Final disposal

The Final Disposal Canister

Disposal canisters are massive metal casks. Their interior is made of nodular graphite cast iron, and the exterior is made of copper. With the spent fuel from the four nuclear power plants in operation and the fifth one under construction, some 2800 canisters will be needed for the final disposal.

Construction materials, structure, production methods and sealing technology of the final disposal canister have all been thoroughly examined so as to achieve a mechanically and chemically resistant container that can remain leak-tight deep inside the bedrock for at least 100,000 years. The capsule tightness is ensured by setting high quality standards for the manufacture and extensive inspections.

Copper Canister

The outer part of the final disposal canister is 5 cm thick and made of copper. It will protect the insert and the fuel assemblies from the corrosive effect of groundwater. Extensive experimental and theoretical studies of the outer casing corrosion, or erosion to the extent that leak-tightness would be lost, takes even in unfavorable conditions for hundreds of thousands of years.

Reserves of natural copper show that copper can last hundreds of thousands of years inside the bedrock without corroding. Therefore, copper has been chosen to the material of the disposal canisters outer cover. A further piece of evidence is a chisel, made of natural copper and found in Suomussalmi in Finland, that had resisted the above ground conditions and remained in good shape for thousands of years.

Cast Iron Insert

The interior of the final disposal canister is made of cast iron and is strong enough to resist the mechanical stress that the canister inside the bedrock is subjected to. The canister has been perfected to endure even extreme conditions, such as earthquakes, or the pressure inflicted by a continental glacier.

Cast iron has been selected because it is tenacious and strong and thus an ideal material for the interior of the canister. Cast iron is also easier to cast than many other materials, such as steel.

Three Different Canisters

There are three different fuel assembly types in the Finnish nuclear power plants: one in plants Loviisa 1 and 2, another in plants Olkiluoto 1 and 2, and yet another type in Olkiluoto 3, the plant currently under construction. Each fuel assembly size has its own canister design. All canister designs are 1.05 m wide, but their length varies according to the particular fuel assembly type in question.

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