Patent Number: 045004498
Section: summary

BACKGROUND OF THE INVENTION 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. SUMMARY OF THE INVENTION It is an object of the invention to provide an improved method of conditioning liquid concentrates of boron-containing radioactive residues to be solidified by embedment in a binder such that storage and embedment can be carried cut in an optimum manner, optimum meaning, among other things, that the amount of residue relative to the amount of binder is maximized. With the foregoing and other objects in view there is provided in accordance with the invention a method for solidifying radioactive liquid concentrate residues from liquid wastes of pressurized-water reactors containing boron in the form of borates by embedding the residues in a binder by mixing in a mixing device, the improvement comprising prior to said embedding in a binder, adding sodium hydroxide to the waste concentrate to obtain a mole ratio of sodium to boron of about 0.25 or 0.7 with a respective corresponding pH value in the range of 7.3 to 8.0 or 9.8 to 10.2 and mixing the waste concentrate to which sodium hydroxide has been added with a binder to embed the waste concentrate in the binder. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a method for solidifying boron-containing radioactive residues, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.