Euradwaste '08 - EU Bookshop - Europa

Figure 3.2.1 Schematic representation of Supercontainer concept (radial and axial cross-sections)
Requirements related to the backfill around the Supercontainer
In the O/N disposal concept for high level waste, the backfill component fulfills two functions:
1. The primary function of the backfill is to prevent a cave-in of the disposal drift, which might
damage the Supercontainer or distort the host rock surrounding the drift.
2. A secondary function of the backfill, applicable only to the disposal of spent fuel, is that the
backfill minimizes the existence of potential escape paths out of the Supercontainer for the
filler material present around the fuel assemblies.
Next to these functions, there are also constraints on the backfill component. Together, the functions
and the constraints determine the requirements for the backfill component. Two types of constraints
can be discerned:
1. constraints related to (long-term) safety:
• not disturb the corrosion-protective characteristics of the buffer (in Supercontainer);
• not act as a thermal isolator;
• not introduce organic materials that can give rise to migration-enhancing complexes;
• no excessive expansion or shrinkage or chemically attack the disposal drift wall;
2. constraints related to feasibility:
• exhibit the physical qualities that will allow it to be pumped or projected into the gap;
• achieve the needed industrial performance of the process;
• dust generation and water run-back should remain very limited;
• limit backfill strength, to keep the option of retrievability open as much as possible.
Backfill material
Because of its straightforward chemical compatibility with the disposal concept and the perceived
better opportunities for achieving the industrial performance, the grout injection technique is considered
by O/N to be the reference solution for backfilling disposal galleries. The development of a
grout fulfilling the requirements was a key process that was entrusted to BASF Construction
Chemical Belgium (formerly DEGUSSA). It resulted in a backfill grout, composed of:
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