.

The safety of high-level radioactive waste disposal has been studied across the world considering mined geologic repositories. Here, we introduce large-diameter, deep borehole disposal as one of the potential solutions for small volumes of long-lived intermediate-level waste (ILW). The short- and long-term stability of deep disposal boreholes is critical for environmental safety and public health. In this paper, we first use a recently revisited extensional strain criterion for fracture initiation and apply analytical solutions of a two-dimensional stress model to predict the fracturing region around a 2 km deep and 0.7 m diameter disposal borehole. Analytical solutions of fracture initiation are compared with results from the numerical simulator FRACOD, while the latter model also predicts dynamic effects such as fracture propagation. Both analytical and numerical methods predicted similar fracture initiation characteristics around the minor horizontal compressive stress springline, consistent with literature data. Numerical results showed deeper fracturing zones than those predicted by analytical solutions, mainly because the analytical predictions provide static snapshots under specific given conditions, while the numerical model calculates additional dynamic effects of fracture propagation. Including stress dynamics is shown to further weaken the rock around the borehole. At the bottom plane of the borehole, three-dimensional numerical simulations showed the development of fracturing zones around the major horizontal compressive stress springline. Borehole stability analyses are essential to plan the safe operation of drilling operations while also giving insights as to what borehole depths are more prone to fracturing and hence potentially less suitable as a waste disposal zone. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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Review

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16 pages, 811 KiB

Open AccessReview

Pragmatic Validation of Numerical Models Used for the Assessment of Radioactive Waste Repositories: A Perspective

by Stefan Finsterle and Bill Lanyon

Energies 2022, 15(10), 3585; https://doi.org/10.3390/en15103585 - 13 May 2022

Cited by 5 | Viewed by 2072

Abstract

The safety case for a radioactive waste repository relies heavily on results obtained by numerical models that assess the long-term performance of the engineered and natural barrier systems. Given that important engineering and public policy decisions are based on these models, it is [...] Read more.

The safety case for a radioactive waste repository relies heavily on results obtained by numerical models that assess the long-term performance of the engineered and natural barrier systems. Given that important engineering and public policy decisions are based on these models, it is essential that we critically evaluate their abilities and limitations, and thus justify the level of confidence we have in the inferences drawn from the modeling. In this article, we discuss some of the issues surrounding the modeler’s attempts to test, corroborate, confirm, and verify numerical models—a process sometimes referred to as model validation. This wide-ranging topic is approached by first examining its deep roots in the philosophy of science and hypothesis testing. However, the application of these principles to radioactive waste isolation calls for a more pragmatic approach, which has the narrower goal of corroborating site-specific models and their usefulness for a specific purpose. We focus on the practical aspects of validating hydrogeological models that are used to understand the evolution of the repository system. We will make the case that the responsible use of numerical models requires a sufficient understanding of the quality and robustness of the simulation results, with direct implications for how these results need to be interpreted, and how they can (or cannot) be used in support of important policy decisions. Full article

(This article belongs to the Special Issue The Role of Numerical Modelling in the Development of a Geologic Repository for Radioactive Waste)

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