Method and device for decontaminating radioactivity

A radioactivity absorbing layer comprising a water absorbing polymer layer possessing a decontaminating agent is disposed between a hygroscopic first layer and a non-hygroscopic second layer. Heat applied from the portion above the second layer is transferred to the water-absorbing polymer layer. The decontaminating agent previously absorbed to the water-absorbing polymer leaches out from the water-absorbing polymer and migrates to the material to be decontaminated through the hygroscopic first layer. Subsequently, the decontaminating liquid containing radioactivity is absorbed again to the polymer layer by cooling these layers. The amount of radioactive wastes generated can be decreased. (T.M.)