A pilot study by Sweden's Studsvik AB shows that all of Norway's metallic uranium research reactor fuel could be processed using its oxidation process in less than two years. Several studies have already recommended chemical treatment of the fuel before it is disposed of in an underground repository.

In its hot cell laboratory, Studsvik has performed testing of treatment of metallic uranium fuel on a larger scale, with good results. The treatment method is applicable to the Norwegian used metallic fuel (Image: Studsvik)

Norway has about 17 tonnes of nuclear fuel from the Institute of Energy Technology's (IFE's) research activity at Kjeller and in Halden. About 10 tonnes of this fuel is unstable metallic uranium, which is extra challenging to manage.

Studsvik has completed a pilot study using its Small Scale Conversion process, which has previously only been used on a small sample of used nuclear fuel. The treatment method is called oxidation and involves heating the metallic uranium fuel with hot air in a furnace, converting it to stable uranium dioxide. In this project, Studsvik has built up the necessary equipment and performed a successful test of the method on a larger scale on more than 30 kg of nuclear fuel that corresponds to the Norwegian metallic fuel.

"It has been a great experience working with Norwegian Nuclear Decommissioning (NND) to develop the Studsvik Small Scale Conversion process," said Joakim Lundström, president of Studsvik's Fuel and Materials Technology business area. "Together we have been able to go from drawing board to proof-of-concept at a rapid pace, and we are convinced that this is a reliable and efficient long-term solution for handling of legacy spent metallic uranium fuels."

"This study shows a higher level of technological maturity than previously thought and reduces the uncertainties surrounding the implementation of the treatment," said NND Chief Technology Director Nils Bøhmer. "Thus, we have received confirmation that this treatment can be a good solution to stabilise the Norwegian fuel so that it becomes more suitable for final disposal.

"I am not surprised that it is feasible to treat larger amounts of fuel, but it is a positive surprise that the method has been proven to be so effective that all the Norwegian metallic fuel, about 10 tonnes, can be treated in two years. Since the time scale is shorter than expected, we have asked for an updated cost estimate to see whether it will be cheaper to implement."

The final decision on how the fuel will be prepared for disposal will be made by the Norwegian parliament. This decision will be based on studies carried out in accordance with the state's project model for large investments. In June 2020, NND completed a limited concept selection study for used fuel treatment, in which two methods for chemical treatment to stabilise the fuel were considered: reprocessing by Orano in France and oxidation by Studsvik. In the report, NND's staff make clear recommendations that the fuel should be chemically treated before disposal.

Research reactors

Norway's two research reactors - the nuclear fuel and materials testing reactor at Halden and the JEEP-II neutron scattering facility at Kjeller - were declared permanently shut down in June 2018 and April 2019, respectively. In addition to the research reactors, there are several other nuclear facilities that will be decommissioned and a wide range of nuclear waste that must be handled and disposed of in a safe way.

NND, established in 2018 as a government agency under the Ministry of Trade, Industry and Fisheries, is responsible for decommissioning the research reactors and other related nuclear infrastructure. NND is also responsible for the safe handling, storage and disposal of nuclear waste in Norway. The Norwegian state plans to transfer IFE's nuclear facilities and associated staff to NND, with a target date of the start of 2024. NND will at the same time become the licensee for the facilities.

In May this year, IFE signed a contract with Westinghouse subsidiary Springfields Fuels Limited for the transfer of 3 tonnes of unirradiated research reactor fuel to the UK for processing into new fuel for use in commercial nuclear power plants. The uranium fuel would otherwise have been treated as waste, stored and disposed of in Norway.

In January, Studsvik signed a contract with IFE for loading equipment, transport, handling equipment, examination and pre-treatment of used nuclear fuel from the JEEP I research reactor at Kjeller. Under an agreement, this fuel - comprising about 3 tonnes of metallically unstable uranium - will be transported to Sweden for processing before being returned to Norway for final disposal.

Researched and written by World Nuclear News