Concerns that a calcium residue might be flammable prompted officials at Los Alamos National Laboratory to curtail plutonium operations and suspend waste shipments in early November, according to a federal report.

The lab suspended most waste generation and certification at its plutonium facility and halted all waste shipments after officials questioned the accuracy of documentation, particularly on how much calcium-and-salt residue remained in transuranic waste after processing, the Defense Nuclear Facilities Safety Board, an independent oversight panel, said in a Nov. 15 report that was publicly released Friday.

Calcium is used to help reduce oxidation in plutonium. Traces of the substance typically linger after processing, and if they are too high, they can ignite when exposed to open air, the report says.

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