RD&D-Programme 2004 - SKB

the long-term safety of the concept. The horizontal deposition drifts are planned to be up to
300 metres long and have a diameter of 1.85 metres, which is 10 centimetres more than the
deposition holes in KBS-3V. The deposition drifts must be straight and meet narrow dimensional
tolerances so that deposition will proceed smoothly. The feasibility study recommended
that rock excavation using the cluster technique be further studied. Equipment for boring of
the deposition drifts using this technique has been developed and tested, see section 10.1. The
copper canister and the buffer will be placed in a deposition container of steel and the whole
parcel, which weighs about 50 tonnes, will be emplaced in the horizontal deposition drifts.
A spacer block of bentonite clay is placed between the deposition containers.
Development of deposition technology and machinery for this is under way. According to the
plans, the remote-controlled deposition machine will utilize water cushions to reduce friction
during transport along the deposition drifts. Studies of the function of the bentonite showed
that about 60 percent of the surface area of the deposition containers should be perforated so
that the bentonite will swell out and seal the deposition drift. The function of the spacer blocks
in sealing and preventing erosion of the bentonite buffer has been studied in laboratory tests
on different scales. The tests show that there is a risk of erosion and piping if there is a large
hydraulic gradient, so studies of these matters continue, see section 17.2.19. A site at a depth of
220 metres in the Äspö HRL has been selected to demonstrate the concept on a full scale. The
preparations for demonstration began during the summer of 2003, when a niche was blasted out
and three cored boreholes were drilled to characterize the rock.
The safety evaluation of the proposed concept has been reviewed by external experts from
Enresa, Nagra and Numo. The conclusion of the review was that the concept is judged to be
technically feasible and to meet the requirements on long-term safety. KBS-3H is thereby an
alternative to the reference method.
Programme
The remaining points in the research, development and demonstration programme for KBS-3H
will mostly be carried out during the period 2005–2007 in cooperation with Posiva and within
the EU’s Sixth Framework Programme and the Esdred project /10-8/. The principal remaining
step is manufacture of the requisite equipment, demonstration of this equipment at the Äspö
HRL, performance of a safety assessment and evaluation.
The principal technical activities planned during the period 2004–2007 are:
• Boring of two horizontal deposition drifts in the Äspö HRL.
• Detailed design and manufacture of deposition equipment.
• Demonstration of deposition equipment in the Äspö HRL.
• Execution of feasibility study and basic design of equipment for retrieval.
A full-scale test may also be carried out at the Äspö HRL in order to verify the function of the
bentonite during the initial water saturation phase. A decision in this regard will be made during
2004. If the decision is positive, the field test will start during 2006.
A safety assessment for KBS-3H based on site data from Olkiluoto in Finland will be performed
by Posiva (section 14.1). This will be preceded by studies and research on critical questions,
modelling, preparation of a process report and analyses of radionuclide transport. Examples
of questions are swelling-out of the bentonite through the perforated deposition container
(section 17.2.7), pressure build-up as a consequence of corrosion of the deposition container
(section 17.2.10) and piping and erosion of the bentonite (section 17.2.19).
The research, development and demonstration programme will be concluded with an evaluation
of the concept and reporting of results in 2007.
128 RD&D-Programme 2004