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Helsinki, Finland

Kemppainen K.,Posiva Oy | Hakala M.,Nokia Inc. | Johansson E.,Saanio and Riekkola Oy | Kuula H.,WSP Finland Oy | Hudson J.A.,Imperial College London
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012

As part of the preparations for the design of an underground repository for radioactive waste at Posiva's site on the west coast of Finland, there has been considerable site investigation work. One of the key elements of this work has been the estimation of the in situ stress field and determination of the mechanical properties of the crystalline rocks present. The stress field is required as the boundary condition for numerical modelling and to determine a suitable orientation for the repository tunnels. The mechanical rock properties are required, inter alia, to establish whether there is any potential for rock spalling at the ca. 400-450 m anticipated depth of the repository. A key aspect of the analysis is the understanding of the in situ spalling strength in order to be able to predict the spalling potential, not only during deposition tunnel and deposition hole excavation but also in the longer term when the rock mass is subjected to canister heating up to temperatures close to 60°C. The in situ spalling strength is of the order of 60% of the uniaxial compressive strength. Accordingly, an in situ rock mechanics experiment has been designed and conducted in a niche tunnel off the main ONKALO ramp at the Olkiluoto site in Finland. The experiment has the acronym POSE: Posiva's Olkiluoto Spalling Experiment. The experiment has involved the drilling of two closely located full-scale simulated deposition holes, 1.524m in diameter, which concentrate the in situ stress and enable rock spalling to be observed at close hand. In addition, heaters have been used to simulate the rock temperature increase due to radioactive canister heat generation, further altering the in situ stress field. The preliminary POSE experimental results and the thermo-mechanical simulations are illustrated and presented in this paper. © 2012 Taylor & Francis Group, London. Source

Lusa M.,University of Helsinki | Lempinen J.,University of Helsinki | Ahola H.,University of Helsinki | Soderlund M.,University of Helsinki | And 3 more authors.
Radiochimica Acta | Year: 2014

Soil samples from three forest soil pits were examined down to a depth of approximately three metres using 1M ammonium acetate extraction and microwave-Assisted extraction with concentrated nitric acid (HNO3), to study the binding of cesium (Cs) at Olkiluoto Island, southern Finland. Ammonium acetate was used to extract the readily exchangeable Cs fractions roughly representing the Cs fraction in soil which is available for plants. Microwave-Assisted HNO3 extraction dissolves various minerals, e.g. carbonates, most sulphides, arsenides, selenides, phosphates, molybdates, sulphates, iron (Fe) and manganese (Mn) oxides and some silicates (olivine, biotite, zeolite), and reflects the total Cs concentrations. Cs was mostly found in the strongly bound fraction obtained through HNO3 extraction. The average Cs concentrations found in this fraction were 3.53±0.30mg/kg (d.w.), 3.06±1.86mg/kg (d.w.) and 1.83±0.42mg/kg (d.w.) in the three soil pits, respectively. The average exchangeable Cs found in the ammonium acetate extraction in all three sampling pits was 0.015±0.008mg/kg (d.w.). In addition, Cs concentrations in the soil solution were determined and in situ distribution coefficients (Kd) for Cs were calculated. Furthermore, the in situ Kd data was compared with the Cs K d data obtained using the model batch experiments. The in situ K d values were observed to fairly well follow the trend of batch sorption data with respect to soil depth, but on average the batch distribution coefficients were almost an order of magnitude higher than the in situ K d data. In situ Cs sorption data could be satisfactory fitted with the Langmuir sorption isotherm, but the Freundlich isotherm failed to fit the data. Finally, distribution coefficients were calculated by an ion exchange approach using soil solution data, the cation exchange capacity (CEC) as well as Cs to sodium (Na) and Cs to potassium (K) ion exchange selectivity coefficients. The calculated distribution coefficients corresponded well with the in situ distribution coefficient values. © 2014 Walter de Gruyter Berlin/Boston. Source

Uotinen L.K.T.,Aalto University | Salo O.,Saanio and Riekkola Oy | Rinne M.,Aalto University
Rock Characterisation, Modelling and Engineering Design Methods - Proceedings of the 3rd ISRM SINOROCK 2013 Symposium | Year: 2013

Yield-Line Theory (YLT) has been in wide spread use since the 1960's. YLT allows determining of the upper-bound bending resistance of reinforced concrete slabs using the concept of virtual work. YLT can be used for two purposes in the design of sprayed concrete support: the determination of quality assurance demands for the sprayed concrete or in the design of adequate sprayed concrete layer thickness against a bending failure. The square slab energy absorption test (EN 14488-5) and the round panel flexural toughness test (ASTM C1550-12a) are used. Solutions for both tests are given and conversion equations are derived. Testing results produced during normal quality assurance testing process in Länsimetro project (Finland) are shown for comparison. Finally, the merits and draw-backs of the test types are discussed. © 2013 Taylor & Francis Group. Source

Sedighi M.,University of Cardiff | Masum S.A.,University of Cardiff | Thomas H.R.,University of Cardiff | Bennett D.P.,University of Cardiff | And 2 more authors.
3rd International Conference on Computational Methods for Thermal Problems, ThermaComp 2014 | Year: 2014

This paper presents the results of an investigation into the thermal behaviour of a site proposed for the deep geological disposal of high level radioactive waste in Finland. Temperature data, collected from 57 boreholes at depths of up to 1000m have been studied. The thermal behaviour of the rock at the site, which is based in ONKALO, is discussed. The results achieved provide an improved understanding of in-situ rock thermal conditions at the site; information which is required for the long term safety assessment of the disposal option. Source

Hudson J.A.,Imperial College London | Cosgrove J.W.,Imperial College London | Kemppainen K.,Posiva Oy | Johansson E.,Saanio and Riekkola Oy
Engineering Geology | Year: 2011

Brittle deformation zones at the Olkiluoto nuclear repository site in western Finland play critical roles in the strength and hydrology of the host rock mass. We present a procedure implemented there for incorporating information on deformation zones obtained through boreholes into quantitative engineering design. First, ductile and brittle deformation zones are classified based on their characteristics in drillhole cores as brittle joint clusters, brittle fault zones, or semi-brittle fault zones, with an awareness of the geologic processes that caused the zones to develop as they did. Next, it is shown that the mechanical properties of the brittle deformation zones can be calculated by one of several methods, each of which has advantages and disadvantages. The site geology must be kept in mind at all stages to arrive at meaningful estimates of the mechanical properties of the deformation zones. © 2010 Elsevier B.V. Source

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