Posiva -

Low-pH Injection Grout for Deep Repositories. Summary Report from a Co-operation project Between NUMO (Japan), Posiva (Finland) and SKB (Sweden)

Mon, 14 May 2012 10:01:53 +0300

This report summarises results achieved in the joint SKB, Posiva and NUMO project “Injection grout for deep repositories”. The work has been carried out in four sub-projects with SKB and Posiva as responsible for two sub-projects each. This report summarises the original reporting.
Posiva was responsible for the studies on low-pH cementitious grout, while SKB was responsible for the studies on non-cementitious grout. The work was done by literature surveys, laboratory analyses and field tests

A result of the project is that there are both low-pH cementitious material for grouting larger fractures (= 100 µm) and non-cementitious material for grouting smaller fractures (< 100 µm) that will, after further optimisation work, be recommended for grouting of deep repositories.
This project concentrated on the technical development of properties for the low pH grouts. Long-term safety and environmental aspects and durability of materials were preliminarily considered. Continued evaluations have to be carried out.

Host Rock Classification. Phase 3: Proposed Classification System (HRC-System)

Thu, 26 Apr 2012 15:42:52 +0300

This report represents Phase 3 of the Host Rock Classification project, the purpose of which is to develop a rock mass classification system (HRC-system) that can be used to evaluate the suitability of volumes of rock for the disposal of spent nuclear fuel at Olkiluoto. Ultimately the need for a classification system arises from the statements of STUK (the Finnish Radiation and Nuclear Safety Authority) and their external review group, calling for the development of a Finnish rock mass classification scheme for evaluating the suitability of the rock mass for disposal. The HRC-system is specific to Olkiluoto and is not directly applicable to any other site or any disposal concept other than the KBS-3V concept assumed here. It represents a proposed methodology based on current understanding and needs to be tested, developed and updated during the construction of the underground rock characterisation facility, the ONKALO, which will start at Olkiluoto in 2004. The final version of the HRC-system will be approved before the construction of the first deposition tunnels begins.

One of the most important characteristics of the HRC-system is that it considers both the long-term safety of the repository and the constructability of the rock mass. The system also considers separately all three relevant scales of the disposal system, i.e. the repository scale, the tunnel scale and the canister scale. The classification components for each scale have also been divided into two or three separate stages, so that the prediction-outcome approach can be used in the classification process, thereby allowing a preliminary classification to be carried out based on surface data (at the repository scale) or on the data from pilot holes (at the tunnel and canister scales).

The selection of the parameters to be included in the HRC-system is mainly based on the work of Phase 2 of the project, where the most significant rock properties were identified in terms of long-term safety, constructability and the layout and location of the repository. The parameters proposed for the classification at the repository scale include fracture zones, strength/stress ratio, hydraulic conductivity and TDS (total dissolved solids). The parameters proposed for the classification at the tunnel scale include hydraulic conductivity, Q´ and fracture zones and the parameters proposed for the classification at the canister scale include hydraulic conductivity, Q´, fracture zones, fracture width (aperture + filling) and fracture trace length.

The parameter values will be used to determine the suitability classes for the volumes of rock to be classified. The HRC-system includes four suitability classes at the repository and tunnel scales and three suitability classes at the canister scale and the classification process is linked to several important decisions regarding the location and acceptability of many components of the repository at all three scales.

Microstructure, Porosity and Mineralogy Around Fractures in Olkiluoto Bedrock

Mon, 16 Apr 2012 15:44:39 +0300

3D distributions of minerals and porosities were determined for samples that included water-conducting fractures. The analysis of these samples was performed using conventional petrography methods, electron microscopy, C-14-PMMA porosity analysis and X-ray tomography. While X-ray tomography proved to be a very useful method when determining the inner structure of the samples, combining tomography results with those obtained by other methods turned out to be difficult without very careful sample preparation design. It seems that the properties of rock around a water-conducting fracture depend on so many uncorrelated factors that no clear pattern emerged even for rock samples with a given type of fracture. We can conclude, however, that a combination of different analysis methods can be useful and used to infer novel structural information about alteration zones adjacent to fracture surfaces.

Climate scenarios for Olkiluoto on a Time-Scale of 120,000 Years

Mon, 16 Apr 2012 15:35:32 +0300

Posiva Oy is planning to dispose of spent nuclear fuel in a repository, to be constructed at a depth of 400 m in the crystalline bedrock at Olkiluoto, Finland. Planning the storage requires careful consideration of many aspects, including an assessment of long-term repository safety. For estimating possible climate states at Olkiluoto on a time-scale of 120,000 years, we analyze climate simulations of an Earth System Model of Intermediate Complexity (CLIMBER-2) coupled with an ice sheet model (SICOPOLIS).

The simulations into the future clearly show that the onset of the next glaciation is strongly dependent on the Earth’s orbital variations and the atmospheric CO2 concentration. It is evident that due to global warming, the climate of the next centuries will be warmer and wetter than at present. Most likely, due to global warming and low variations in the Earth’s orbit around the sun, the present interglacial will last for at least the next 30,000 years. Further, the future simulations showed that the insolation minima on the Northern Hemisphere 50,000–60,000 and 90,000–100,000 years after the present hold a potential for the onset of the next glaciation. Hence, on a time-scale of 120,000 years, one must take into account climate periods lasting several thousand years having the following features: an interglacial climate, a periglacial climate, a climate with an ice sheet margin near Olkiluoto, a glacial climate with an ice sheet covering Olkiluoto, and a climate with Olkiluoto being depressed below sea level after glaciation due to isostatic depression. Due to the uncertainties related to the evolution of the future climate, it is recommended the simulations into the far future to be used only qualitatively. Quantitative information about glacial climate is achieved from the reconstructions and simulations of the past climate.

Models of Bedrock Surface and Overburden Thickness Over Olkiluoto Island and Nearby Sea Area

Mon, 16 Apr 2012 15:16:23 +0300

In this report, a model of bedrock surface and a model of overburden thickness over the Olkiluoto Island and the nearby sea area are presented. Also in purpose to produce material for biosphere and radionuclide transport modelling, stratigraphy models of different sediment layers were created at two priority areas north and south of the Olkiluoto Island.

The work concentrated on the collection and description of available data of bedrock surface and overburden thickness. Because the information on the bedrock surface and overburden is collected from different sources and is based on a number of types of data the quality and applicability of data sets varies. Consequently also the reliability in different parts of the models varies.

Input data for the bedrock surface and overburden thickness models include 2928 single points and additional outcrops observations (611 polygons) in the modelled area. In addition, the input data include 173 seismic refraction lines (6534 points) and acoustic-seismic sounding lines (26655 points from which 13721 points are located in model area) in the Olkiluoto offshore area.

The average elevation of bedrock surface in area is 2.1 metres above the sea level. The average thickness of overburden is 2.5 metres varying typically between 2 – 4 metres. Thickest overburden covers (approximately 16 m) of terrestrial area are located at the western end of the Olkiluoto Island and in sea basin south of the island.

The Use of Geological Data from Pilot Holes for Predicting FPI (Full Perimeter Intersection) Fractures

Mon, 16 Apr 2012 15:06:03 +0300

Posiva Oy is responsible for preparation of final disposal of spent nuclear fuel in Olkiluoto. The knowledge about existing network of fractures is important for the safety and feasibility of the final repository. The bedrock properties essential for safety case are analyzed in investigations of Rock Suitability Criteria (RSC). One subtask in RSC is avoidance of large (long) fractures adjacent to disposal holes. The long fractures have been defined in tunnel mapping to indicate tunnel cross-cutting fractures (TCF) or full perimeter intersections (FPI).

The purpose for this study was to evaluate the possibility of recognizing FPIs from drill cores by their geological properties. The study was carried out by correlating FPIs mapped from the ONKALO tunnel to the pilot holes logging data with a view of finding out which fracture in the pilot hole corresponds to the FPI in the tunnel. It was also estimated what kind of geological properties does FPIs commonly have in the tunnel and how does these properties differ from the FPI correlated pilot hole fractures. The data sources for this study are the pilot holes from ONK-PH8 to ONK-PH14 and the systematic geological mapping data.

The FPIs used in this study usually follow the general trends of the fracturing in the Olkiluoto bedrock. The fracture surface profiles are principally undulating and a striation can be often seen on the fracture surfaces. The FPIs are frequently moderately to intensely altered with diverse filling mineralogy and thick fracture fillings in comparison to the regular fractures.

The FPI correlated pilot hole fractures have slightly different properties in comparison to the FPIs. These fractures have wider range of different fracture surface profiles and are slightly less altered than the FPIs. Filling mineralogy follows the trends of the FPIs but filling thicknesses are thinner. These differences probably occur because of the variable uncertainties related to the correlation and to the fact that the observed area of a fracture in a pilot hole is much smaller in relation to the observed area of a FPI in the tunnel. This can lead to a situation where the geological properties of a FPI in a pilot hole fracture can be underrepresented.

According to this study there are certain geological properties in a pilot hole fractures that can indicate the presence of a FPI. These properties are:

•   N-S trending sub-vertical or approximately SE dipping sub-horizontal fracture orientation.
•   Undulating and/or slickensided fracture surface profile.
•   In addition to the most common filling minerals (calcite, pyrite, kaolinite and chlorite) illite, clay minerals, epidote, quartz and graphite are present.
•   Joint alteration number (Ja) is = 3.
•   Fracture filling is thicker than in general.

However one should bear in mind that because of the many uncertainties related to FPI predictions from pilot holes it is almost impossible to suggest for certain that some fracture in a pilot hole is or is not a FPI.

Difference Flow and Electrical Conductivity Measurements at the Olkiluoto Site in Eurajoki, Drillholes OL-KR54, OL-KR55, OL-KR55B and OL-KR47B

Mon, 16 Apr 2012 14:40:06 +0300

The Posiva Flow Log, Difference flow method (PFL DIFF) uses a flowmeter that incorporates a flow guide and can be used for relatively quick determinations of hydraulic conductivity and hydraulic head of fractures/fractured zones in drillholes. This report presents the principles of the method and the results of measurements carried out in drillholes OL-KR54, OL-KR55, OL-KR55B and OL-KR47B at the Olkiluoto investigation site between January 2011 and September 2011.

The measuring programme employed was the same in all drillholes. The applied section lengths of the flow guide were either 2 m and 0.5 m. Flow into the drillhole or from the drillhole to the bedrock was measured within the section length. The measurements were carried out in both pumped and natural (i.e. un-pumped) conditions. The transmissivity and hydraulic head of zones were calculated from the flow and pressure results.

The device used includes a sensor for single point resistance (SPR). SPR was measured in connection with the flow measurements.

The electrical conductivity (EC) of fracture-specific water was measured in chosen fractures. Fractures were selected on the basis of the measured flow from fractures into the drillhole.

The drillhole flow (flow along the drillhole) was measured in conjunction with drillhole EC measurements.

The Greenland Analogue Project - Geomodel Version 1 of the Kangerlussuaq Area on Western Greenland

Mon, 16 Apr 2012 13:47:33 +0300

During the 2nd annual Greenland Analogue Project modelling workshop in Toronto, November 2010, the hydrological modellers requested an updated geological map and structural model of the field area around Kangerlussuaq, Western Greenland. This report presents an updated GAP Geomodel which utilizes all available information in order to improve the accuracy of the model, especially beneath the ice-sheet.

The modelling area was divided into two scales: The regional scale area and the site scale area. The site scale refers to the area were surface mapping has been performed, and where two drillholes (DH-GAP01 and DH-GAP03) were drilled during 2009. Geological and topographical maps from GEUS (sub-model 1) and data extracted from the Geophysical map, GEUS, (sub-model 2) were used in the process to develop GAP Geomodel version 1. These two interpretations were independent from each other and in the final stage these sub-models were integrated and developed into GAP Geological model version 1. The integration resulted in a total of 158 lineaments. These lineaments are referred in the final model as deformation zones and faults, where deformation zones are larger features and faults are single fractures indicating some sense of movement. Four different sets of deformation zones and faults were identified in the regional area. The most prominent feature is the ductile/brittle roughly ENE-WSW trending zones crosscutting the whole area; referred as Type 1. Type 2 and Type 3 zones are in general smaller scale than Type 1 and mostly dominated by brittle deformation. The Type 2 system generally trends NW-SE, while the Type 3 system generally trends NE-SW. The Type 4 features are a brittle and roughly N-S orientated younger system, thus crosscutting all other types.

Confirmation and validation of the regional model is based on detailed surface-based examination of fractures within the site area, although the scale is different the same orientations were also identified in the regional lineament interpretation. The site area lineament model is coupled with major tectonic events in Western Greenland to further improve the certainty of our interpretation.

This report describes solely a structural 2-D model and the data produced in this report were developed into a 3-D model that together with hydrological properties serves as basis for the future hydrological modelling within the GAP project, however this work is described in a separate report (Follin et al. 2011).

Modelling End-Glacial Earthquakes at Olkiluoto, Expansion of the 2010 Study

Mon, 16 Apr 2012 13:32:21 +0300

The present report is an extension of Posiva Working Report 2011-13: “Modelling End-glacial Earthquakes at Olkiluoto”. The modelling methodology and most parameter values are identical to those used in that report. The main objective is the same: to obtain conservative estimates of fracture shear displacements induced by end-glacial earthquakes occurring on verified deformation zones at the Olkiluoto site. The remotely activated rock fractures (with their fracture centres positioned at different distances around the potential earthquake fault being considered) are called “target fractures”. As in the previous report, all target fractures were assumed to be perfectly planar and circular with a radius of 75 m.

Compared to the previous study, the result catalogue is more complete. One additional deformation zone (i.e. potential earthquake fault) has been included (BFZ039), whereas one deformation zone that appeared to produce only insignificant target fracture disturbances (BFZ214) is omitted. For each of the three zones considered here (BFZ021, BFZ039, and BFZ100), four models, each with a different orientation of the target fractures surrounding the fault, are analysed. Three of these four sets were included in the previous report, however not as systematically as here where each of the four fracture orientations is tried in all fracture positions.

As in the previous study, seismic moments and moment magnitudes are as high as reasonably possible, given the sizes and orientations of the zones, i.e., the earthquakes release the largest possible amount of strain energy. The strain energy release is restricted only by a low residual fault shear strength applied to suppress post-rupture fault oscillations. Moment magnitudes are: 5.8 (BFZ021), 3.9 (BFZ039) and 4.3 (BFZ100).

For the BFZ100 model, the sensitivity of the results to variations in fracture shear strength is checked. The BFZ021 and BFZ100 models are analyzed for two additional in situ stress orientations, specified to maximize the potential instability of these two deformation zones. For the moment magnitudes, this appeared to have practically no effect.
The new analyses confirm that the results of the previous report can be taken as reasonable upper bound estimates of fracture shear displacements induced by end-glacial earthquakes at the Olkiluoto site. Inclusion of an additional fracture set and all possible combinations of fracture positions and fracture orientations did not increase the maximum induced fracture displacement by more than a few millimetres. The largest induced displacement, 28 mm, was found for a gently-dipping fracture at 100 m distance from the BFZ100 fault. The other deformations zones did not produce induced displacements larger than 12 mm. No fracture belonging to the steeply-dipping sets displaced by more than 6 mm.

Alternative assumptions regarding the present-day in situ stress field and the shear strength of the target fractures did not produce more than marginal, about 3 mm, changes to the results.

Target fracture shear velocities did not exceed 160 mm/s for any fracture in any model. The implications of this finding are not discussed. Here it sufficient to observe that this velocity is significantly lower than the default velocity assumed in the stress-deformation analyses of the buffer-canister system performed to establish the canister damage threshold applied in the Swedish safety analysis (SKB 2010).

Cyprus Natural Analogue Project (CNAP), Phase III Final Report

Mon, 16 Apr 2012 13:22:54 +0300

The CNAP Phase III project was carried out following identification of the requirement to support ongoing laboratory and modelling efforts on the potential reaction of the bentonite buffer with cementitious leachates in the repository EBS. Although it is known that the higher pH (12.5 to 13) leachates from OPC cement will degrade bentonite, it is unclear if this will also be the case for the lower pH (10 to 11) leachates typical of low alkali cements. Ongoing laboratory and URL programmes which are currently investigating this face the obstacle of slow kinetics and the production of short-lived metastable phases, meaning obtaining unambiguous results may take decades. This is exacerbated by the limitations of the thermodynamic databases for minerals of interest to models of bentonite/low alkali cement leachate reaction. It was therefore decided to implement a focussed NA study on bentonite/low alkali cement leachate reaction to provide indications of likely long-term reaction products and reaction pathways to provide feedback on the existing short-term investigations noted above and to ascertain if any critical path R&D needs to be instigated now.

The results of the analyses presented here suggest that there has been very limited alkaline groundwater reaction with the bentonite. This is generally supported by both the geomorphological evidence and the natural decay series data which imply groundwater groundwater/rock interaction in the last 105 a. When integrated with the novel data currently being produced in the BIGRAD project, the CNAP data tend to indicate that any long-term bentonite reaction in low alkali cement leachates is minimal.