COMPLETE DOCUMENT (1862 kb) - OECD Nuclear Energy Agency

The disposal geometry to be selected for a specific repository site must be compatible with the
different thermal requirements imposed by the specific medium. The thermal analysis performed
recommended a spacing between emplacement drifts of 50 to 100 m for clay, 35 m for granite and 23 m
for salt. The length of the waste emplacement drift will be limited to 500 m for practical reasons, with a
cross-section of about 5 m 2 and capacity for up to 87 disposal canisters. For adequate buffering, the
space between canisters has been fixed at 1 m for granite and salt options, and 2.5 m for a clay option.
Once the emplacement activities are finished, all open space inside the repository mine must
be backfilled and sealed. Different backfilling materials will be used (in-situ compacted reconstituted
clay for the clay option, in-situ compacted mixture of bentonite and sand for the granite option, and insitu
compacted crushed salt for the salt option). Filled regions will be isolated from the rest of the
emplacement area by means of dedicated seals. The repository area will be isolated by seals in the
access shafts.
A probabilistic performance assessment for a generic site in a granitic host rock formation has
been completed. It has permitted evaluation of the relative importance and performance of the various
components of the repository total system as well as a sensitivity analysis of the various parameters.
A normal evolution scenario, with appropriate performance ascribed to the designed
engineering barriers, has been considered as reference scenario. A hydrogeological regime based on
present-day conditions and a reference biosphere has been assumed.
Figure II.28 shows the mean dose rates obtained for the normal evolution scenario averaged
over 100 simulation runs. A peak dose of 2.36 µSv/year, well below the regulatory limit of
100 µSv/year, is reached 600 000 years after waste disposal, with 129 I responsible for 99% of it.
Figure II.28 Evolution of mean dose rates in the case of disposal
of 40 GWd/tHM UOX spent fuel
10 -6
Total
Mean dose rate (Sv/year)
10 -7
10 -8
10 -9
10 -10
10 -11
10 -12
I-129
10 -5 10 3 10 4 10 5 10 6
Se-79
Pd-107
Sn-126
Cl-36
Ra-226
Cs-135
Th-230
10 -13
Time (year)
221