Kristina Skagius

Performance assessment of the geosphere barrier of a deep geological repository for spent fuel: The use of interaction matrices for identification, structuring and ranking of features, events and processes

This paper summarises a study where the basic device in the Rock Engineering Systems (RES) approach, the interaction matrix, was used to identify, structure and rank features, events, and processes (FEPs) describing barrier performance and radionuclide behaviour in the far-field of a deep geological repository for spent fuel. The study has shown that it is feasible to use an interaction matrix both for the structuring of the process system (PS) and for visualisation of the PS. The developed documentation system increases the transparency of the system description and makes it possible to trace back the judgements made during the construction of the matrix. This will facilitate review work and future revisions as well as consistent treatment of different issues in the system. This study is a first step in the application of a systematic method based on interaction matrices to establish a structured PS. The next step would be to develop the PS for the remaining parts of the repository system to the same level as has been done for the far-field system.

Porosities of and diffusivities in crystalline rock and fissure coating materials

The diffusion of non-sorbing species in different rock materials and fissure coating materials have been studied. The results show that the effective diffusivity of iodide in granites with fissure coating materials is of the same magnitude or higher as the effective diffusivity for iodide in granites without fissure coating material. Also the porosities of the granites with fissure coating material were higher. The effective diffusivity for iodide in rock materials without fissure coating material was determined to be from 1 x 10/sup -14/ m/sup 2//s to about 7 x 10/sup -13/ m/sup 2//s. To simulate the stress that exists in the bedrock at large depths diffusion experiments with iodide in rock materials under mechanical stress, and electrical resistivity measurements in salt-water-saturated rock cores under stress have been started. Electrical resistivity measurements is an indirect method to determine the diffusivity. Results from some initial measurements show that the effective diffusivity is reduced to about 40% of the value for unstressed samples at pressures of 230-280 bar. This is the expected stress at repository depths. 4 references, 3 figures, 1 table.

Devising scenarios for future repository evolution: A rigorous methodology

The Swedish Nuclear Power Inspectorate is developing a new methodology for the construction of scenarios for radiological consequence analysis as part of its SITE-94 performance assessment project. SITE-94 involves the incorporation of site specific data from the Aespoe site into a performance assessment (PA) of a hypothetical high-level waste repository. This paper describes a systems analysis approach that has been developed based on the concept of organizing all the events and processes which need to be taken account of in PA into a process system and a much smaller residual group which are used to generate scenarios. The methodology used for developing scenarios, producing calculation cases and addressing the various types of uncertainty involved in PA consequence analysis is described.

Chemical Transport in Fractured Rock

Transport of dissolved species in fractured rock has become an area of special interest in recent years when deep lying crystalline rocks have become potential sites for repositories for nuclear waste. In Sweden, research was started in 1977 to investigate the flow and transport in low permeability crystalline rocks such as granites and gneisses.

Diffusivities in crystalline rock materials

The diffusion of non-sorbing species in different crystalline rocks and fissure coating materials has been studied. The results show that the effective diffusivity of iodide, Uranine and Cr-EDTA in rock materials with fissure coating material is of the same magnitude or higher than in granites and gneisses. The results also show that it is not possible to assign one value to the diffusivity of a rock from a given area. The variations in properties are too large. The estimated effective diffusivity of iodide in rocks without fissure coating material was found to be in the range 1 x 10/sup -14/ m/sup 2//s to 70 x 10/sup -14/ m/sup 2//s. To simulate the stress that exists in the bedrock at large depths, diffusion experiments with iodide and electrical resistivity measurements in rock materials under mechanical stress have been performed. It was found that the diffusivity in rock samples at 300 - 350 bars, stress was reduced to 20 - 70% of the value in samples under atmospheric pressure.

Site Descriptive Modeling as a Part of Site Characterization in Sweden: Concluding the Surface Based Investigations

The Swedish Nuclear Fuel and Waste Management Co., SKB, is currently finalizing its surface based site investigations for the final repository for spent nuclear fuel in the municipalities of Osthammar (the Forsmark area) and Oskarshamn (the Simpevar/Laxemar area). The investigation data are assessed into a Site Descriptive Model, constituting a synthesis of geology, rock mechanics, thermal properties, hydrogeology, hydrogeochemistry, transport properties and a surface system description. Site data constitute a wide range of different measurement results. These data both need to be checked for consistency and to be interpreted into a format more amenable for three-dimensional modeling. The three-dimensional modeling (i.e. estimating the distribution of parameter values in space) is made in a sequence where the geometrical framework is taken from the geological models and in turn used by the rock mechanics, thermal and hydrogeological modeling. These disciplines in turn are partly interrelated, and also provide feedback to the geological modeling, especially if the geological description appears unreasonable when assessed together with the other data. Procedures for assessing the uncertainties and the confidence in the modeling have been developed during the course of the site modeling. These assessments also provide key input to the completion of the site investigation program.Copyright