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Reduced pressure EBW of copper canisters for SKB, Sweden

Case Study

Equipment at SKBs canister laboratory
Equipment at SKBs canister laboratory

SKB manage the nuclear waste produced at Sweden's nuclear power stations. Their work is concerned with the storage of waste and long term disposal. Disposal of high level waste (i.e. spent fuel rods) has been the subject of a development programme carried out with TWI since the early 1980s. The Swedish method of disposal uses a copper canister some 5m high, 1m diameter, 50mm thick into which a number of spent fuel rods are inserted. SKB asked TWI to investigate the best method of sealing the lid onto the canister. The life of the canister needs to be at least 100,000 years. 

A number of welding processes have been considered but work has concentrated on the use of TWI's Reduced Pressure gun operating at up to 100kW of beam power. Partially penetrating welds in copper can be made of up to 70mm depth. Extensive work has been carried out at TWI on the development of equipment and welding procedures. In 1988 SKB installed a TWI Reduced Pressure gun at the Canister Laboratory in Oskarshamn, Sweden. Following commissioning this machine has been used to further refine welding procedures and test canister encapsulation. Whilst the equipment has been operated at Oskarshamn, TWI have continued to provide advice on welding, metallurgy and structural integrity.