RD&D-Programme 2004 - SKB

5 Canister – fabrication
The purpose of the canister in the deep repository is to isolate the spent nuclear fuel from the
surrounding environment. As long as the canister is intact, no radionuclides can escape from it.
To achieve isolation, the canister must:
• Be intact at deposition.
• Be resistant to the chemical environment expected in the deep repository.
• Withstand the mechanical loads expected in the repository.
Furthermore, it should be designed to provide high safety during encapsulation, transport and
deposition.
SKB’s reference canister consists of an outer corrosion barrier (shell) of copper and a pressurebearing
insert of nodular iron, see Figure 5-1. The canister holds either twelve BWR assemblies
or four PWR assemblies. It has a diameter of just over one metre and a length of nearly five
metres. The total weight, including fuel, is about 25 tonnes for a BWR canister and about
27 tonnes for a PWR canister.
The copper in the shell contains approximately 50 ppm phosphorus to increase the material’s
creep ductility. The pressure-bearing insert is made of nodular (spheroidal graphite) iron. The
spacing between the fuel channels is five centimetres and the minimum distance from the fuel
to the outside of the insert is about five centimetres, see Figure 5-2.
An important milestone has been reached in the development of the encapsulation technology
with the fabrication and sealing of a full-scale canister according to the quality plan.
1,050 mm
4,835 mm
50 mm copper
Estimated weight (kg):
Copper canister 7,400
Insert 13,600
Fuel assemblies (BWR) 3,600
Total 24,600
Figure 5-1. Copper canister with cast iron insert for BWR fuel.
RD&D-Programme 2004 45