Radioactive waste means radioactive material:
- in gaseous, liquid or solid form
- for which no further use is planned by the national authorities or by anyone whose decision-making power is recognised by the authorities
- that is regulated by a national regulatory authority.
There is no universally agreed categorisation scheme. However, the International Atomic Energy Agency (IAEA) has published Safety Standards on Classification of Radioactive Waste.
Generally, for practical and planning purposes, national authorities classify waste according to its radioactivity content and its half-life (the time taken for the radioactivity content to decrease by half).