Compositions – Radioactive compositions
Patent
1987-01-28
1989-05-09
Locker, Howard J.
Compositions
Radioactive compositions
134 1, 134 3, 134 2211, 134 2216, 134 24, 134 27, 134 28, 204 15, 204130, 204140, 2041415, 252 793, 252626, 252631, 252632, 423 2, 423 4, 423 18, 423 20, G21F 916, G21F 908, C09K 1308, B08B 900
Patent
active
048287598
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns an agent for decontaminating contaminated metallic or cement-containing substances. The invention also concerns, however, a process for the production of this decontamination agent by using boric acid, which is contained in the primary cycles of pressure water reactors. The invention furthermore concerns processes for using the decontamination agent. Although the decontamination agent in accordance with the invention is not restricted to the use of radioactively contaminated materials, the primary emphasis in the following description will be laid on this application.
2. Description of the Prior Art
In the past, the contaminated surface layers of reactor cooling conduits were frequently removed by means of aqueous mineral acid solutions. One such decontamination solution, with 20% nitric acid and 3% hydrofluoric acid, is cited, for example, in "Kernenergie" 11th year, 1968, page 285. Since, because of the aggressive nature of such mineral acid solutions, the removal process can only be controlled with great difficulty, there exists the danger that the pure metal below the contaminated surface layer will be corroded, so that weak points may arise, which may lead to the formation of leaks--which must in all cases be avoided. Of all the decontamination processes later developed in order to remove such or similar defects, the best known one must be the so-called "AP-Citrox" process ("Kernenergie", 11th year, 1968, page 285), in which the contaminated surface is first treated with an oxidizing alkaline permanganate solution to prepare for dissolution, and is then treated with a reducing, aqueous solution of dibasic ammonium citrate.
In U.S. Pat. No. 3,873,362, a similar two-stage decontamination process is described, in which, during the first stage, hydrogen peroxide is preferably used for oxidation, and, during the reducing, second process stage, aqueous solutions of mixtures of mineral acids (sulfuric acid and/or nitric acid) and complex-forming substances, such as oxalic acid, citronellic acid, or formic acid, are employed.
In accordance with another known decontamination process taught in German Pat. No. DE-PS 27 14 245, the contaminated metallic surface is treated with a cerous solution containing at least one cerium-IV-salt and a water-bearing solvent. A further decontamination process is described in European Patent Application, publication No. 00 73 366, in which an aqueous solution of formic acid and/or acetic acid is used as a decontamination agent, and, as a reducing agent, formaldehyde and/or acetaldehyde is used. In this process, it is particularly advantageous that a relatively slight need for chemicals exists, and, during the removal of the used decontamination solution, a quantity of precipitated radio-active substances corresponding approximately to the volume of the surface layers removed is used.
In the wet chemical decontamination processes which have been briefly described above, the basic concept is connected with the fact that the activity in the contaminated surface layer decreases with mass, as the surface layer itself is dissolved by the decontamination solution. The penetration depth of active material into the surface layer can be determined or measured before decontamination.
Decontamination tests on various metallic reactor components have only one conflict with the statement above, that the amount of residual activity is solely a function of the thickness of the surface layer removed. For various decontamination solutions, there are provided various decontamination factors with the same gravimetrically determined abrasion of layers. Research with a scanning electron microscope has shown that solid layers or islands of solids have formed on the decontaminated metal surfaces, in which active material is concentrated, and which are as considered as undesirable by-products of the specific abrasive reactions. Such variations are particularly observed in substances which contain silicon or aluminum, a
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"Dekontamination eines Reaktor-Kuhlwasserkreislaufs am Beispiel des Forschungsreaktors WWR-S in Rossendorf", H. Unger and D. Westphal, Kernenergie, pp. 285-290, Dec. 11, 1968.
Locker Howard J.
Speckman Thomas W.
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