Russia is taking highly disputed claims that Ukraine plans to use a dirty bomb on its own soil to the UN security council
A dirty bomb is a conventional explosive device laced with another substance, for instance radioactive material, designed to contaminate the immediate surroundings of a blast area. In the case of a dirty bomb using nuclear material, no fission takes place (as would occur in the detonation of a nuclear weapon). Usually seen as a potential terrorist weapon, it would have limited utility in conventional warfare.
