RD&D-Programme 2004 - SKB

Conclusions in RD&D 2001 and its review
No description of rock support methods was presented in RD&D 2001. Mention was made of
SKB’s cooperation with Posiva, which is aimed at investigating and testing low-pH cementitious
materials.
Newfound knowledge since RD&D 2001
Formulations for bolt anchoring grouts have been developed within the framework of SKB’s
ongoing research programme for development and qualification of cementitious grouts that
produce leachate with a pH lower than 11. Silica fume and cement have been used and ground
together by different methods. The grouts have not yet been tested in the laboratory or under
realistic conditions in the field, and they have not been checked against requirements for
shrinkage and corrosion protection. The chances of developing structural concrete are deemed
to be good, but further studies and development are needed to obtain shotcrete with a low pH
and good adhesion.
In October 2003, SKB held an international workshop in Stockholm on the topic of qualification
of low-pH cements for use in geological final repositories. Participants from Belgium, Finland,
France, Japan, Spain, Sweden, Switzerland and the UK presented study results and plans for
the future. The participants also discussed and compared their views on low-pH cementitious
materials with respect to technology and long-term safety. The workshop provided a good
overall picture of the European research front in the field.
Requirements on the lifetime of different underground repository parts have been preliminary
determined via design premises for the deep repository’s underground part /10-7/. With a view
towards construction, deposition and backfilling, the lifetime of deposition tunnels has been set
at about five years. Underground accesses, operating caverns and transport tunnels have a much
longer lifetime. Their lifetime has been set at about 100 years, which is judged to be conservative
while at the same time permitting utilization of references regarding lifetime that have been
agreed on for facility construction in Sweden.
Supervisory procedures currently applied to SKB’s underground facilities (Clab, SFR, Äspö
HRL) should also be applicable to the deep repository, since similar design solutions and
materials will be used.
Programme
In cooperation with Posiva and Numo, studies are being conducted to investigate and test
whether low-pH cementitious materials in the form of bolt anchoring grouts and shotcrete
can be used for rock support.
SKB is participating in an integrated project within the EU’s Sixth Framework Programme
for research, technological development and demonstration (Engineering Studies and
Demonstrations of Repository Designs, Esdred) /10-8/ which includes development of
low-pH concrete that can be used as shotcrete for rock support.
10.2 Buffer
The buffer material being considered is swelling bentonite clay.
10.2.1 Requirements and premises
The buffer’s most important safety function is to retard transport between canister and rock. For
this reason it should have such low hydraulic conductivity that any transport of corrodants and
radionuclides will take place solely by diffusion. The buffer should also filter colloidal particles.
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