RD&D-Programme 2004 - SKB

Studies of equipment will be conducted in stages to provide support for Layout D1 and
Layout D2 for the underground part of the deep repository. The studies will also provide the
necessary background material for the preparation of preliminary operational safety reports
with associated analyses.
What is currently being discussed and planned is:
• The scope of radiation protection during the deposition process, which directly influences
the size of the deposition machine.
• The deposition machine – a conceptual study is planned of a wheeled deposition machine
instead of the rail-bound machine currently used at the Äspö HRL. The study will give
answers regarding feasibility, requirements on roadway and whether sufficient accuracy
can be achieved for positioning.
• Handling and emplacement of buffer, which is linked to the choice of technology for
compaction of the buffer units and how they will be transported to the repository level.
The reference alternative for transport of the buffer units is that they will be transported
on the ramp to the repository level.
• Demonstration may be necessary to verify that the chosen method and equipment for
handling will work in the deep repository.
10.4 Backfilling and closure
The purpose of ongoing studies is to develop concepts for backfilling of deposition tunnels
and other rock caverns and closure of the deep repository.
10.4.1 Requirements and premises
The purpose of backfilling deposition tunnels and other rock caverns is that the barrier
functions of the rock will be retained. The backfill is therefore not a barrier in itself. The
following requirements are therefore made on the backfill:
• In order that the deposition tunnels should not constitute conductive pathways that affect
the water flux in the repository, the backfill, over the entire cross-section and length of the
tunnel, shall have a hydraulic conductivity that is comparable to that in the surrounding rock,
or is so low that the dominant water transport mechanism is diffusion.
• In order that the density of the buffer should be preserved, the backfill shall have a compressibility
that limits the upward expansion of the buffer so that the function of the buffer
is retained.
• The backfill shall be durable so that its functions are retained in the environment expected in
the deep repository.
• Technical and financial feasibility.
Furthermore, backfilled deposition tunnels must not have an adverse impact on the barriers in
the repository. Materials and backfilling technique shall be chosen so that they do not lead to an
unacceptable impact on the environment.
10.4.2 Materials and compaction technology
Conclusions in RD&D 2001 and its review
Different materials and methods for backfilling of tunnels, rock caverns and shafts in a deep
repository have been considered in SKB’s development work through the years, for example
bentonite and crushed rock, bentonite and quartz sand and crushed rock alone have been investigated.
SKB is developing and testing compaction technology and materials for backfilling.
122 RD&D-Programme 2004