A “dirty bomb” has never been used in conflict, and Tulane University political scientist Chris Fettweis doesn’t expect one to be used in the Russia-Ukraine war.

A dirty bomb is a mix of explosives, such as dynamite, with radioactive powder or pellets. When the explosives are set off, the blast carries radioactive material into the surrounding area.

Russia has accused Ukraine of planning such an attack. But those claims have been refuted by NATO, and U.S. officials have called them “transparently false.”