Arbeitsbericht NAB 09-25

Numerical Modelling of the Thermo – Hydro – Mechanical Loading in a geological repository for HLW and SF

Der Bericht enthält keine Zusammenfassung.

Arbeitsbericht NAB 09-23

Glacial erosion: a review of its modelling

Résumé

Glaciers and ice sheets are important agents of erosion, transport and deposition and thus constitute an influential component in the evolution of the landscape which they cover. At the same time, glaciers and ice sheets respond dynamically to changes in boundary conditions, such as climatic variations and topographic adjustments. With the advent of numerical modelling techniques and recent advances in computer technology, modelling ice-sheet dynamics has become a powerful means to investigate the complex interactions between ice masses, the climate system and subglacial landforms in a quantitative way, in past as well as future environments.

Numerical models of ice flow have been applied to the existing ice sheets of Greenland and Antarctica, and those which covered the continents of the Northern Hemisphere during the Quaternary ice ages. Typical studies have concentrated on mechanisms and threshold of ice.sheet inception (e.g. Huybrechts 1994; DeConto & Pollard 2003a), ice-sheet form and extent during glacial–interglacial cycles (e.g. Marshall et al. 2000, 2002; Ritz et al. 2001; Charbit et al. 2002) and the response of the polar ice sheets to future climatic warming (e.g. Huybrechts & de Wolde 1999; Van de Wal et al. 2001). Related studies have considered ice sheets as sources of changes in surface loading for isostacy and gravity models (e.g. Le Meur & Huybrechts 2001; Tarasov & Peltier 2004) and changes in freshwater fluxes for ocean models (e.g. Schmittner et al. 2002; Fichefet et al. 2003). By accounting for interactions between thermal and flow regimes, ice-sheet models have also been used to investigate the potential for internally generated flow instability (e.g. Payne 1995; Payne & Dongelmans 1997; Marshall & Clarke 1997). In addition, models of the Greenland and Antarctic ice sheets are in use to assist with the dating and interpretation of ice cores (e.g. Greve 1997; Huybrechts et al. 2007).

In this review the emphasis is focused on the capability of glaciers and ice sheets to erode, transport and deposit substantial quantities of sediment. The discussion that follows concen.trates on models of ice flow that account for sediment erosion beneath glaciers and ice sheets. First, the main processes of glacial erosion and fundamental concepts of ice-sheet modelling are briefly introduced before various coupled ice-sheet/sediment models are presented and discussed.

Arbeitsbericht NAB 09-20

Borehole Gösgen KB5a: Mineralogy, Porosimetry and Pore Water Chemistry of the Effingen Member

Résumé

The Effingen Member (synonymous with Effinger Schichten) is one of the potential host rocks for the geological disposal for radioactive waste. First investigations of the Effingen Member date back to the Sediment Study performed by Nagra 25 years ago (Nagra 1988). More recently, the Effingen Member and surrounding lithologies have been investigated in more detail and applying most recent technologies in the EWS-borehole Oftringen (Waber 2008a).

Between October 2008 and January 2009 six cored (KB1, KB2, KB3, KB4, KB5 and KB5a) and one percussion-drilled (SB2) boreholes were drilled by KKG & Atel for various investiga.tions on the site of the nuclear power plant Gösgen. The geological and stratigraphic description of the rock material recovered from these boreholes is given by Albert et al. (2009). In addition, mineralogical, chemical and physical properties of the encountered limestones to calcareous marls and their pore water could be performed on the core material of borehole KB5a. At the Gösgen site the rocks of the Effingen Member (Oxfordian) occur between about 66 and 307 m depth, are overlain by the Geissberg and Olten Members and underlain by the Birmenstorf Member, all of Oxfordian age. The Effingen Member occurs thus at shallower depth below the surface and at somewhat greater thickness compared to Oftringen (420 – 642 m depth) located some 8 km southwest of the Gösgen site.

Pore-water from low-permeability rocks cannot be sampled by conventional groundwater tech.niques and has to be characterised indirectly based on originally saturated rock material. In case of the Gösgen borehole 2 samples could be conditioned on-site immediately after recovery in order to minimise artefacts induced by exposure to the atmosphere (e.g. evaporation, oxidation), and this constitutes a pre-requisite for a complete pore water characterisation. Further 10 samples were treated conventionally following about 4 months of storage under atmospheric conditions, which limited the pore water investigations for these samples. Indirect extraction methods deliver only partial information about the pore water composition and need to be supported by mineralogical and petrophysical data. By combining the results of different experimental and modelling techniques a pore-water composition might then be derived. The plausibility of the derived composition is assessed by comparing the spatial distribution of pore.water compositions with that of groundwater in over- and underlying aquifers and the palaeo.hydrogeological evolution of the area.

The present report describes the mineralogical, petrophysical and geochemical investigations performed on drillcore material obtained from borehole KB5a drilled at the Gösgen site. It should be noted that borehole KB5a was drilled only to about 156 m depth and samples for porewater investigations are restricted to the upper half of the Effingen Member rocks. Supporting data such as the geological and hydrogeological description are given in Albert et al. (2009) and Enachescu et al. (2010).

Arbeitsbericht NAB 09-15

Reference pore water for the Helvetic marls for the provisional safety analysis in the framework of sectoral plan – interim results
(SGT-ZE)

Résumé

Four variants of a Na-Cl reference pore water (Table 6-2) are suggested for the marl stack (Palfris Formation, Vitznau Mergel) at the Wellenberg siting region. Low-pH and high-pH variants gauge the uncertainty with respect to alkalinity and P_CO2. The redox conditions are reducing and modelled at pyrite equilibrium, but with negligible methane for the "base-case". A more reducing variant accounts for the observed high partial pressures of methane, and it is also modelled at pyrite equilibrium (Table 6-2). A "High-Na-Cl" variant with a high salinity (Table 6-3) is also modelled to cover the uncertainty in salinity arising from poorly constrained porosity data.

A Na-HCO₃-type pore water in analogy to the Na-HCO₃ fracture water of Nagra (1997b) was not included because a planned repository will be located well within the rock volume containing Na-Cl-type pore water. This region is expected to extend upwards as matrix rock into the zone with Na-HCO₃-type fracture water.

The Na-Cl reference pore water proposed here has a somewhat higher pH and lower P_CO2 compared to that of Nagra (1997b), but one of the different variants that bracket uncertainty is comparable. Redox conditions are modelled by mineral saturation constraints for all reference pore water compositions, or at a prescribed partial pressure of methane for the low-pε variant. All waters except the low-pε variant are sulphate-dominant compared to sulphide. The Na-Cl "base-case" reference pore water is similar somewhat more saline) to that derived by Baeyens and Bradbury (1994) used to derive a sorption data base.

A detailed historical and factual account of the relevant geochemical issues is provided and discussed in detail. Uncertainties and open issues are also addressed.

Arbeitsbericht NAB 09-14

Reference pore water for the Opalinus Clay and 'Brown Dogger' for the provisional safety-analysis in the framework of the sectoral plan – interim results (SGT-ZE)

Résumé

A single composition for a reference pore water for both the Opalinus Clay and "Brown Dogger" is proposed for all siting regions (Table 6-2). This reference pore water is very similar to that developed by Nagra (2002) for Benken. The uncertainty range (for Opalinus Clay) in the constraining P(CO2) is significantly reduced compared to 2002, resulting in a much reduced range in pH and alkalinity
(Table 6-4).

To account for the possibility that salinities as high as encountered at Mont Russelin (chlorinity of slightly more than modern sea water, 22 g/L), a high-salinity variant is also defined (Table 6-3).

Arbeitsbericht NAB 09-13

Reference pore water for the Effingen Member (Standortregion Südjura) for the provisional safety-analysis in the framework of the sectoral plan – interim results (SGT-ZE)

Résumé

Two reference pore water compositions are defined for the Effingen Member for the Jura-Südfuss area. One is a "low-salinity" (approximately sea water salinity) composition relevant for the upper and lower part of the Effingen Member towards the upper and lower bounding aquifers, and that is reasonably constrained by experimental data. A "high-salinity" pore water of twice sea water chlorinity is proposed as upper bound for the central part of the Effingen Member. Except for chlorinity and possibly Na concentrations, this composition is very poorly constrained, including sulphate and Ca concentrations, as well as pH and alkalinity. The compositions are listed in Table 7-8 and Table 8-1.

To further constrain the compositional uncertainty, variants with high sulphate concentration or with a higher partial pressure of CO2 (lower pH) are also provided, as well as a high-chloridehighsulphate combination (Table 9-1). Also, a lower-saline pore water is specified to reflect the uncertainty towards larger Cl-accessible porosity (Table 9-1). Full speciation details for these reference pore waters and variants are provided in Appendix 1-6.

The main uncertainties relate to the poorly constrained anion-accessible porosity (at least as low or lower than Opalinus Clay) and the Ca-sulphate-carbonate system (including pH, alkalinity and PCO2). This is largely rooted in the uncertainty to interpret laboratory data, and the inability to measure the composition of the exchangeable cations in borehole samples due to interference with mineral-water reactions during extraction procedures. Specifically, sulphate concentrations are poorly constrained and contradictory between experimental methods.

Arbeitsbericht NAB 09-07

Standortunabhängige Grundlagen
Anlagen und Betrieb SGT-ZE / SUG 2.3
Alternatives Ausbaukonzept (l"Liner concept") für BE/HAA-Lagerstollen

Résumé

Der Bericht enthält keine Zusammenfassung.