Deposition holes

Posiva has opted for the so-called KBS-3V method for final disposal, which has been developed together with the SKB, Swedish Nuclear Fuel and Waste Management Company. It involves a final disposal principle, originally developed in Sweden, based on the multi-barrier principle. The acronym KBS comes from the Swedish compound word Kärnbränslesäkerhet, and the number 3 signifies the version. The letter V, for one, refers to the vertical placement of the canisters.

When only one final disposal canister is placed in a vertical deposition hole, there is not only bentonite but also rock between separating the canisters. The deposition hole is approximately 8 m deep and 1.75 m in diameter. The diameter of the canister is 1.05 m.

The Deposition Hole Boring Machine (DHBM) is one of the pieces of special equipment developed for final disposal. Requirements have been set for the holes to be drilled, the most important of which is to have a set of approved vertical axles. It is essential that the measured centre point of a deposition hole, which is 8 m deep, does not deviate at no depth by more than 25 mm from the vertical centre line between the starting point and the end point.

The test deposition holes used in the FISST test were drilled with a prototype machine named Sanna.