Nuclear waste is the waste generated through nuclear power reactor. It is very harmful because it contains radioactive wastes composed of radioactive compounds like beta and gamma radiation, and actinides that emit alpha particles, such as uranium-234, neptunium-237, plutonium-238 and americium-241.
Radioactive compounds are very harmful because they take several years to decompose naturally. Exposure to such wastes causes mutations resulting in destructive effect on health and environment.