RD&D-Programme 2004 - SKB

A third type of seal is intended to prevent or hinder intrusion in the underground facility after it
has been backfilled and sealed. SKB judges that detailed technical solutions for this can wait.
Conclusions in RD&D 2001 and its review
SKB’s judgement in RD&D 2001 was that sufficient knowledge will exist regarding the design
and construction of temporary seals once planned experiments are completed. Temporary seals
in the form of plugs are included in the full-scale Backfill and Plug test and the Prototype
Repository experiment at the Äspö HRL.
Newfound knowledge since RD&D 2001
Temporary seals in the deposition tunnels can be designed in different ways. The type of plug
that has been installed in the Backfill and Plug test and the Prototype Repository experiment is
a reinforced plug anchored in a slot in the rock around the tunnel. Another type is a friction plug
which is held in place by the friction between the rock wall and the plug.
The design of the two reinforced plugs installed in the Prototype Repository differs somewhat
from the plug in the Backfill and Plug Test in that they lack a sealing ring of bentonite and have
been cast in self-compacting concrete certified by the supplier. Friction plugs have not yet been
tested in the Äspö HRL.
Programme
Establishing performance requirements, technical solutions and a fabrication method for plugs
is part of the development programme being conducted by SKB with regard to backfilling and
closure of the deep repository. In a completed feasibility study within the framework of this
programme, it was concluded that there is a need to conduct an inventory and evaluation of
possible concepts for seals, both with temporary and permanent function. The choice of concept
for seals is dependent on, among other things, which method is used for excavation of the rock
and which backfilling concept is used.
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/. A part of the project deals with
development and validation of technology for development of temporary seals made of
low-pH cementitious materials. For example, the programme includes application and
qualification of a temporary seal made of low-pH shotcrete.
A technical solution for sealing of horizontal deposition tunnels will be arrived at prior to the
demonstration of KBS-3H, with horizontal deposition of the canisters, that is planned at the
Äspö HRL in 2006. According to current plans, at least one of the deposition tunnels will be
sealed with a friction plug made of shotcrete based on low-pH cement. The KBS-3H method is
described in greater detail in section 10.7.
10.5 Sealing of investigation boreholes
10.5.1 Requirements and premises
Rock excavation and operation of the underground part of the deep repository facility will have
only a limited impact on the safety performance of the rock and the other barriers. Investigation
holes from the surface and from tunnels in the deep repository must therefore be cleaned and
sealed no later than at the closure of the deep repository.
124 RD&D-Programme 2004