Preliminary Site Description Simpevarp Subarea – Version 1.2
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R-05-08 Preliminary site description Simpevarp subarea – version 1.2 Svensk Kärnbränslehantering AB April 2005 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 5864 SE-102 40 Stockholm Sweden Tel 08-459 84 00 +46 8 459 84 00 Fax 08-661 57 19 +46 8 661 57 19 ISSN 1402-3091 SKB Rapport R-05-08 Preliminary site description Simpevarp subarea – version 1.2 Svensk Kärnbränslehantering AB April 2005 A pdf version of this document can be downloaded from www.skb.se Preface The Swedish Nuclear Fuel and Waste Management Company (SKB) is undertaking site characterisation at two different locations, the Forsmark and Simpevarp areas, with the objective of siting a geological repository for spent nuclear fuel. An integrated component in the characterisation work is the development of a site descriptive model that constitutes a description of the site and its regional setting, covering the current state of the geosphere and the biosphere as well as those ongoing natural processes that affect their long-term evolution. The Simpevarp candidate area consists of two subareas, named the Laxemar subarea and the Simpevarp subarea, that were prioritised for further investigations. The present report documents the site descriptive modelling activities (version 1.2) for the Simpevarp subarea. The overall objectives of the version 1.2 site descriptive modelling are to produce and document an integrated description of the site and its regional environments based on the site-specific data available from the initial site investigations and to give recommendations on continued investigations. The modelling work is based on primary data, i.e. quality-assured, geoscientific and ecological field data available in the SKB databases SICADA and GIS, available April 1, 2004. The work has been conducted by a project group and associated discipline-specific working groups. The members of the project group represent the disciplines of geology, rock mechanics, thermal properties, hydrogeology, hydrogeochemistry, transport properties and surface ecosystems (including overburden, surface hydrogeochemistry and hydrology). In addition, some group members have specific qualifications of importance in this type of project e.g. expertise in RVS (Rock Visualisation System) modelling, GIS-modelling and in statistical data analysis. The overall strategy to achieve a site description is to develop discipline-specific models by interpretation and analyses of the primary data. The different discipline-specific models are then integrated into a site description. Methodologies for developing the discipline-specific models are documented in methodology reports or strategy reports. A forum for technical coordination between the sites/projects sees to that the methodology is applied as intended and developed if necessary. The forum consists of specialists in each field as well as the project leaders of both modelling projects. The following individuals and expert groups contributed to the project and/or to the report: • Anders Winberg – project leader and editor, • Karl-Erik Almén, Henrik Ask, Roy Stanfors – investigation data, • Carl-Henric Wahlgren, Jan Hermanson, Philip Curtis, Ola Forssberg, Paul La Pointe, Eva-Lena Tullborg – geology, • Eva Hakami, Flavio Lanaro, Isabelle Olofsson, Anders Fredriksson – rock mechanics, • Jan Sundberg and co-workers – thermal properties, • Ingvar Rhén, Sven Follin, Lee Hartley and the members of the HydroNET Group – hydrogeology, • Marcus Laaksoharju and the members of the HAG group – hydrogeochemistry, • Sten Berglund, Johan Byegård and co-workers – transport properties, • Tobias Lindborg and the members of the SurfaceNET group – surface ecosystems (including overburden), • Johan Andersson – confidence assessment, • Fredrik Hartz and Anders Lindblom – production of maps and figures. The report has been reviewed by the following members of SKB’s international Site Investigation Expert Review Group (SIERG): Per-Eric Ahlström (Chairman); Jordi Bruno (Enviros, Spain); John Hudson (Rock Engineering Consultants, UK); Ivars Neretnieks (Royal Institute of Technology, Sweden); Lars Söderberg (SKB); Mike Thorne (Mike Thorne and Associates Ltd, UK); Gunnar Gustafson (Chalmers University); Roland Pusch (GeoDevelopment AB). The group provided many valuable comments and suggestions for this work and also for future work. The latter group is not to be held responsible for any remaining shortcomings of the report. Additional review comments on the geological models were also provided by Raymond Munier (SKB). Anders Ström Site Investigations – Analysis Summary The objectives of the version 1.2 site descriptive modelling (SDM) of the Simpevarp subarea are to: produce and document an integrated description of the site and its regional environments based on the site-specific data available from the initial site investigations and to give recommendations on continued investigations on a continuous basis. The modelling work is based on primary data available at the time of the data freeze for Simpevarp 1.2, April 1, 2004. The local scale model area (24 km2) for the Simpevarp 1.2 modelling encompasses both the Simpevarp and Laxemar subareas. The local model area is located in the centre of a regional scale model area (273 km2). The surface data is in terms of geology essentially equitable to those used for SDM Simpevarp 1.1 and consequently large uncertainties still remain for the Laxemar subarea. The borehole data available for Simpevarp 1.2 are foremost related to the Simpevarp subarea where there are four new cored boreholes (KSH01A/B, KSH02, KSH03A/B and KAV04), new complementary data from two existing boreholes, KAV01 and KLX02, and three percussion boreholes positioned on the Simpevarp peninsula (HSH01–HSH03). Model results Surface ecosystem models in terms of pools and fluxes of carbon have been developed for the terrestrial (e.g. plants and animals) and limnic (e.g. algae and fish) systems using the Lake Frisksjön drainage area. Furthermore, a first marine ecosystem model has been developed for the Basin Borholmsfjärden. The parts of the Simpevarp subarea located above sea level are largely outlined by the Simpevarp peninsula and the Hålö and Ävrö islands. The investigated area features a relatively flat topography (c. 0.4% topographical gradient), which largely reflects the surface of the underlying bedrock surface, and is also characterised by a high degree of bedrock exposures (38%). Till is the dominant Quaternary deposit which covers about 35% of the subarea. Three principal lithological domains have been defined in the subarea, an A domain that is dominated by the Ävrö granite and which dominates on the island of Ävrö, Hålö and the northern parts of the peninsula, a domain B that is dominated by the fine-grained dioritoid and dominates the Simpevarp peninsula, a C domain that is characterised by a mixture of of Ävrö granite and quartz monzodiorite on the cape of the peninsula. A fourth domain is made up a few scattered domains of diorite to gabbro. The ore potential in the area is considered negligible, with a real potential only for quarrying of building- and ornamental stone associated with the Götemar and Uthammar granite intrusions to the north and south of the investigated area, respectively. In total, 22 deformation zones with high confidence of occurrence have been interpreted in the local scale model area. The understanding of the interpreted deformation zones of the Simpevarp subarea is considered adequate to make a preliminary assessment of available storage volumes for a deep repository. The two most important and volume-delineating deformation zones are ZSMNE012A, which trends north of the islands of Hålö and Ävrö, dipping towards the southeast under the Simpevarp peninsula, and ZSMNE024A which strikes northeast along the coast of the Ävrö island and the Simpevarp peninsula. The remaining uncertainty in the developed deformation zone model is primarily related to the interpreted “possible” zones (of low or intermediate confidence of occurrence), for the most part located in the neighbouring Laxemar subarea and throughout the regional scale model volume. High rock stresses do not appear to be a major concern for the Simpevarp subarea. The current stress model indicates two stress domains, one with lower stresses in the Simpevarp subarea, east of deformation zone ZSMNE012A, compared with the area west thereof (including the Laxemar subarea) which shows comparatively higher stress levels. The magnitude of the maximum principal 5 stress (σ1) at 500 m in the Simpevarp subarea is estimated at 10–22 MPa. This situation, supported by numerical stress modelling, is attributed to unloading of a wedge-formed rock volume underneath the Simpevarp peninsula and Hålö and Ävrö islands, as delineated by the intersecting deformation zones. Quantification of mechanical properties of the naturally fractured rock mass and rock associated with interpreted deformation zones is supported by new laboratory data on intact rock samples, underpinned by empirical and theoretical relationships. The analysis of the thermal conductivity has developed considerably since Simpevarp 1.1. Our current understanding is that the thermal conductivity in the Simpevarp subarea is generally low. In terms of interpreted mean values for the identified lithological domains, the thermal conductivity varies within a relatively narrow interval (2.6–2.8 W/(m·K)). A methodology for upscaling of thermal conductivity data from core scale has also been developed.