Radioactive Waste Barrels are used to store (or as buffer for) radioactive materials. They delete their contents at a rate of 1 mB per minute.
The player can check the storage status of Radioactive Waste Barrels by crouching and right-clicking it with an empty hand. Green radiation particles start to appear as a barrel fills up (these are just a rough visual indicator of a barrel's fill ratio, not actual radiations).
Radioactive Waste barrels cannot be moved by any means (pistons, cardboard box, etc.). Also because barrels containing any radioactive waste cannot be broken safely, the only way to safely move a non empty barrel is to transfer its contents to another barrel before breaking it. This can be done by connecting a Pressurized Tube to its top or bottom side in pull mode.
Even if Radioactive Waste Barrels are somewhat blast resistant, pressurized tubes carrying waste to them are not. As a rule of thumb, do not allow creepers wandering around a fission reactor or waste transformation or disposal units.