• Deslandes, Alec
• Shi, Jingyu
• Gerber, Christoph
• Kelka, Uli
• Esteban, Lionel
• Crane, Punjehl
• Bourdet, Julien
• Suckow, Axel
• Camilleri, Michael
• Sari, Mustafa
• Sander, Regina
• Shen, Baotang
• Raiber, Matthias
• Wilske, Cornelia
• Sheldon, Heather
• Frery, Ema
• Josh, Matthew
• Sarout, Joel

Abstract

Australia is evaluating deep borehole disposal as a potential solution for its long-lived intermediate level waste (ILW). The project will aim to demonstrate by means of a comprehensive RD&D program the technical feasibility and the long-term safety of deep borehole disposal of appropriately conditioned long-lived ILW. The RD&D activities include demonstration of surface handling and full-scale field testing of waste/seal emplacement capabilities in a demonstration borehole whose dimensions are nominally put at 0.7 m (or 27.5 inch) bottom hole diameter and 2000 m deep. Pre- and post-closure safety assessments and safety case development are an integral part of the project. The paper introduces the framework that has been developed to streamline the RD&D activities and highlights several example activities. The focus in this paper is on geoscientific investigations that will underpin the long-term safety of deep borehole disposalThe framework for streamlining the RD&D activities is defined based on Safety and Feasibility Statements specific for deep borehole disposal [1]. Additional RD&D activities are grouped under Confidence Enhancement activities: these will further support the safety case with both qualitative and quantitative evidence as per the NEA safety case framework [2] and its adaptations for deep borehole disposal [3]. A system of traffic lights is used to illustrate the progress in each of these activities. Safety Statements are developed that aim to underpin the confidence in the long-term safety of deep borehole disposal. To this end generic geoscientific investigations have commenced, such as the development of novel enabling tools and methods that assist with site screening, including (i) geological fault network analysis and improved representation of seismic fault conceptualisations in numerical models, and (ii) experimental studies involving noble gas composition of deep rock fluid inclusions to interpret provenance and residence time of fluids. Further geoscientific studies have commenced to provide realistic rock properties for evaluation and input to assessment models; petrophysical, mineralogical, and geomechanical properties for crystalline rock and rock salt are being investigated. Radionuclide sorption behaviour to smectite clay has been studied using molecular dynamics simulation [4]. To provide bounding conditions about the thermal evolution of the disposal environment, heat transport calculations explored the sensitivity of temperature evolution within the borehole and rock environment to parameters such as heat load, borehole depth, geothermal gradients, and rock thermal conductivity. Preliminary post-closure safety assessments tested the need to consider coupled heat-flow processes for heat loads ranging from low (50 Watt/canister) to high (high-level waste). Feasibility Statements are considered that will support the claim that a deep disposal borehole can be constructed, waste can be emplaced and the borehole can be sealed in a manner that meets operational and long-term safety requirements. We report the findings from (i) container corrosion studies involving the application of coatings using cold-spray technology, (ii) numerical evaluation of borehole mechanical stability for several rock types under a range of stress conditions, and (iii) experimental studies on hydrogen transport in clay material deemed suitable for borehole sealing.References [1] Mallants D. et al. 2022. A framework for streamlining RD&D activities for deep borehole disposal. In: Waste Management 2022 Symposium; 6-10 March 2022; Phoenix, Arizona, USA.[2] NEA 2013. The Nature and Purpose of the Post-closure Safety Cases for Geological Repositories. NEA/RWM/R(2013)1, OECD/NEA, Paris, France. [3] Freeze, G. E. Stein, P.V. Brady, C. Lopez, D. Sassani, K. Travis, F. Gibb 2019. Deep Borehole Disposal Safety Case. SAND2019-1915, SANDIA NL, Albuquerque, NM, USA. [4] Zhang J., D. Mallants, P.V. Brady 2022. Molecular Dynamics Study of Uranyl Adsorption from Aqueous Solution to Smectite. Appl. Clay Sci. (https://doi.org/10.1016/j.clay.2021.106361).

Topics

• impedance spectroscopy
• surface
• corrosion
• inclusion
• simulation
• molecular dynamics
• Hydrogen
• thermal conductivity