RD&D-Programme 2004 - SKB

The point of departure for the detailed account of the research programme is the KBS-3V
variant, i.e. vertical deposition holes bored from underground tunnels. But due to the fact that
the KBS-3H variant is attracting increasing attention, studies that are specific for horizontal
canisters surrounded by buffer and plugs in horizontal tunnels are also presented. The method
is described in greater detail in section 10.7. Research, development and evaluation of KBS-3H
are being carried out in close cooperation with Posiva of Finland. When it comes to research
with respect to long-term safety, many processes are of course common to the two variants; but
there are differences, especially with regard to the buffer. Various studies have been initiated,
and the state of knowledge, as well as the future programme, is presented in Chapter 17, for
example sections 17.2.7, 17.2.10 and 17.2.19. It can be expected that interest in the area will
increase and more studies will be started when work on the safety assessment for KBS-3H,
under the direction of Posiva, gets started in earnest.
13.2.1 Fuel
Dissolution of fuel, which occurs if it comes into contact with the groundwater via a breach in
the canister, is an important process to address in the safety assessment. Research on fuel dissolution
was prioritized in RD&D 2001, and some new results are presented in section 15.2.12,
along with the programme for continued studies. The area remains prioritized, at least until the
models for fuel dissolution have been examined in the SR-Can safety assessment.
13.2.2 Canister
For an intact canister in the repository, it is above all mechanical loads during glaciations and
earthquakes that must be considered. Material data are being collected and tests conducted
to enable the strength of the cast iron insert to be calculated. Newfound knowledge and the
continued programme are described in section 16.2.4. Copper corrosion continues to be an
important area in which different types of experiments are being conducted, sections 16.2.12
and 16.2.13.
For an intact canister, it is urgent to examine types and frequencies of defects that can occur
in the canister’s lid weld. Such information is being gathered from the trial weldings at the
Canister Laboratory, see section 16.1.2.
If it is assumed that the canister is initially damaged so that groundwater enters, the iron in
the insert can corrode. The scope and importance of this has been examined by means of
various kinds of experiments. Further iron corrosion experiments remain to be conducted,
see section 16.2.8.
13.2.3 Buffer
It is important to be able to predict the state of the buffer after full water saturation and complete
homogenization, and roughly how much time this takes. When water is absorbed from the
surrounding environment, the material is homogenized at the same time as the swelling pressure
builds up and thermal conductivity is altered. The course of events is being studied both in the
field and with models. The emphasis in the laboratory investigations has been on determining
the material parameters that are needed for the model calculations, see section 17.2.12.
A water-saturated buffer is simpler to describe, but there are still a number of processes that
need to be studied, not least in view of the long time spans that need to be considered. Processes
where additional research is needed include gas transport, section 17.2.6, colloid release and
erosion, section 17.2.19, and mechanical interaction between buffer and canister, section 17.2.9.
Some of the studies need to be broadened to take KBS-3H into consideration. An example is
the progressive deposition of finished canister-buffer parcels, alternating with plugs between the
parcels, creating a situation where erosion could occur, see section 17.2.19.
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