RD&D-Programme 2004 - SKB

A4.2 Site investigations
Site investigations are now being conducted in two municipalities, Oskarshamn and Östhammar.
The work is divided into two stages: initial and complete site investigation. Following the
initial stage, an evaluation is made which includes a preliminary safety evaluation where the
findings are cross-checked against the requirements made on the rock. If it turns out that any
site does not meet the requirements, the site investigation can be discontinued at this stage.
SKB’s planning assumption is, however, that the site investigations will be completed in both
municipalities.
A4.2.1 Forsmark
The site investigation in Forsmark pertains to an approximately 10 km 2 area extending southeast
from the nuclear power plant down towards Kallrigafjärden. The area largely coincides with the
extent of a so-called tectonic lens, which is a relatively well-preserved bedrock unit surrounded
by zones of highly deformed bedrock. The main arguments for the choice of the area were
that the bedrock is judged to be favourable, and that it has an advantageous location near the
industrial area, SFR and the harbour. The area is situated in a coastal environment with high
natural values, which imposes special requirements on both the site investigations and the
development of a deep disposal solution on the site.
The site investigation was initiated at the beginning of 2002. The organization and the activities
were built up and reached full scope during the first year. The current status of the investigation
can be summarized as follows:
• Characterization of the area’s geological and ecological conditions on the surface has largely
been completed.
• Five deep cored boreholes (1,000 metres) and a number of shallower percussion boreholes
(max. depth about 200 metres) have been completed for investigating the bedrock.
• A comprehensive, preliminary site description (version 1.1) has been presented.
• The consultation process for a possible deep repository in Forsmark has been commenced.
• An active information and communication programme has been established for ongoing
dialogue with nearby residents, the public, the municipality and other local stakeholders.
The data that have been analyzed so far have led to a focusing of the investigations to the
northwestern part of the area. It is not yet possible to make any reliable forecast of the final
results. Among other things, the preliminary safety evaluation, based on data after the initial
investigation stage, still remains to be done. At present, however, all signs indicate that the
site investigation in Forsmark will be completed, and that this will be done in keeping with the
timetable in Figure 10.
Before the site investigation was initiated, a number of site-specific geoscientific issues were
identified as being particularly important to clarify in order to judge the suitability of the site for
a deep repository. Table 1 summarizes the current status of these key issues in terms of how well
they are understood.
Besides issues that are specific for the site, there are numerous factors that are generally
important to clarify. These factors include the presence and frequency of dykes and fracture
zones, the water flow in these zones and the intervening bedrock, and hydrochemical and
thermal conditions. In the case of Forsmark, the general picture is that the bedrock near the
surface is characterized by unexpectedly high water flow in distinct structures. This contrasts
with conditions at greater depth, which are characterized by homogeneous, fracture-poor
bedrock with unexpectedly low water flow. As far as hydrochemical and thermal conditions
are concerned, the investigations have not revealed any surprises, which suggests favourable
conditions at repository depth.
RD&D-Programme 2004 387