RD&D-Programme 2004 - SKB

Two safety reports will therefore be produced, one for each application. In Figure 2 and hereinafter,
the reports are called SR-Can and SR-Site. The focus of these reports and the planning of
the work of producing them has been discussed with the authorities on a number of consultation
occasions. The intention is that SR-Can should be based on site data from the ongoing initial site
investigations, while SR-Site should be based on data from the complete site investigations.
The main purpose of SR-Can is to assess the safety of a KBS-3 repository at the sites now
being investigated, given canisters according to the application for the encapsulation plant.
Another purpose is to provide feedback to further canister development, the design of the deep
repository, and to future safety assessments and SKB’s programme for research on issues of
importance for long-term safety.
A planning document for SR-Can was published by SKB in 2003. A preliminary methodology
for the assessment was also outlined there. In addition, the focus and planning of SR-Can has
been discussed with the authorities on various consultation occasions. Recently an interim
report from the work was published for the main purpose of presenting and demonstrating the
methodology used, including updates based on the viewpoints of the authorities from their
review of SR 97. The interim report will be subjected to thorough expert review arranged by
the regulatory authorities. SKB will take into account the findings of this review in completing
SR-Can and later SR-Site.
Accounts of the preliminary safety evaluations of the sites where the site investigations are
being conducted are also planned to be published during 2004 (see section A4.5). The main
purpose of these evaluations is to determine whether previous evaluations of the suitability of
the site with respect to the long-term safety of a deep repository hold up in the light of borehole
data, and to provide feedback to the continued investigation activities and the design of siteadapted
repository solutions.
The safety assessment SR-Site will be based on data from the complete site investigations.
Most of the methodology and the presentation structure for SR-Can will also be used in SR-Site.
Certain interim assessments may also be published as references for SR-Can, while most interim
assessments based on site data will need to be repeated with the more refined models of the sites
that are developed during the latter part of the site investigations. To the extent that viewpoints
from the regulatory review of SR-Can are available, they will be taken into account in the
design of SR-Site.
A2.3.4 Horizontal deposition, KBS-3H
In its basic version, KBS-3 entails that canisters are deposited in holes with a diameter of
1.8 metres bored vertically downward from tunnels. The reference design entails depositing
one canister in each hole, which then needs to be made about eight metres deep. Alternative
variants with several canisters in the same hole and/or deposition in horizontal holes or tunnels
have been studied over the years. Comparative analyses have resulted in a decision to retain the
reference design with vertical deposition.
Horizontal deposition is not judged to offer any advantages compared with the reference design
when one canister is deposited in each hole. However, an alternative is to make much longer
horizontal holes (on the order of 100–300 metres) so that many canisters can be deposited in
a row. A prerequisite is that a canister and its surrounding bentonite can be deposited as a unit
surrounded by a perforated steel casing. This variant has in previous contexts been called MLH
(Medium Long Holes), but is referred to hereinafter as KBS-3H (Horizontal).
A KBS-3H repository offers advantages from an environmental and cost point of view. The
reason is that the long holes fill the double function of deposition tunnels and deposition holes,
or to put it differently, the need for deposition tunnels is eliminated. This reduces both the total
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