RD&D-Programme 2004 - SKB

Figure 1-7. Basic layout of the deep repository.
The KBS-3 method has been under development since the early 1970s. The method was first
described in a report in 1983 as a basis for the decision to commission the most recently built
nuclear power reactors /1-3/. It has since served as a basis for SKB’s programmes for research
and development, at the same time as other methods have been studied in general terms.
In its basic configuration, the deep repository consists of a descent tunnel, shaft, central area
and a number of deposition tunnels, see Figure 1-7. In each deposition tunnel there are a number
of deposition holes. The location of the deposition tunnels, as well as the spacing between
the deposition holes, is determined above all by the consideration that the temperature on the
canister surface may not exceed 100°C. After the canisters have been emplaced in the deposition
holes, surrounded by impervious bentonite clay, the tunnel is backfilled with a mixture
of bentonite clay and crushed rock. Other chambers are also backfilled when all fuel has been
deposited.
An alternative layout of the KBS-3 repository, which has been a part of the picture since the
early 1990s, is horizontal deposition. In this case the canisters are emplaced in long horizontal
holes instead of short vertical holes, see Figure 1-8. The volume of extracted rock and backfill
in the deep repository would then be greatly reduced, since deposition tunnels are not needed.
Development of rock drilling technology has now come so far that this layout is an interesting
alternative to vertical deposition. Development of horizontal deposition, KBS-3H, will therefore
be conducted in parallel with the work on vertical deposition, KBS-3V, for the next few years.
Siting
The work of finding a suitable site for the repository goes on. In 2002, site investigations were
commenced in the municipalities of Östhammar and Oskarshamn. The selected sites are situated
near the Forsmark and Oskarshamn nuclear power plants. The initial phase of the site investigations
will last around two years and will include ground surveys and drilling of exploratory
holes down to a depth of one kilometre. The results from the initial phase will then serve as a
basis for preliminary safety evaluations, which can result in the investigations on a site being
interrupted prematurely if the site is not judged to have potential for meeting the requirements.
RD&D-Programme 2004 27