Some congressional Democrats raised security concerns Wednesday about a proposed shipment of 300 pounds of weapons-grade plutonium (search) from the United States to France for conversion into a mixed-oxide fuel.

The Energy Department plans to send the plutonium by truck from the Los Alamos National Laboratory (search) in New Mexico to the navy yard in Charleston, S.C., where it will be loaded on a ship bound for Cherbourg, France, as part of a U.S.-Russian nonproliferation program.

Rep. Jim Turner (search) of Texas, the ranking Democrat on the Homeland Security Committee, said in a letter to Energy Secretary Spencer Abraham that he was concerned about the security of the shipment, especially when it reaches France.

"It is clear that extraordinary security is planned for the shipment," Turner said in his letter.

But, he said, he wants greater assurances that security for the shipment in France would be of the same level as planned for in the United States. He also questioned whether there had been adequate "independent oversight and review" of the shipment plan by other agencies.

Rep. Ed Markey (search), D-Mass., also raised concerns about the shipments. Markey, a member of the Homeland Security Committee, questioned whether the Department of Homeland Security has reviewed the plan.

The Energy Department says the shipment has been meticulously planned with high levels of security incorporated.

Once the shipment arrives in Cherbourg, it is to go by land to a French reprocessing facility, where the plutonium can be turned into a less dangerous mixed oxide. Then it is to be returned to the United States.

The Energy Department plans to use that material in four fuel assemblies at Duke Energy's Catawba nuclear power plant (search) in South Carolina. The test assemblies are part of a U.S.-Russian program in which each country has pledged to dispose of 64 metric tons of excess plutonium.

The United States plans to dispose of its material by burning it in commercial nuclear reactors as mixed oxide. However, the initial shipments have to be sent to France because the United States has yet to build a mixed-oxide processing facility.

Details of the shipment, including timing, are classified, but it is expected to occur later this year. According to the Energy Department, the plutonium would be carried on two British vessels guarded by specially trained British troops and escorted by the U.S. Coast Guard (search) in U.S. waters.