RD&D-Programme 2004 - SKB

ock volume that needs to be excavated and the tunnel volumes that need to be backfilled. The
technology for boring the long, large-diameter holes that would be needed has been improved
considerably in recent years. If such a design can be regarded as being equivalent to the
reference alternative, vertical deposition, in terms of overall technical feasibility and safety,
KBS-3H can therefore offer interesting optimization possibilities.
In view of this, SKB has decided to further develop horizontal deposition in holes with lengths
on the order of several hundred metres. A stepwise development programme has been devised,
and the work was commenced in 2002. The intention is to pursue the development work to the
point where KBS-3H can either be dismissed or substituted for the present-day reference design.
Much of the knowledge that is needed to evaluate KBS-3H can be taken directly from the
development work for vertical deposition. The repository’s surface facilities, descents and
central area are not affected at all, or only marginally, by how deposition is carried out. The
same applies to the deposition density and thereby the overall dimensions of the repository,
provided that the requirements on the rock are comparable. The encapsulation technology and
canister dimensions are the same as for the reference design. The same general knowledge
concerning the bedrock is applicable, and the site investigations being conducted now are
judged to provide the data needed concerning the rock on the site, regardless of which
deposition alternative (-3V or -3H) is chosen. The properties and function of the buffer
material are additional areas where existing R&D results are largely applicable to KBS-3H
as well.
There are, however, other issues where present-day knowledge is not directly applicable to
KBS-3H and where extensive development work is required, with large-scale testing and
demonstration. It will take time before a comprehensive evaluation of the method is possible.
Key issues identified by SKB regarding the technical feasibility of KBS-3H are:
• Boring of deposition holes (equipment and execution).
• Need and technology for sealing and rock stabilization in deposition holes.
• Fabrication of the deposition units.
• Deposition equipment and deposition sequence.
• Function of the buffer material (development during the initial water saturation phase after
deposition).
• Ability to meet the requirements on long-term safety.
• Possibility of retrieval.
SKB’s development programme is focusing on these issues, see Figure 5. A feasibility study and
the first of three main stages (basic design) were carried out in cooperation with Posiva during
2002 and 2003. The results of completed technical studies and practical trials have warranted
the more ambitious stage which is now in progress. Besides studies of technical key issues and
preparations for a safety assessment, it also includes full-scale demonstration trials at the Äspö
HRL. Two holes are planned to be bored and deposition equipment will be designed, built and
tested. The first goal is to demonstrate that the method is practically feasible. If so, a full-scale
performance test will be arranged, with preliminary start in early 2006. The safety assessment
will be carried out by Posiva, preliminarily in 2006.
If the plans illustrated in Figure 5 can be implemented according to schedule with clear
results, RD&D-Programme 2007 will be a suitable occasion for a summarizing status report
on KBS-3H. The technology development and demonstration phase will then be finished and
the safety assessment completed. What may be lacking, however, are complete data from the
full-scale trial that is planned to be under way at that time, but will be at a relatively early stage.
Furthermore, it can be assumed from experience that those parts of the development programme
that will have been completed by then will have raised questions that require additional work.
374 RD&D-Programme 2004