Process for decontaminating radioactively contaminated metal or cement-containing materials

Abstract

Contaminated surface layers are decontaminated by treatment with an aqueous fluorine base-containing decontamination solution. The aqueous decontamination solution contains 0.05 to 50 Mol of decontamination agent per liter, and the decontamination agent preferably comprises at least one substance from the group: colon hexafluorosilicate acid, fluoroboric acid, and the salts of both of these. The decontamination solution produces the required high decontamination factors on metallic substances and brickworks as well. The used decontamination solution can, after regeneration, be recycled into the decontamination process.

Release of decontaminated material by dissolution of the surface layer of the decontaminated objects provides decontamination of objects having complicated and hard-to-measure geometries.

The decontamination agent (HBF₄ -acid) is advantageously produced from contaminated boric acid from pressurized water reactor wastes by reaction with fluoride or hydrofluoric acid. The HBF₄ -acid thus produced is, through distillation, separated from the contaminants and impurities.

Description

This is a (22) (21), which moves the reaction product from the reaction vessel (21) into a distillation device (25) of the known type. The rate of introduction of the two named components through the conduits (22) and (23) into the reaction container (21), and the rate of the removal of the reaction product from the reaction container, is so selected that enough time is allowed for completion of the stated reaction to the material transport. The sump, which remains behind in the distillation device (25), is removed and conditioned. For this purpose, the sump is first of all neutralized in a further vessel (26), for example, with calcium hydroxide. The neutralized sump material can be just simply dried again, and then removed as well. It can, however, also be reinforced with cement or bitumen, and then deposited. The heat energy necessary for distillation in the device (25) is advantageously removed in liquid or gaseous media. The distillation is advantageously carried out at low pressure, because the temperatures in the device (25) are then relatively low, and, at such temperatures, practically no pyrolysis takes place.

The HBF₄ -acid which is separated during the distillation is removed from the distillation device (25) through conduit; (26). This acid can be used as a completely regenerable decontamination agent, as is described in a Swiss patent application, number 2238/85, of the same applicant, or the acid can be sold to the chemical industry, where it can, for example, be used in galvanizing techniques.

The essential advantages of the present process are to be seen in the fact that the borofluoric acid, which is separated during distillation, does not reach the final storage area for radioactive material, but is sold, for example, to the chemical industry, and thus can be used again. The sump, because it has a smaller volume, can be removed, without entailing large costs. The knowledge that borofluoric acid HBF₄, in contrast to H₃ BO₃, is distillable, and can therefore be separated from the contaminants, such as, for example, Co-60 Cs-nucleides, forms the basis of the present invention. Furthermore, the borofluoric acid can be separated into fractions of various densities during distillation. The principal reactions, which are the basis of the present process, are as follows:

H₃ BO₃ +4 HF--HBF₄ +3 H₂ O+14.7 kcal.

In one practical case, 15.46 g of H₃ BO₃ was added to 20 g of HF within approximately 20 minutes.

EXAMPLE

10 m³ of boron-containing concentrate (16% H₃ BO₃) contains 1600 kg of boric acid (approximately 26'000 Mol). After evaporation, the fourfold mol-surplus of HF is mixed with the boric acid (104'000 Mol HF), that is, for example, 2457 liters of 70% HF, 1 liter at 12.00 Swiss francs (=Sfr. 29,500.00). The distillate yields approximately 26'00 Mol HBF₄, which comes out to 24,700.00 Swiss francs (1 liter=8 Mol-50%)=Sfr. 7.6). We obtain, according to the process used, 4500 kg of approximately 57% -HBF₄ -acid, or the corresponding dilution, according to the collected concentration of boric acid. The HBF₄ -acid obtained must contain no traces of activity (with the classification distillation), since it can be used as fully regenerable decontamination agent for components of DWR (pressurized water reactors) and SWR (boiling water reactors). The option for an inactive application (in galvanization technology, for example), exists with the execution of a multi-stage distillation process.

Claims

1. A process for decontaminating radioactively contaminated porous materials using a decontamination agent selected from the group consisting of fluoroboric acid; hexafluorosilicate acid; water soluble salts of fluoroboric acid; and mixtures thereof in aqueous solution, said decontamination agent having a concentration of about 0.05 to about 50 mol/liter in said solution, said process comprising contacting said radioactively contaminated porous materials to be decontaminated with said decontamination agent; and dissolving surface layers of said radioactively contaminated porous materials by said contacting with said decontamination agent; and separating said decontamination agent from radioactive contaminants and impurities by distillation.

2. A process in accordance with claim 1, wherein said porous materials are selected from the group consisting of metallic-containing materials, concrete-containing materials and brick-containing materials.

3. A process in accordance with claim 1, wherein said surface layers of said radioactively contaminated porous materials are dissolved by immersing said radioactively contaminated porous materials in said decontamination agent, and conditioning for removal a sump comprising said radioactive contaminants and impurities obtained after said separation from said decontamination agent by said distillation is transferred to a vessel for conditioning.

4. A process in accordance with claim 3, wherein said conditioning of said sump comprises neutralizing, drying and depositing with potassium hydroxide.

5. A process in accordance with claim 3, wherein said conditioning of said sump comprises neutralizing with potassium hydroxide, and then solidifying with at least one of cement and bitumen.

6. A process in accordance with claim 3, additionally comprising separating dissolved radioactively contaminated material from said decontamination agent during said dissolving of said surface layers; and recycling said separated decontamination agent to said decontamination process after said distillation.

7. A process in accordance with claim 3, wherein said radioactive contaminants and impurities are separated by chemical precipitation with hydroxides.

8. A process in accordance with claim 3, wherein solid secondary reaction products produced on the surfaces of said radioactively contaminated porous materials during said decontamination are mechanically removed from said surfaces of said porous materials.

9. A process in accordance with claim 3, additionally comprising separating said decontamination agent from said radioactive contaminants and impurities and testing said decontamination agent used for said dissolution of said surface layers of said radioactively contaminated porous materials after said distillation separating of said decontamination agent from said radioactive contaminants and impurities to determine the a composition of said decontamination agent.

10. A process in accordance with claim 7, additionally comprising electrochemically separating dissolved metals from said decontamination agent and removing said dissolved metals and the precipitate separated from said used decontamination agent when the radioactive contamination of said dissolved metals and said precipitate exceeds a predetermined value.

11. A process in accordance with claim 10, wherein said chemical precipitation with hydroxides comprises adding Ca²+ ions to said used decontamination agent in the form of Ca(OH)₂ to precipitate said radioactive contaminants and solid impurities, and separated precipitate is conditioned by solidifying with a cement to remove said radioactive contaminants and solid impurities from said used decontamination agent.

12. A process in accordance with claim 10, additionally comprising adding cations to said decontamination agent after said separation of said radioactive contaminants and solid impurities to convert said decontamination agent to a compound which is substantially insoluble in water.

13. A process in accordance with claim 3, wherein said used decontamination agent is distilled to drying and said sump product is pyrolyzed.

14. A process in accordance with claim 13, additionally comprising reacting said pyrolyzed sump product with hydrogen to produce metals and HF, and recycling said HF into a distillation device.

15. A process in accordance with claim 1 wherein said surface layers of said radioactively contaminated porous materials are dissolved by spraying said radioactively contaminated porous materials with said decontamination agent.

16. A process in accordance with claim 3 additionally comprising separating said decontamination agent from said radioactive contaminants and said impurities by electrochemical means.

17. A process in accordance with claim 8 wherein said mechanical removal comprises abrasively treating said surfaces with solid ice particles.

18. A process in accordance with claim 8 wherein said mechanical removal comprises abrasively treating said surfaces by brushing. 19. A process in accordance with claim 1 additionally comprising separating said decontamination agent from radioactive contaminants and impurities. 20. A process in accordance with claim 19 wherein said decontamination agent is separated from said radioactive contaminants and

impurities by distillation. 21. A process for decontaminating radioactively contaminated metal using a decontamination agent selected from the group consisting of fluoroboric acid; hexafluorosilicate acid; water soluble salts of fluoroboric acid; and mixtures thereof in aqueous solution, said decontamination agent having a concentration of about 0.05 to about 50 mol/liter in said solution, said process comprising contacting said radioactively contaminated metal to be decontaminated with said decontaminated agent; and dissolving surface layers of said radioactively contaminated metal by said contacting with said decontamination agent. 22. A process for decontaminating radioactively contaminated materials using a decontamination agent selected from the group consisting of fluoroboric acid; hexafluorosilicate acid; water soluble salts of fluoroboric acid; and mixtures thereof in aqueous solution, said decontamination agent having a concentration of about 0.05 to about 50 mol/liter in said solution, said process comprising contacting said radioactively contaminated materials to be decontaminated with said decontamination agent; and dissolving surface layers of said radioactively contaminated materials by said contacting with said decontamination agent.