Canisters with vitrified residues

Proof of freedom from contaminationDuring the "vitrification" process, the radioactive residues are fused with a special glass (borosilicate glass) at approx. 1,100° Celsius to bind it. The fusing is comparable to the colouring of glass bottles. In this process, the dye, for example iron in green wine bottles or cobalt in blue vases, forms a unit with the glass and cannot be removed from the glass even by crushing or heating.

The still liquid glass mass is filled into a stainless steel canister, and solidifies as it cools. The canister is then tightly closed with a welded-on stainless steel lid. The highly radioactive substances are thus firmly enclosed inside the canister.

The cylindrical canister has a diameter of 43 cm and a height of 134 cm. It can hold approx. 400 kilograms of glass mass, which on average contains the fission products from, for example, approx. three reprocessed standard pressurised water reactor fuel elements.

The external contamination-free condition of the entire surface of each canister is then determined by measurement. After it has been proven that there is no surface contamination, the canisters are transferred to special intermediate storage facilities of the reprocessing plants. During this intermediate storage both the heat generation and the radioactivity decrease over time.