Rock Characterisation Facility Research Articles

Mechanical and seismic anisotropy of rocks from the ONKALO underground rock characterization facility

Olkiluoto is an island that was selected as the site for a final nuclear waste disposal facility in Finland. ONKALO underground research facility was constructed for the purpose of rock characterization. A hybrid stress path, incorporating the uncertainties of the near-field stress state estimated for the different Posiva Olkiluoto Spalling Experiment (POSE) phases, was developed as the basis for boundary conditions for a series of true-triaxial tests. Evolution of each principal stress component as a result of excavations and heating of the experimental holes to understand the phenomenon of excavation damage zone (EDZ) development was evaluated. The analysis of the temporal and spatial acoustic emission (AE) activity, construction of 3D damage fracture network images from X-ray CT, and thin section studies performed on tested specimens are presented here. AE events are used to evaluate the chronological occurrence of the damage fracture networks within the induced fractures preferably initiating and propagating within the foliation zones characterized by mica grains, and predominantly avoiding quartz and feldspar grains. Veined gneiss (VGN) samples with a 30° foliation angle relative to the maximum loading direction, and the minimum loading direction perpendicular to the strike of foliation, exhibited the lowest strength, showing shear type fracture initiating parallel to the foliation planes at 55 MPa of axial stress. This value corresponds to the stress state at the POSE experiment hole wall when the first shear type damage was observed to be parallel to the foliation planes. Comparison of the evolution of AE events and seismic velocity measured at the field site for granitic pegmatite (PGR) with its counterpart laboratory specimen was found to be in good agreement. PGR is the strongest member of the rock mass and shows significant AE activity for specimens subjected to the simulated in situ loading without development of macroscale fractures.

Elastoplastic Modelling of an In Situ Concrete Spalling Experiment Using the Ottosen Failure Criterion

An in situ concrete spalling experiment will be carried out in the ONKALO rock characterization facility. The purpose is to establish the failure strength of a thin concrete liner on prestressed rock surface, when the stress states in both rock and concrete are increased by heating. A cylindrical hole 1.5 m in diameter and 7.2 m in depth is reinforced with a 40 mm thin concrete liner from level −3 m down. Eight 6 m long 4 kW electrical heaters are installed around the hole 1 m away. The experiment setup is described and results from predictive numerical modelling are shown. Elastoplastic modelling using the Ottosen failure criterion predicts damage initiation on week 5 and the concrete ultimate strain limit of 0.0035 is exceeded on week 10. The support pressure generated by the liner is 3.2 MPa and the tangential stress of rock is reduced by −33%. In 2D fracture mechanical simulations, the support pressure is 3 MPa and small localized damage occurs after week 3 and damage process slowly continues during week 9 of the heating period. In conclusion, external heating is a potent way of inducing damage and thin concrete liner significantly reduces the amount of damage.

Fracture Mechanics Modelling of an In Situ Concrete Spalling Experiment

During the operation of nuclear waste disposal facilities, some sprayed concrete reinforced underground spaces will be in use for approximately 100 years. During this time of use, the local stress regime will be altered by the radioactive decay heat. The change in the stress state will impose high demands on sprayed concrete, as it may suffer stress damage or lose its adhesion to the rock surface. It is also unclear what kind of support pressure the sprayed concrete layer will apply to the rock. To investigate this, an in situ experiment is planned in the ONKALO underground rock characterization facility at Olkiluoto, Finland. A vertical experimental hole will be concreted, and the surrounding rock mass will be instrumented with heat sources, in order to simulate an increase in the surrounding stress field. The experiment is instrumented with an acoustic emission system for the observation of rock failure and temperature, as well as strain gauges to observe the thermo-mechanical interactive behaviour of the concrete and rock at several levels, in both rock and concrete. A thermo-mechanical fracture mechanics study is necessary for the prediction of the damage before the experiment, in order to plan the experiment and instrumentation, and for generating a proper prediction/outcome study due to the special nature of the in situ experiment. The prediction of acoustic emission patterns is made by Fracod 2D and the model later compared to the actual observed acoustic emissions. The fracture mechanics model will be compared to a COMSOL Multiphysics 3D model to study the geometrical effects along the hole axis.

Immobilization of uranium in biofilm microorganisms exposed to groundwater seeps over granitic rock tunnel walls in Olkiluoto, Finland

In an underground rock characterization facility, the ONKALO tunnel in Finland, massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures at a depth of 70m. In laboratory experiments performed in a flow cell with detached biofilms to study the effect of uranium on the biofilm, uranium was added to the circulating groundwater (CGW) obtained from the fracture feeding the biofilm. The final uranium concentration in the CGW was adjusted to 4.25×10−5M, in the range expected from a leaking spent nuclear fuel (SNF) canister in a future underground repository. The effects were investigated using microelectrodes to measure pH and Eh, time-resolved laser fluorescence spectroscopy (TRLFS), energy-filtered transmission electron microscopy (EF-TEM), and electron energy-loss spectroscopy (EELS) studies and thermodynamic calculations were utilized as well. The results indicated that the studied biofilms constituted their own microenvironments, which differed significantly from that of the CGW. A pH of 5.37 was recorded inside the biofilm, approximately 3.5units lower than the pH observed in the CGW, due to sulfide oxidation to sulfuric acid in the biofilm. Similarly, the Eh of +73mV inside the biofilm was approximately 420mV lower than the Eh measured in the CGW. Adding uranium increased the pH in the biofilm to 7.27 and reduced the Eh to −164mV. The changes of Eh and pH influenced the bioavailability of uranium, since microbial metabolic processes are sensitive to metals and their speciation. EF-TEM investigations indicated that uranium in the biofilm was immobilized intracellularly in microorganisms by the formation of metabolically mediated uranyl phosphate, similar to needle-shaped autunite (Ca[UO2]2[PO4]2·2–6H2O) or meta-autunite (Ca[UO2]2[PO4]2·10–12H2O). In contrast, TRLFS studies of the contaminated CGW identified aqueous uranium carbonate species, likely (Ca2UO2[CO3]3), formed due to the high concentration of carbonate in the CGW. The results agreed with thermodynamic calculations of the theoretically predominant field of uranium species, formed in the uranium-contaminated CGW at the measured geochemical parameters.This investigation clearly demonstrated that biological systems must be considered as a part of natural systems that can significantly influence radionuclide behavior. The results improve our understanding of the mechanisms of biofilm response to radionuclides in relation to safety assessments of SNF repositories.

Geoscience and high-level nuclear waste disposal: the Nordic scene

In Norden, two countries, Sweden and Finland, are actively engaged in site investigations for the location of deep repositories for spent nuclear fuel from powerproducing nuclear reactors. These investigations are being carried out in crystalline rocks of the Fennoscandian Shield. In Sweden, a long history of site selection has led to the identification and investigation of two sites, Forsmark and Laxemar/Simpevarp, based on a strategy of combining favourable bedrock with consent by the local population. Surface-based geoscientific investigations of the two candidates, with extensive deep drilling, are now drawing to a close. A proposal as to which of the sites would be most suitable for the development of a deep repository will be submitted to the governmental regulatory authorities in 2009. In Finland, the site selection process was shorter and less politically controversial, and led to a Decision in Principle by the Finnish parliament, in May 2001, to develop a deep repository at the Olkiluoto site. The access tunnel to an underground rock characterisation facility at 400-500 m depth is at present under construction, accompanied by extensive geoscientific investigations in the subsurface. An application for a construction licence for a deep repository will be submitted in 2012. Although all sites are located in Precambrian crystalline rocks, the Swedish sites both lie in relatively homogeneous granitic rocks, whilst the Finnish site is located in an heterogeneous migmatite complex. The Nordic approach to high-level nuclear waste disposal in crystalline rock will be the theme of a Topical Symposium at the 33rd International Geological Congress at Oslo, in August 2008, and the three sites mentioned above will be the focus of Congress Excursion no. 14.

Further Steps Towards Licensing: Underground Characterisation Started for the Spent Fuel Repository in Finland

ABSTRACTPursuant to the Decision-in-Principle of 2001 the Finnish programme for geologic disposal of spent fuel has now moved to the phase of underground characterisation of the repository site. The main objective of this programme phase is to confirm – or refute – the suitability of the Olkiluoto site by investigations conducted underground at the actual depth of the repository. The construction work of the access tunnel to the rock characterisation facility (ONKALO) started in the late summer of 2004. The site research and investigations work aims at the maturity needed for submission of the application for construction license of the actual repository in 2012. This requires, however, that also the technology has reached the maturity needed. The design and technical plans form the necessary platform for the development of the safety case for spent fuel disposal. A plan, “road map”, has been produced for the portfolio of reports that should demonstrate the safety of disposal as required by the criteria set by the government and further detailed by the safety authority, STUK.

The problem of the UK's radioactive waste: what have we learnt?

The UK has significant holdings of long lived radioactive waste that will remain potentially hazardous for many thousands of years. Previous attempts to dispose of these wastes have ended in failure. The most recent attempt ended with a refusal from the Secretary of State for the Environment to allow the construction of an underground rock characterisation facility (RCF ) close to the Sellafield nuclear plant. The wastes still exist of course. If we are to avoid passing this waste legacy on to future generations, the need for a long term management solution remains. Such a solution may or may not include an element of disposal. In consultation with other parties, Nirex has reviewed the events leading up to the RCF decision in the light of other countries' experience and recent academic research. This review has shown that if a widely acceptable solution is to be found, there will need to be a widespread consensus on three key issues, namely the process through which any solution is reached, the structure of the organisations charged with overseeing and implementing the solution, and the behaviour of those organisations and the individuals within them.

Prediction of the hydro-mechanical response during shaft sinking for the proposed Nirex Rock Characterisation Facility near Sellafield, Cumbria, United Kingdom

Abstract The coupled hydro-mechanical responses in the fractured volcaniclastic rocks of the Borrowdale Volcanic Group, Sellafield, Cumbria, to a long-term pump test and the proposed shaft sinking phase of Nirex's Rock Characterisation Facility was studied by research teams under the auspices of the second phase of DECOVALEX project. This paper discusses the background and objectives of the study and provides a brief summary of the results and major scientific and logistical lessons learnt.

NIREX Transport Activities since Rejection of the Rock Characterisation Facility Planning Application

AbstractThe application by Nirex to build an underground Rock Characterisation Facility, was rejected by the Secretary of State on 17 March 1997. This decision has caused Nirex to reconsider its forward programme for the development of an underground disposal facility for intermediate level waste. This paper describes the transport related activities being undertaken by Nirex since that date.

The Importance of Waste Packaging Advice Following Rejection of the Nirex RCF Planning Application

The decision to reject the Nirex application to build the Rock Characterisation Facility at Longlands Farm in Cumbria will inevitably lead to a delay in the development of the UK deep repository for intermediate level waste. This delay, however, has not had a major impact on the Nirex approach to waste packaging as the strategy has always been to ensure that Waste Package Specifications are not specific to a particular site or design. In the absence of a finalised repository site, design or associated safety cases, Nirex has not been in a position to issue final Waste Acceptance Criteria. Nirex has instead produced and issued a suite of waste package specifications and guidance documentation which define packaging standards and which give guidance to customers on the form of packaging which will be consistent with developing plans for safe transport, handling, storage and disposal. The documentation is not based on a specific repository design or safety case, but is founded on design concepts and safety assessments for generic transport and underground repository systems. Many customers are now developing waste management strategies that involve the retrieval and packaging of waste in a form that will be suitable for interim storage and deep disposal. In such situations Nirex will assist customers by the provision of waste packaging advice, and if proposals are consistent with plans for transport, handling, storage and disposal, by the issue of a Letter of Comfort. Experience has shown that there is value in seeking Nirex advice at three stages in the development of a waste packaging project: at the conceptual stage, at the pre-commitment stage and finally prior to active commissioning. Nirex advice will enable agreements to be reached on key issues such as waste package design, wasteform and data recording. It will identify areas of uncertainty or where further evidence and/or R&D may be required and will ensure that satisfactory QA systems are in place prior to plant operations. Assuming that there are no outstanding issues, Nirex will issue a final Letter of Comfort. This process has been recognised as being of value by Nirex, regulators and customers. The Nirex strategy to define packaging standards against generic repository and transport system concepts has been shown to be robust and continues to provide an appropriate standard for waste packaging.

Recent advances in the understanding of the geology of west Cumbria: II. Convenors’ review

In October 1993, the Yorkshire Geological Society held a full-day meeting with the title ‘Advances in west Cumbrian geology resulting from the Nirex investigations around Sellafield’ (Holliday & Rees 1994). The meeting presented results from the, then ongoing, geoscience investigations by United Kingdom Nirex Limited (Nirex) into whether the Sellafield area in west Cumbria could be suitable as a repository of intermediate and some low level radioactive waste. The presentations at the meeting, and other related papers, formed the subject of a thematic part of the Society’s Proceedings (Vol. 50, part 1). Since then several significant events relevant to the Nirex investigations have taken place (Kelling & Knill 1997). In December 1994, Cumbria County Council rejected Nirex’s application to construct an underground research laboratory, a Rock Characterization Facility (RCF), within the concealed rocks of the Borrowdale Volcanic Group (BVG), about 2.5 km inland of Sellafield, beneath Longlands Farm, near Gosforth. As a result of Nirex’s appeal against this decision, a Public Inquiry was held in Cleator Moor, between September 1995 and February 1996. In March 1997, after consideration of the Inquiry Inspector’s report, the Secretary of State for the Environment rejected Nirex’s appeal against the County Council’s decision. Nirex decided not to appeal against this decision, and the Sellafield investigations have been wound down. Since 1993, the geoscientific investigations at Sellafield advanced significantly and, prior to the Secretary of State’s decision, a second meeting devoted to the geology of west Cumbria was arranged by the Society in order to allow ...

The work of a radioactive waste management watchdog The work of the Radioactive Waste Management Advisory Committee

This paper traces the origins and development of the Radioactive Waste Management Advisory Committee (RWMAC), an independent committee of experts charged with giving advice to Government on issues relating to the management of civil radioactive waste. It focuses on the constitution of the committee and its working methods and the way in which these are arranged to reflect RWMAC's independence. In describing the committee's work, particular attention is paid to the deep disposal strategy for intermediate level waste. There is discussion of RWMAC's advice on the need for openness and transparency and the options available to the Government following rejection of the Nirex planning application for a Rock Characterisation Facility (RCF) at Longlands Farm, near Sellafield. However, as consideration of the committee's 1998 work programme shows, its remit extends much wider than issues associated with the disposal of radioactive waste.

Public perception of radioactive waste

The failure of Nirex's application to construct a Rock Characterisation Facility at Sellafield has led to some rethinking on the public's perception of the issues involved in radioactive waste management. This paper proposes that the importance of creating the right public impression has been grossly underestimated in the past because science has been left to the scientists. It has been assumed that a scientific consensus will be achieved and that the public will accept its findings. The reality is that the public are far more sophisticated in their perception of the issues. The paper goes on to explore the factors shaping public perception and proposes some possible solutions to help the public buy into the problem.

Public perception of radioactive waste

The failure of Nirex's application to construct a Rock Characterisation Facility at Sellafield has led to some rethinking on the public's perception of the issues involved in radioactive waste management. This paper proposes that the importance of creating the right public impression has been grossly underestimated in the past because science has been left to the scientists. It has been assumed that a scientific consensus will be achieved and that the public will accept its findings. The reality is that the public are far more sophisticated in their perception of the issues. The paper goes on to explore the factors shaping public perception and proposes some possible solutions to help the public buy into the problem.

The UK rock characterization programme

The objective of the Nirex Science Programme is to evaluate the post-closure safety performance of a deep repository for intermediate level wastes (both long and short lived) and some low level wastes at a site near Sellafield in West Cumbria. The extensive surface-based site characterization programme, complemented by research and assessment studies, has established the potential suitability of the Sellafield site for the deep repository. However, a stage of underground investigations, the Rock Characterization Facility, is needed in order to establish the high level of confidence necessary to underpin a decision on whether to propose development of a repository, and subsequently a decision by the regulators to authorize commencement of disposal operations in the repository when it is constructed. The Rock Characterization Facility will be developed in three phases, providing a scientific programme lasting around ten years. It will address three key areas of uncertainty as follows: (1) groundwater flow and radionuclide transport; (2) natural and induced changes to the geological barrier; (3) design and construction of the repository. The nature of these uncertainties, the way in which underground investigations enable us to resolve them, and the design of the Rock Characterization Facility and its experimental programme to deliver the required information to resolve these uncertainties are described in this paper.

The International Legal Position on Transboundary Shipments of Radioactive Waste

AbstractThe recent decision not to grant planning permission for construction of a Rock Characterisation Facility near Sellafield has reopened the question of long-term radioactive waste disposal policy in the UK. One possible solution would be the construction and operation of a small number of international radioactive waste disposal facilities, taking waste from several countries. Such an approach would allow pooling of international expertise; would allow the choice of excellent sites from geological and demographical standpoints; and may be economically attractive depending on economies of scale. However, the approach would also increase the amount of waste transport, and may reduce the pressure on producers to reduce the volumes of waste arising. This paper traces the development of international legal attitudes to transboundary transport of radioactive and other hazardous waste. It concludes that as international law now stands it would be very difficult to establish a network of international wast...

The geology and hydrogeology of Sellafield: an overview

Abstract Nirex is responsible for providing and managing a national facility for solid intermediate-level and low-level radioactive waste. Geological and hydrogeological investigations have been in progress at Sellafield in west Cumbria since 1989 aimed at determining whether or not the site is suitable for such a deep repository. Geological investigations have included the drilling of 20 deep boreholes with over 20000 metres of drilling, together with almost 2000 line kilometres of seismic surveys and over 8000 line kilometres of airborne geophysical surveys. Hydrogeological testing and groundwater sampling and testing have provided additional information on the ground conditions at the site. The results from the investigations show that the Borrowdale Volcanic Group of rocks, the top surface of which is 400–600 m beneath the site at Sellafield, holds good promise as an eventual location for the repository. Further investigations are required before the suitability of the site can be confirmed. These additional investigations will include the construction of an underground rock-characterization facility for which Nirex applied for planning permission to construct in 1994. The investigations carried out to date have defined the subsurface structure of the area and have defined a stratigraphic subdivision of the Borrowdale Volcanic Group. Groundwater flow within the volcanic rocks has been shown to be occurring through a limited number of fractures and preliminary work has been undertaken to characterize these hydrogeologically significant fractures. Hydrogeochemical studies have begun to characterize the groundwater types and preliminary results have indicated that the groundwaters at depth are saline with residence times in excess of tens of thousands of years.

Deep disposal of radioactive waste in the United Kingdom / Tieflagerung radioaktiver Abfälle im Vereinigten Königreich

This paper summarises the progress that is being made with the development of deep disposal of intermediate- and low-level radioactive wastes in the United Kingdom. Following an extensive site selection exercise, a comprehensive programme of geological and hydro geological characterisation has been carried out at Sellafield in North West England since 1989 to evaluate its suitability to host a deep repository. This pro gramme has in dicated that the site shows good promise but a substantial amount of further work is required. The next major step is a rock characterisation facility, for which preparatory work has already begun