Regional Basic Professional Training Course in Korea

❙ 1041 ❙
20. Waste Management
The repository has been envisaged to be located at the depth of a few hundred meters –
about one kilometer. In the selection of disposal depth, several factors must be taken into
account. It must be sufficient to mitigate the impacts of above ground activities and
natural phenomena and to render human intrusion into repository very unlikely. The
temperature, hydraulic pressure and rock stresses tend to increase with depth while the
hydraulic conductivity and groundwater flow rate decrease with depth. The geological
structure of the host formation is naturally of importance for locating the repository.
Though many geological formations can provide excellent containment capability, the
safety of disposal cannot rest solely on this natural barrier. There is a need for other
barriers particularly during the first hundreds – thousands of years when the activity and
heat generation of HLW is high, and accordingly the conditions in the host rock are
disturbed, as compared with natural conditions. This initial containment is provided with
a waste canister; spent fuel bundles are enclosed into a durable container that preserves its
integrity for a very long time in the repository conditions. For the manufacturing of waste
canisters, several materials have been considered: iron/steel, copper, titanium, ceramic
materials and their compositions.
Spent fuel canisters cannot be placed into hard host rock as such but they must enclosed
by plastic buffer material, such as bentonite, that can tolerate minor rock deformations
and movements. The buffer can also contribute favorably to the chemical and
hydrological conditions around the canisters. A buffer is not necessary when waste
canisters are placed in plastic host formations, such as rock salt or some clay types.
After the completion of disposal operations and an optional surveillance period, the
openings in the repository will be backfilled and sealed. The intention is to bring the host
rock back to its natural conditions, as far as practicable. Some rock types have self‐
sealing capability, while special backfilling materials must be utilized for the others.