Greenpeace activists have chained themselves to the railings of a train station in northern France to protest against the shipment of fuel by a British company.
MOX fuel, a mixture of uranium oxide and plutonium, is due to be sent by rail to Cherbourg next week, before being shipped to Japan by Pacific Nuclear Transport Limited.
Around 10 activists are involved in the protest at Valognes.
Greenpeace say that the MOX fuel is produced at two factories in Belgium, including a subsidiary of French state-owned nuclear group, Cogema.
Greenpeace has often clashed with Cogema, which has a nuclear reprocessing plant in La Hague, near the port of Cherbourg.
Most of Japan's imported MOX fuel is transported from Europe by ship.
The shipments have triggered protests by environmentalists who say they are vulnerable to accident or attack by terrorists.