Browsing by Subject "Olkiluoto"
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(2019)Tiivistelmä/Referat – Abstract This study investigates temperature data that Posiva Oy has from the Olkiluoto and ONKALO® sites. The aim of the study was to create a unifying data classification for the existing temperature measurements, give an estimate of the initial undisturbed bedrock temperature and temperature gradient and model the temperature profiles in 3D. The thermal related issues, which the repository will undergo once in operating are significant and have fundamental contribution to the evolution of the repository, creating a need in such a study. Posiva Oy has temperature data obtained with four main methods; Geophysical drillhole loggings, Posiva flow log (PFL) measurements, thermal properties (TERO) measurements and Antares measurements. The data classification was carried out by creating a platform of quality aspects affecting the measurements. The classification was then applied for all the available data by inspecting the measurement specifics of each configuration and by observing the temperature/depth profiles with WellCad software. According to the specifics of each individual measurement the data was classified into three groups: A= the best data, recommended for further use, and which fulfils all quality criteria, B= data that should be used with reservation and which only partly fulfils quality criteria, and C= unusable data. Only data that showed no major disturbance within the temperature/depth profile (class A or B) were used in this study. All the temperature/depth data was corrected to the true vertical depth. The initial undisturbed average temperature of Olkiluoto bedrock at the deposition depth of 412 m and the temperature gradient, according to the geophysical measurements, PFL measurements (without pumping), TERO measurements and Antares measurements were found to be 10.93 ± 0.09°C and 1.47°C/100m, 10.85 ± 0.02°C and 1.43°C/100m, 10.60 ± 0.08°C and 1.65°C/100m, and 10.75°C and 1.39°C/100m, respectively. The 3D layer models presented in this study were generated by using Leapfrog Geo software. From the model a 10.5 – 12°C temperature range was obtained for the deposition depth of 412 – 432 m. The models indicated clear temperature anomalies in the volume of the repository. These anomalies showed relationship between the location of the major brittle fault zones (BFZ) of Olkiluoto island. Not all observed anomalies could be explained by a possible cause. Uncertainties within the modelling phase should be taken into consideration in further interpretations. By combining an up-to-date geological model and hydraulic model of the area to the temperature models presented here, a better understanding of the temperature anomalies and a clearer over all understanding of the thermal conditions of the planned disposal location will be achieved. Based on this study a uniform classification improves the usability of data and leads into a better understanding of the possibilities and weaknesses within it. The initial bedrock temperature and the temperature gradient in Olkiluoto present thermally a relatively uniform formation. The estimates of the initial bedrock temperatures and the temperature gradient presented in this study, endorse previous estimates. Presenting the classified temperature data in 3D format generated good results in the light of thermal dimensioning of Olkiluoto by showing distinct relationships between previously created brittle fault zone (fracture zone) models. The views and opinions presented here are those of the author, and do not necessarily reflect the views of Posiva.
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(2020)NMR Services Australia (NMRSA) Pty Ltd has developed a Borehole Magnetic Resonance (BMR) tool which is based on the principles of nuclear magnetic resonance (NMR). Drillhole NMR tools have been used mostly in sedimentary environments for oil and gas exploration while applications in hard, heterogeneous, crystalline bedrock are still lacking. This study aims to test the BMR method in a hard rock environment, and for determining hydrogeological parameters in the spent nuclear fuel disposal site, the Olkiluoto island. Essentially, the objective is to design an optimal BMR data processing workflow and calibrate the estimated hydrogeological parameters, currently optimized for data from sedimentary environments, to suit the crystalline bedrock. For testing the BMR method in hard, crystalline bedrock, Posiva Oy, the Finnish expert organization responsible of spent nuclear fuel disposal, made test measurements in the drillholes of the spent nuclear fuel repository site, island of Olkiluoto. The collected data was processed with WellCAD software using additional NMR module. The BMR tool derives T2 distribution (representing pore size distribution), total porosity, bound water and moveable water volumes and permeability calculated with two different models. Some processing parameters (main/burst sequence, moving averages, temperature gradient, cutoff values) were tested and adjusted to fit into crystalline bedrock. Magnetizing material of the surface environment strongly disturbed the uppermost ~20.0 m portions of the measurement data. Some noise was encountered also deep in bedrock, which was cut away from the signal. A list of criteria was created for recognizing noise. The BMR data was compared with other drillhole data acquired by Posiva, i.e. fracture and lithology logs, seismic velocities and hydrogeological measurements. It was observed that the T2 distribution and total porosity correlate rather well to logged fractures and seismic velocities. Lithological variations did not correlate to BMR consistently, mostly because of the strong dependency on fracturing. Permeabilities were compared to earlier conducted hydrogeological measurements, with an intention to calibrate the permeability calculation models. However, this proved to be challenging due to the significant differences of the BMR method and conventional hydrogeological measurements. Preferably, the permeability models should be calibrated by laboratory calibration of the drillhole core, and possibly a new permeability model suitable for crystalline bedrock should be created.
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(2020)As a part of constructing the upcoming repository for spent nuclear fuel ONKALO®, Posiva Oy is investigating the hydrogeological structures of Olkiluoto bedrock. Posiva Flow Log (PFL) drillhole measurements are an important part in characterization of bedrock’s hydraulic properties. The measurements are conducted both from the surface and in the study site of ONKALO tunnel network. Results are used widely at the site from the planning of construction to the water conducting fracture characterization. PFL equipment are capable of measuring groundwater flow originating from a single fracture which enables small scale detection of transmissive fractures in bedrock. Equipment measures temperature variations in a water flow inside an isolated test section to determine the flow rate. Several other equipment for groundwater flow measurement are introduced to highlight the accuracy of PFL. Fractures measured with PFL DIFF were 3D modelled in twelve ONKALO pilot holes (ONK-PH13-20, ONK-PH23, ONK-PH26 and ONK-PH28-29) using FracMan software suitable for fracture network modelling. 3D model described the fracture locations with fracture orientation and pilot hole transmissive fracture traces projected to tunnel walls. Brittle fault zone intersection between the chosen pilot holes were also modelled. Three of the pilot holes (ONK-PH23, ONK-PH28 and ONK-PH29) were selected for the fracture correlation. Pilot hole transmissive fractures were connected with tunnel wall water leaking fractures located with systematic mapping and water leakage mapping. Criteria for connecting the fractures were fracture location, water leakage and fracture orientation. Structure intersections with brittle fault zones were studied individually for each pilot hole. 433 meters of ONKALO tunnels were included in the correlation with total 20 of pilot hole transmissive fractures and 18 tunnel wall water leaking fractures according to systematic mapping. 100 % of ONK-PH23, 75 % of ONK-PH28 and 16,7 % of ONK-PH29 pilot hole transmissive fractures were correlated with tunnel wall water leakages in the corresponding depths. Counterparts were found for nine fractures of total 20 studied fractures based on the listed attributes. Fracture correlation was unsuccessful with 11 of the observed transmissive fractures. Study produced new data for the possible fracture correlations and hydraulic connections were produced in the pilot hole areas. Views and opinions described in this thesis are interpretation of the author and do not necessarily represent Posiva’s views.
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(2021)Kappa-parameter (κ) is used to estimate the decay of seismic spectral amplitudes with frequency and is the sum of regional kappa (κr) and site-specific kappa (κ0). The site-specific kappa (κ0) parameter in Olkiluoto (Southwestern Finland) is generally small, approximately 0.002 to 0.004. These values, although smaller, are in the same range that have been found in Eastern North America, where kappa is around 0.006. In Western North America kappa is around 0.04. In Europe, e.g., in alpine region, kappa value is around 0.025. The kappa-value was studied by analysing microearthquake recordings gathered by Posiva Oy’s seismic monitoring network from 2016 to 2019. From these microearthquakes 51 microearthquakes were selected and used in the analysis. All these microearthquakes occurred relatively close to the monitoring stations, from tens of meters to few hundred meters. Each of the events were detected by multiple sensors and the total number of microearthquake registrations used in this study was 297. From these recordings the κ0 was calculated for each component (two horizontal and one vertical). Total number of calculated κ0 values was 473. The kappa-method used was the original introduced by Anderson and Hough in 1984. Besides using earthquake data, the site-specific kappa was also calculated from excavation blasts in Olkiluoto for comparison. Blasting related kappa was smaller than the one calculated from microearthquakes, with average values between 0.0012 and 0.0017. The number of blasts used to calculate κ0 was quite small and the results may not be statistically relevant. Results are in line with similar study areas around the world – harder rock has lower κ0 values
Now showing items 1-4 of 4