1. Field of the Invention
The invention relates to a method for solidifying radioactive residues from liquid waste of pressurized-water reactors which are also called concentrates and usually comprise boron in the form of borates.
2. Description of the Prior Art
It is known to solidify such concentrates by embedding them in binders by means of a mixing device. Worm dryers such as shown in German Published Prosecuted Application No. 22 40 119 are used, among others, as a mixing device. Bitumen is used particularly as the binder. However, the binder may also include plastics, for instance, polyethylene, as well as concrete or the like.
The residues to be embedded, which are usually concentrated by evaporation but are still liquid, are frequently accumulated over an extended period of time before they are present in an amount worthwhile for embedding. For this purpose, shielded containers are provided which, because of the radioactivity, are practically inaccessible. In this connection no disturbances must occur to the concentrate, for instance, through crystallization of boron compounds in the concentrate. Further difficulties in embedding the mentioned radioactive residues can result from the fact that the residues crystallize in being embedded. Extremely hard crystals can be produced in this connection so that, at a minimum, heavy abrasion results in the mixer used for the embedment with a greater danger of the hard crystalline solids blocking the mixing device. The water vapor and volatility of boron compounds can furthermore lead to incrustation at steam-carrying internals of the mixing apparatus under certain conditions. A further aggravating disadvantage of conventional embedment methods is that the end products have only low leaching resistance.