In this investigation the swelling pressure of confined samples of a real waste form, consisting of bitumen containing washing water concentrate, was measured. The theoretically reachable swelling pressure was estimated as high as ∼ 273 bar (27 MPa).

A first simple experimental set-up was a sample of bituminized radwaste embedded in a cylinder of sintered bronze with a piezo-resistive pressure transducer. This was put into a leaching medium. A maximum pressure of 2 bar (0.2 MPa) was measured. The leaching rates of these confined samples were similar to those of unconfined ones.

The second set-up was a sample of bituminized radwaste embedded in a cylinder of stainless steel, also equipped with a pressure transducer. The open bottom of the cylinder was closed with a disc of porous cement with water/cement ratio of 1.3. In two similar experiments with this set-up the swelling pressure reached in one case a value of 9 bar = 0.9 MPa and in the second improved one about 15 bar = 1.5 MPa.