RD&D-Programme 2004 - SKB

comprehensive and gives evidence of a good understanding of relationships between initial
properties and long-term processes, and that there is no reason to assume that a buffer with
acceptable properties cannot be found.
However, SKI points out that it is difficult on the basis of SKB’s account in the RD&Dprogramme
to make independent judgements of individual areas due to couplings and
repercussions on other areas.
17.1 Initial state of the buffer
17.1.1 Variables
In SR 97, the buffer was described by a set of variables, see Table 17-1.
The initial state, i.e. the value these variables were assumed to have at the time of deposition,
was described in the main report of SR 97, section 6.4 /17-1/. The research programme around
the initial state for the different variables in the buffer is described in the following.
Table 17-1. Variables for the buffer and the backfill.
Variable
Geometry
Pore geometry
Radiation intensity
Temperature
Montmorillonite
content
Water content
Gas contents
Hydrovariables
Swelling pressure
Montmorillonite
composition
Pore water
composition
Impurity levels
Definition
Geometric dimensions of buffer/backfill. A description of e.g. interfaces on the inside towards
the canister and on the outside towards the geosphere.
Pore geometry as a function of time and space in buffer and backfill. The porosity, i.e. the
fraction of the volume that is not occupied by solid material, is often given.
Intensity of α, β, γ and neutron radiation as a function of time and space in buffer and backfill.
Temperature as a function of time and space in buffer and backfill.
Montmorillonite content as a function of time and space in buffer and backfill.
Water content as a function of time and space in buffer and backfill.
Gas contents (including any radionuclides) as a function of time and space in buffer and backfill.
Flows and pressures for water and gas as a function of time and space in buffer and backfill.
Swelling pressure as a function of time and space in buffer and backfill.
Chemical composition of the montmorillonite (including any radionuclides) in time and space
in buffer and backfill. This variable also includes material sorbed to the montmorillonite surface.
Composition of the pore water (including any radionuclides and dissolved gases) in time
and space in buffer and backfill.
Levels of impurities in time and space in buffer and backfill. Impurities also include
other minerals than montmorillonite. In backfill, crushed rock is counted as an impurity.
17.1.2 Geometry
The geometry of the buffer is determined by the dimensions of the canister and the thickness
of the buffer material required to obtain the desired function. In SR 97 and RD&D 2001, the
dimensions of the canister were given and the dimensions of the buffer were set at 35 cm on
the sides of the canister, 50 cm underneath the canister and 150 cm above the canister. These
dimensions still apply to KBS-3V, while there are small differences for KBS-3H.
Conclusions in RD&D 2001 and its review
SKI points out that SKB must make the choice of an optimal buffer (properties and availability)
before a permit application is submitted. Kasam takes a positive view of SKB’s plans to conduct
studies of alternative buffer materials in order to get an alternative reference to bentonite with a
high montmorillonite content.
RD&D-Programme 2004 195