14.11.2014 09:54

Young maiden to replace a retiring lady

The Swedish SKB has acquired a state-of-the-art vessel for the sea transportation of spent nuclear fuel. M/S Sigrid will be transporting Sweden's spent nuclear fuel for at least the next 30 years. The vessel could be of use to other nuclear power operators as well.

M / S Sigrid transports spent nuclear fuel and radioactive waste from all nuclear power plants in Sweden to the temporary storage. Photo: SKB

In December 2013, a long-awaited arrival took place in Sweden. M/S Sigrid, the new transportation vessel of Sweden's nuclear waste management company SKB, gracefully entered the harbour on a sunny morning at the Ringhals nuclear power plant site. The vessel is nearly a hundred metres long, and it will transport spent nuclear fuel from all of Sweden's nuclear power plants to an interim storage facility in Oskarshamn.

“Sweden needed a new ship to take on the work. The old one was approaching the end of its useful life”, says project manager Jenny Holmström from SKB.

Holmström also points out that the advanced technology of the new vessel will save fuel and the environment compared to the old vessel.

Holmström has been involved in the Sigrid project from the start, nearly three years. The ship was built by the Dutch group Damen Shipyards at a Romanian shipyard. The work took two years.

“The project was a success. The ship meets our expectations, and the budget was kept. Delivery was slightly delayed, as we wanted the ship to be fully completed”, says Holmström.

The delay had no impact on the transportation operations in Sweden; SKB still had full use of the older vessel, M/S Sigyn. With Sigrid taking on the work, the thirty-year-old Sigyn will retire.

Hundred days a year at sea

After arriving in Sweden, M/S Sigrid has not been spending her days sunbathing at her home port in Oskarshamn. She was loaded with the first batches of spent nuclear fuel right at the beginning of 2014. According to Holmström, Sigrid now carries 80–100 transportation casks per year. The ship spends approximately hundred days of the year on duty in Swedish waters.

“We hope to be able to use Sigrid for the next 30 years. Until now, the ship has been exclusively used by SKB, but it could be used by other companies as well in the future”, says Holmström.

Road, rail or sea?

The method of transportation for the spent nuclear fuel from Loviisa to the final repository in Olkiluoto is yet to be established in Finland. The options are road, railway and sea transportation. Annual volumes to be transported and the size of transport casks have also not been determined.

“The current estimate is that the transportation method will be chosen in 2017 or 2018. At the moment, road and sea are the most likely alternatives, as railway transportation is a rather inflexible method and would require heavy investment”, says project engineer Jaana Palomäki from Posiva.

For sea transportation, Posiva is considering the option of leasing a suitable vessel from Sweden. A ship would accommodate a large number of transport casks at once, which means that only one or two loads per year would be required.

Road transportation would be a much more frequent operation. It would be carried out as supervised transportation.

Transport casks can withstand severe conditions

The fuel assemblies to be transferred from interim storage to Posiva's encapsulation plant are packed in impact-resistant transportation casks. The cask prevents any damage occurring to the fuel assemblies during the transfer and provides protection from radiation. Similar casks are also used when spent nuclear fuel is transported from the nuclear plant units to interim storage facilities.

The radiation protection provided by the transportation casks must not be compromised even in the worst conceivable accident.

The transportation of spent nuclear fuel is strictly regulated by national and international regulations and agreements. In Finland, a licence for each transport of spent nuclear fuel must be acquired from the Radiation and Nuclear Safety Authority.

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