Abstract When we call oil and gas fossil fuels, we admit that they were formed in the geological past and are therefore subject to depletion. Oil provides 40% of traded energy, 90% of transport fuel, and is critical for agriculture. The oil industry has great knowledge and experience. It has searched the world with sophisticated technology, always looking for the biggest and best prospects. Extrapolation of the discovery trend of the past, therefore, offers the best means of forecasting future discovery and production. Since oil has to be found before it can be produced, it follows that production has to mirror discovery after a time-lag. World discovery on this basis peaked in 1964, meaning that the corresponding peak of production is now imminent. The consensus of published reports of the total endowment of ‘conventional oil’ is just under 2000 × 10 9 barrels. To this has to be added bitumen, heavy oils, deepwater oil, polar oil and natural gas liquids, bringing the total to about 2700 × 10 9 bbl. Experience to-date shows that the peak in any country comes at, or before, the midpoint of depletion, which respects both the physics of the reservoir and the fact that most of the oil in any country occurs in a few large fields. Accordingly, we can expect global peak to come around 2010, followed not long afterwards by the peak or plateau of gas. The world must now prepare for the transition to declining oil and gas supply. Market economics that inevitably encourage rapid depletion have done immense damage by persuading governments to ignore resource constraints. In the past, geologists had a mission to identify the resources of the world for the benefit of mankind, and indeed they have still more to do in identifying what remains to be found in ever smaller and more difficult fields. But a far more important new mission is to explain just how finite the resources are, so that governments may adopt policies to cut demand, for which there is great scope, and bring on renewable energies as fast as possible. Failure to recognize the consequences of depletion leads to international tensions with countries vying with each other for access to the remaining oil supply, half of which lies in just five Middle East countries.

Abstract The Prototype Repository (PR) tunnel is located at the Äspö Hard Rock Laboratory near Oskarshamn in the southeast of Sweden. In the PR tunnel, six full-sized deposition holes (8.37 m deep and 1.75 m in diameter) have been constructed. Each deposition hole is designed to mimic the Swedish reference system for the disposal of nuclear fuel, KBS-3V. The PR experiment is designed to provide a full-scale simulation of the emplacement of heat-generating waste. There are three phases to the experiment: (1) the open tunnel phase following construction, where both the tunnel and deposition holes are open to atmospheric conditions; (2) the emplacement of canisters (containing heaters), backfill and seal in the first section of the tunnel; and (3) the emplacement of canisters, backfill and seal in the second section of the tunnel. This work describes the numerical modelling, performed as part of the engineered barrier systems (EBS) Task Force, to understand the thermo-hydraulic (TH) evolution of the PR experiment and to provide a better understanding of the interaction between the fractured rock and bentonite surrounding the canister at the scale of a single deposition tunnel. A coupled integrated TH model for predicting the wetting and the temperature of bentonite emplaced in fractured rock was developed, accounting for the heterogeneity of the fractured rock. In this model, geometrical uncertainties of fracture locations are modelled by using several stochastic realizations of the fracture network. The modelling methodology utilized information available at early stages of site characterization and included site statistics for fracture occurrence and properties, as well as proposed installation properties of the bentonite. The adopted approach provides an evaluation of the predictive capability of models, it gives an insight of the uncertainties to data and demonstrates that a simplified equivalent homogeneous description of the fractured host rock is insufficient to represent the bentonite resaturation.

Abstract Nuclear waste disposal in geological formations relies on a multi-barrier concept that includes engineered components – which, in many cases, include a bentonite buffer surrounding waste packages – and the host rock. Contrasts in materials, together with gradients across the interface between the engineered and natural barriers, lead to complex interactions between these two subsystems. Numerical modelling, combined with monitoring and testing data, can be used to improve our overall understanding of rock–bentonite interactions and to predict the performance of this coupled system. Although established methods exist to examine the prediction uncertainties due to uncertainties in the input parameters, the impact of conceptual model decisions on the quantitative and qualitative modelling results is more difficult to assess. A Swedish Nuclear Fuel and Waste Management Company Task Force project facilitated such an assessment. In this project, 11 teams used different conceptualizations and modelling tools to analyse the Bentonite Rock Interaction Experiment (BRIE) conducted at the Äspö Hard Rock Laboratory in Sweden. The exercise showed that prior system understanding along with the features implemented in the available simulators affect the processes included in the conceptual model. For some of these features, sufficient characterization data are available to obtain defensible results and interpretations, whereas others are less supported. The exercise also helped to identify the conceptual uncertainties that led to different assessments of the relative importance of the engineered and natural barrier subsystems. The range of predicted bentonite wetting times encompassed by the ensemble results were considerably larger than the ranges derived from individual models. This is a consequence of conceptual uncertainties, demonstrating the relevance of using a multi-model approach involving alternative conceptualizations.

Abstract A geological disposal facility (GDF) is the widely accepted long-term solution for the management of higher-activity radioactive waste. It consists of an engineered facility constructed in a suitable host rock. The facility is designed to inhibit the release of radioactivity by using a system consisting of engineered and natural barriers. The engineered barriers include the wasteform, used to immobilize the waste, the waste disposal container and any buffer material used to protect the container. The natural barrier includes the rocks in which the facility is constructed. The careful design of this multi-barrier system enables the harmful effects of the radioactivity on humans and biota in the surface environment to be reduced to safe levels. Bentonite is an important buffer material used as a component of a multi-barrier disposal system. For example, compacted bentonite rings and blocks are used to protect the copper container, used for the disposal of spent fuel, in the KBS-3 disposal system. As the bentonite saturates, through contact with groundwater from the host rock, it swells and provides a low hydraulic conductivity barrier, enabling the container to be protected from deleterious processes, such as corrosion. The characteristic swelling behaviour of bentonite is due to the presence of significant quantities of sodium montmorillonite. Recently, there have been detailed in situ experiments designed to understand how bentonite performs under natural conditions. One such experiment is the Buffer–Rock Interaction Experiment (BRIE), performed at the Äspö Hard Rock Laboratory near Oskarshamn in the SE of Sweden. This experiment is designed to further understand the wetting of bentonite from the groundwater flow in a fractured granite host rock. In this paper, the observations from the BRIE are explained using an integrated model that is able to describe the saturation of bentonite emplaced in a heterogeneous fractured rock. It provides a framework to understand the key processes in both the rock and bentonite. The predictive capability of these models was investigated within the context of uncertainties in the data and the consequence for predictions of the wetting of emplaced bentonite. For example, to predict the wetting of emplaced bentonite requires an understanding of the distribution of fracture transmissivity intersecting the bentonite. A consequence of these findings is that the characterization of the fractured rock local to the bentonite is critical to understanding the subsequent wetting profiles. In particular, prediction of the time taken to achieve full saturation of bentonite using a simplified equivalent homogeneous description of the fractured host rock will tend to be too short.

Abstract This paper describes how four scientific and safety relevant issues have been addressed in special-purpose research laboratories focusing on the geological disposal of high level and long-lived radioactive waste. These are: (a) the effects of heat on the engineered barriers and the geological environment; (b) the geochemical characterization of pore-water in argillaceous rocks; (c) the diffusion and retention of radionuclides; and (d) the full-size sealing of a waste emplacement. They are illustrated by experiments conducted in five underground research laboratories (URLs), three of which are in clay formations (Mol in Belgium, Centre de Meuse–Haute-Marne in France, and Mont Terri Rock Laboratory in Switzerland) and two in granite (Aspö Hard Rock Laboratory in Sweden and Grimsel Test Site in Switzerland). This paper highlights how the various types of experiments are related and how their results have been applied to foster progress. The most complex experiments have revealed artefacts and technical or methodological difficulties associated with interactions among multiple phenomena, the occurrence or intensity of which cannot be analysed by simple models. In turn, these difficulties have prompted experiments targeted at elementary phenomena, thereby encouraging the development of new investigation protocols and monitoring tools. More than 30 years of investigations in special-purpose URLs show the benefits of in-situ experimental programmes in the context of radioactive waste management. The laboratories have opened up avenues for research and advanced knowledge and technology. Thanks to a large component of international cooperation, they have made it possible to mobilize the financial and human resources required for this type of research. They have, above all, shared thoughts and promoted interdisciplinary studies around the same subject. They make common strategies possible at international level.