PROCESS FOR THE DECONTAMINATION OF RADIOACTIVELY CONTAMINATED MATERIALS

Abstract

The present invention relates to a process for the decontamination of radioactively contaminated material comprising the steps of a) providing radioactively contaminated material in a decontamination bath (200), b) providing a reactor unit (107) comprising a first reactor chamber (102) connected to a second reactor chamber (103), c) electrolyzing water with a ph>7 in the first reactor chamber (102) and generating (H.sub.3O.sub.2).sub.n, d) generating nanobubbles in the electrolyzed water of the second reactor chamber (103), e) optionally repeating steps c) and d), f) applying pressure to the water which contains nanobubbles, g) transferring the pressurized water which contains nanobubbles to a decontamination bath (200) containing an α-ray generator and the radioactively contaminated materiel, h) charging the nanobubbles with the α-particles emitted by the α-ray generator, and i) bringing the charged nanobubbles in contact with the radioactively contaminated material in the decontamination bath (200).

Claims

1. Process for the decontamination of radioactively contaminated material comprising the steps of a) Providing radioactively contaminated material in a decontamination bath (200); b) Providing a reactor unit (107) comprising a first reactor chamber (102) connected to a second reactor chamber (103); c) Electrolyzing water with a ph>7 in the first reactor chamber (102) and generating (H.sub.3O.sub.2.sup.−).sub.n ; d) Generating nanobubbles in the electrolyzed water of the second reactor chamber (103); e) Optionally repeating steps c) and d); f) Applying pressure to the water which contains nanobubbles; g) Transferring the pressurized water which contains nanobubbles to a decontamination bath (200) containing an α-ray generator and the radioactively contaminated material; h) Charging the nanobubbles with α-particles emitted by the α-ray generator; and i) Bringing the charged nanobubbles in contact with the radioactively contaminated material in the decontamination bath (200).

2. Process according to claim 1, characterized in that the steps b-d and f-h are replaced as follows b) Providing a reactor unit (107) comprising a filter chamber (130) connected to a first reactor chamber (102); c) Ionising, standardising and hydrogenising water in the filter chamber (130); d) Electrolyzing water with a ph>7 in the first reactor chamber (102) and generating (H.sub.3O.sub.2.sup.−).sub.n; f) Applying pressure to the water which contains (H.sub.3O.sub.2.sup.−).sub.n; g) Transferring the pressurized water which contains (H.sub.3O.sub.2.sup.−).sub.n to a decontamination bath (200) containing an α-ray generator and the radioactively contaminated material; h) Generating nanobubbles in the decontamination bath (200) and charging the nanobubbles with α-particles emitted by the α-ray generator;

3. Process according to claim 1, wherein the radioactively contaminated material is water.

4. Process according to claim 3, wherein the water contains tritium.

5. Process according to claim 1, wherein the radioactively contaminated material is a solid material.

6. Process according to claim 5, wherein the solid material is an organic material.

7. Process according to claim 5, wherein the solid material is an inorganic material.

8. Process according to claim 5, wherein the solid material contains caesium-137.

9. Process according to claim 1, wherein the pressure applied in step f) is in the range from 1 hPa to 20 hPa.

10. Process according to claim 1, wherein the radioactively contaminated material is treated in the decontamination bath (200) for a period of 0.25 h to 1 h.

11. Process according to claim 1, wherein in the steps c) to e) the temperature of the water is increased from room temperature to 80° C.

12. Process according to claim 1, wherein additionally nanobubbles are generated in the decontamination bath (201) during the entire treatment of the radioactively contaminated material.

13. Radioactively decontaminated material obtainable by a process according to claim 1.

14. Radioactively decontaminated material according to claim 13 having a radioactivity below 200 Becquerel/kg.

15. Device for performing a process for the decontamination of radioactively contaminated materials according to claim 1 comprising i. a decontamination tank (201); ii. a reactor unit (107); iii. a neutralization installation (300); and iv. a pipe (212).

16. Device according to claim 15, wherein an immersion basket (203) is positioned in the decontamination tank (201).

17. Device according to claim 15, wherein the neutralization installation (300) is positioned in water.

18. Device according to claim 15, wherein the neutralization installation (300) comprises i. a liquid chamber (310); ii. a gas chamber (320); iii. a spiral chamber (330); and iv. a nozzle (340).

19. Device according to claim 18, wherein the liquid chamber (310) comprises a mesh (312) and a grid (314).

20. Device according to claim 19, wherein the mesh (312) and/or the grid (314) are coated with an α-ray generating oxide.

21. Device according to claim 18, wherein the gas chamber (320) comprises a grid (314) and a ceramic ball (322).

22. Device according to claim 18, wherein the spiral chamber (330) comprises a spiral (104), a ceramic ball (322) and an outlet port (332).

23. Device according to claim 21, wherein the ceramic ball (322) is coated with an α-ray generating oxide.

24. Device according to claim 18, wherein the nozzle (340) comprises a gas pipe (342).

25. Device according to claim 15, wherein the reactor unit (107) comprises i. a first reactor chamber (102) comprising an electrode (105); and ii. a second reactor chamber (103) comprising a spiral (104).

26. Device according to claim 15, wherein the reactor unit (107) comprises i. a filter chamber (130); and ii. a first reactor chamber (102) comprising an electrode (105).

27. Device according to claim 25, wherein the electrode (105) comprises a plurality of electrode rods (501) and a plurality of sheets (502).

28. Device according to claim 27, wherein the sheets (502) comprise openings (503).

29. Device according to claim 25, wherein the electrode (105) is a three-phase electrode longitudinally arranged in segments (512).

30. Device according to claim 25, wherein the electrode (105) is arranged in a housing (514) with openings (516).

31. Device according to claim 25, wherein the electrode (105) comprises at least 12 electrode rods (501).

32. Device according to claim 26, wherein the reactor unit (107) comprises a plurality of filter chambers (130) which are i. an ion exchange filter (130′); and/or ii. a stone filter (130″); and/or iii. an obsidian stone filter (130″′).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0121] FIG. 1a shows a schematic view of a system of reactor units for the use of generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n.

[0122] FIG. 1b shows a schematic view of a system of filter chambers and a first reactor chamber generating (H.sub.3O.sub.2.sup.−).sub.n.

[0123] FIG. 2a shows a schematic view of a decontamination bath for solid material.

[0124] FIG. 2b shows a schematic view of a decontamination bath for water.

[0125] FIG. 3a shows a schematic view of a neutralization installation.

[0126] FIG. 3b shows a schematic view of a liquid chamber as a part of a neutralization installation.

[0127] FIG. 3c shows a schematic view of a gas chamber as a part of a neutralization installation.

[0128] FIG. 3d shows a schematic view of a spiral chamber as a part of a neutralization installation.

[0129] FIG. 4a shows a schematic view of a cylindrical electrode with 12 electrode rods.

[0130] FIG. 4b shows a schematic view of a cylindrical electrode with seven electrode rods in a housing with openings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0131] The present invention is explained in more detail with the following description without being meant as unduly limiting its scope to specific embodiments.

[0132] The inventive process is described based on the system of reactor units generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n 100 displayed in FIG. 1a. Water, e.g. filtered tap water is pumped into the system of reactor units generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n 100 with an input pump 101. The exerting pressure in the system of reactor units generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n 100 is controlled by a pressure valve 109.

[0133] The system of reactor units generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n 100 comprises reactor units 107 of a first reactor chamber 102 and a second reactor chamber 103 each. In FIG. 1a, four reactor units 107 are displayed, whereas in a preferred embodiment, six or seven reactor units 107 are used. Thus, ca. 40% more nanobubbles can be created as with less or more reactor units 107.

[0134] The first reactor chamber 102 is used to exchange oxygen with the water and create bubbles in it, thus transforming the water into (H.sub.3O.sub.2.sup.−).sub.n. Then, in the second reactor chamber 103 nanobubbles are created.

[0135] The first reactor chamber 102 typically consists of a stainless-steel cylinder with a length of 260 mm and a diameter of 55 mm, i.e. with a volume of ca. 617.76 cm.sup.3. In another embodiment, it has a much bigger volume, e.g. 30 m.sup.3. It contains an electrode 105, which is displayed e.g. in FIG. 4a and described in a subsequent section.

[0136] In a preferred embodiment, the electrode 105 in the first reactor chamber 102 is a three-phase electrode. Thereby, a three-phase current can be applied, e.g. with an average voltage of 200 V and an electric current of 220 A. The parameters of the three-phase current depend on the water quality used and can be adjusted by a person skilled in the art by means of some simple preliminary tests. The first nanobubbles are observed after passing the first reactor chamber 102. The flow of the water is indicated by arrows.

[0137] The second reactor chamber 103 consists of a stainless-steel cylinder with a length of 120 mm and a diameter of 19 mm, i.e. with a volume of ca. 339.6 cm.sup.3. It contains a spiral 104 which is in a preferred embodiment crafted from a rectangular metal sheet with a size of 120.Math.18 mm.sup.2. The metal can be stainless steel or aluminium.

[0138] In the second reactor chambers 103, nanobubbles are created. By repeating the electrolysis in the first reactor chambers 102 and the creation of nanobubbles in the second reactor chambers 103, at the end of the process, i.e after the water has passed through all reactor units 107, a stream of highly concentrated nanobubbles of (H.sub.3O.sub.2.sup.−).sub.n referred to as nano-(H.sub.3O.sub.2.sup.−).sub.n 210 in water having aggregates is created.

[0139] In a preferred embodiment, the nanobubbles are exposed to α-radiation. Thereby, the α-particles themselves can be stabilised by strong dipolar water molecules promoting nanobubble formation. Positively charged helium atoms are likely to form stable He.sub.2.sup.2+ molecules with a bonding order of one by combination with a helium atom. This can be shown by standard quantum mechanical calculations using the method of linear combination of atomic orbitals. Driven by the two positive charges, the molecules have the strong tendency to attract two further electrons from the environment.

[0140] Upon this event, dissociation into two separate helium atoms may occur which either stabilize the created nanobubbles or will contribute to the formation of further nanobubbles upon diffusion. However, the He.sub.2.sup.2+ molecules are able to transform again to helium upon interaction of the α-particle. Further, the noble gas radon which is formed during the thorium decay cascade can be emitted in the surrounding water and act as an α-ray generator in nanobubbles.

[0141] An alternative device for the generation of (H.sub.3O.sub.2.sup.−).sub.n is displayed in FIG. 1b with a system of filter chambers and a first reactor chamber generating (H.sub.3O.sub.2.sup.−).sub.n. The generation of (H.sub.3O.sub.2.sup.−).sub.n begins with pumping water into a reactor unit 107 by an input pump 101. First, it is transferred to an ion exchange filter 130′ which ionises the water. Thus, ionised water 142 is produced which is transferred to a stone filter 130″ where water clusters are broken down. Thereby, ionised and standardised water 144 is produced which is transferred to an obsidian stone filter 130′″ where its active hydrogen contents are increased. Thus, ionised, standardised and hydrogenated water 146 is produced which is transferred to a first reactor chamber 102. There, it is electrolyzed by an electrode 105.

[0142] The ion exchange filter 130′ can contain an ion exchange resin or an ion exchange polymer that acts as a medium for ion exchange. The exchanged ions can be cations or anions.

[0143] The stone filter 130″ can be made of barley stone, granite or any other fine-pored mineral stone.

[0144] The decontamination of solid material and water is conducted using specific embodiments of a decontamination bath 200. For solid material, it is a decontamination bath for solid material 200′ as displayed in FIG. 2a. For water, it is a decontamination bath for water 200″ as displayed in FIG. 2b.

[0145] In both embodiments, the decontamination bath 200 comprises a decontamination tank 201 which in a preferred embodiment consists of a stainless-steel container with an open top. In a preferred embodiment it is of rectangular shape with a size of e.g. 150.Math.200.Math.100 mm.sup.3 and a volume of 30 l.

[0146] For the decontamination, nano-(H.sub.3O.sub.2.sup.−).sub.n 210 are filled into the decontamination tank 201, where they are charged with α-particles. In a preferred embodiment, the nanobubbles are refreshed with additional stirring devices.

[0147] For the decontamination of solid material, the contaminated solid material is immersed in the decontamination bath for solid material 200′ in an immersion basket 203. In a preferred embodiment, the solid material to be decontaminated is left in the decontamination tank 201 for at least 15 minutes and maximum 30 minutes. A circulation pump 205 which is positioned in the decontamination tank 201 pumps the process fluid into a liquid chamber 310. In a preferred embodiment, the circulation pump 205 is a standard cascade pump with a leverage of 20 m.

[0148] The liquid chamber 310 is preferably an aluminum-brass amalgamated cylinder with a length of 200 mm and a diameter of 25 mm. In a preferred embodiment, it is filled with a mesh 312 as displayed in FIG. 3b which can be a roll of an aluminum mesh coated with thorium. In another preferred embodiment, the liquid chamber 310 contains ceramic balls 322. Preferably, the ceramic balls 322 have a diameter of 5 mm and are coated with thorium with a coating thickness in the range of 0.1-0.5 mm. The thorium coating is fixed on the ceramic balls 322, by a thermal process which takes 20-30 minutes.

[0149] The ceramic balls 322 are preferably spherical. Despite that, their geometry is not bound to be spherical. Alternatively, ceramic balls 322 of any other geometry suitable to be coated with thorium can be used, e.g. cubes, tubes, granules or flakes. In a preferred embodiment, the liquid chamber 310 is filled with about 750 ceramic balls 322 which are held in the chamber by grids 314 sealing the entry and the exit side. In a preferred embodiment, these grids 314 are coated with an α-particle emitting material, e.g. thorium. In another preferred embodiment, the liquid chamber is filled with thorium oxide granules.

[0150] The radioactivity of the α-rays is in the range of 1-100 MBq/kg, preferably 10-80 MBq/kg. A preferred example of the radioactivity is 17 MBq/kg. The energy of the emitted α-radiation is preferably in the range of 4-10 MeV. The exposure time of the nano-(H.sub.3O.sub.2.sup.−).sub.n 210 to the α-radiation is in the range of 15 minutes to 1 hour, preferably 15-45 min.

[0151] Simultaneously, a compressor 207 presses gas, e.g. air, helium, hydrogen or CO.sub.2 through a gas chamber 320. The gas type varies depending on the liquid radioactively contaminated material 220 and other features of the respective decontamination process. In a preferred embodiment, this gas chamber 320 is filled with ceramic balls 322 as displayed in FIG. 3c.

[0152] Thereupon, both streams from the liquid chamber 310 and the gas chamber 320 are mixed in a nozzle 340 and from there pressed into a spiral chamber 330 by the circulation pump 205. In a preferred embodiment, the nozzle 340 exhibits a gas pipe 342 adjacent to the gas chamber 320 enabling a targeted transfer of the gas from the gas chamber 320 to the nozzle 340.

[0153] In a preferred embodiment, it comprises three end-openings as displayed in FIG. 3a. The openings cross sections correspond to the adjacent chambers and are in a preferred embodiment of circular shape to enable a smooth flow. In a preferred embodiment, the opening towards the liquid chamber 310 has a diameter of 25 mm, of 15 mm towards the gas chamber and of 10 mm towards the spiral chamber. The reduction of the size of the flow cross sectional areas along the flow direction leads to an increase of the pressure in the neutralization installation 300, thus enabling a high process efficiency.

[0154] In a preferred embodiment, the spiral chamber 330 is a stainless-steel cylinder with a length of 150 mm and a diameter of 15 mm containing another aluminium spiral 104 with a length of 150 mm and a diameter of 13 mm. In a preferred embodiment, outlet ports 332 are positioned at the outer wall of the spiral chamber 330. Thus, nanobubbles can get emitted to the decontamination tank 201 continuously. Preferably, additional ceramic balls 322 are positioned in the spiral chamber 330 adjacent to the spiral 104. The spiral 104 refreshes the nanobubbles and the ceramic balls 322 refresh the load with α-particles and stabilize the decontamination degree of the output of the spiral chamber 330. In a preferred embodiment, multiple spiral chambers 330 are connected in a row one behind the other, e.g. up to 18 times. Thus, the decontamination degree is enhanced.

[0155] In a preferred embodiment, the liquid chamber 310, the gas chamber 320, the spiral chamber 330 and the nozzle 340 form a neutralization installation 300 as displayed in FIG. 3a. The water processed in the neutralization installation 300 is withdrawn via a pipe 212. It can be led directly into the decontamination tank 201 or led into another decontamination tank 201 of another decontamination bath 200. Thereby, it is possible to combine e.g. a decontamination bath for solid material 200′ with a decontamination bath for water 200″ with a single neutralization installation, a single compressor 207 and a single circulation pump 205. Thus, the installation costs can be reduced as well as the construction space.

[0156] Opposing to the decontamination bath for solid material 200′, the circulation pump 205 in the decontamination bath for water 200″ is positioned outside the decontamination tank 201. Depending on the requirements of water throughput of the liquid chamber 310 installed in the decontamination bath for water 200″, it can be of smaller size compared to that of the decontamination bath for solid materials 200′. Accordingly, the gas chamber 320 can comprise less ceramic balls 322 and the nozzle 340 can be of smaller size.

[0157] The liquid radioactively contaminated material 220, e.g. tritiated water or solutions of solid contaminated ground material solvated in water is filled into the decontamination tank 201 together with the nano-(H.sub.3O.sub.2.sup.−).sub.n 210. The ratio of the two liquids depends on the contamination degree of the liquid radioactively contaminated material 220. A higher decontamination degree requires more nano-(H.sub.3O.sub.2.sup.−).sub.n 210 and vice versa.

[0158] The circulation of the mixed liquids through the neutralization installation 300 is repeated until the radioactivity in the decontamination tank 201 reaches radiologically uncritical levels, e.g. a radioactivity below 200 Becquerel/kg.

[0159] In FIG. 4a a preferred embodiment of the electrode 105 is displayed. It is a three-phase electrode with a total length of 215 mm composed of a plurality of electrode rods 401. To enable a three-phase current, the number of electrode rods 401 has to be a multiple of 3, e.g. 12, 15, 18 or 21. Preferably, the electrode rods 401 have a diameter of 5 mm and consist of titanium or iron. If the resulting nano-(H.sub.3O.sub.2.sup.−).sub.n 210 is not intended for human consumption, the electrode rods 401 can also consist of stainless steel, which is not allowed to use for the production of drinking liquids as it emits harmful chrome. In a preferred embodiment, the electrode rods 401 comprise a platin amalgamated surface to prevent corrosion.

[0160] Preferably, the electrode rods 401 pierce through vertically positioned sheets 402, e.g. made from a plastic like PTFE. In a preferred embodiment, the electrode 105 comprises six sheets 402, resulting in a segmenting of the electrode 105 into seven segments 412. The segmentation is displayed in FIG. 4b. Preferably, the sheets 402 sealing tight with the wall of the housing 414, except for lateral openings 403 in each sheet 402 at one side opposite to the adjacent segment 412. Preferably, the housing 414 of the electrode 105 comprises openings 416 at the entry and the exit side to enable a continuous flow and thus, a continuous process. Preferably, the water is rising gradually up through the electrode 105. The lateral openings 403 in the sheets 402 induce a spiral flow of the water which flow direction is indicated in FIG. 1a with arrows in the first reactor chamber 102.

[0161] Preferably, the maximum power applied to the electrode rods 401 is 145,000±2,000 W. This value depends on the water quality used and can be adjusted in the above ranges by a person skilled in the art by means of some simple preliminary tests.

[0162] The experiment described in the following was carried out conducting the process and using the device of the present invention as described above. Radioactively contaminated bark from a poplar tree collected at 35 km distance to the Fukushima reactor (samples A, B and C) was washed in a decontamination tank 201 with nano-(H.sub.3O.sub.2.sup.−).sub.n 210 and with normal tap water (control sample A). The amount of iod-131 and the caesium isotopes caesium-134 and caesium-137 was measured before and after applying the decontamination process (before washing/after washing). The measurement method for nuclide measurement was carried out with gamma ray spectrometry using a germanium semiconductor detector. The results are displayed in the following table.

TABLE-US-00001 TABLE 1 Radioactivity of iod-131 and of the caesium isotopes caesium- 134 and caesium-137 in the bark samples A, B and C after treatment with nano-(H.sub.3O.sub.2.sup.−).sub.n and with tap water Radioactivity [Becquerel/kg] Sample I-131 Cs-134 Cs-137 Cs A before washing no result 188 1,110 1,298 after washing no result 13.1 76.5 89.4 B before washing no result 241 1,380 1,621 after washing no result 16.4 105 121.4 C before washing no result 145 1,017 1,162 after washing no result 11.9 82.7 94.6 control before washing no result 188 1,110 1,298 sample A after washing no result 154 765 819 (tap water)

[0163] The bark of the samples A, B and C show that the radioactivity is reduced to less than 200 Becquerel/kg or even less. Thus, it can be reused as a raw material for compost and soil conditioner.

REFERENCE LIST

[0164] 100 System of reactor units generating nanobubbles in (H.sub.3O.sub.2.sup.−).sub.n

[0165] 101 Input pump

[0166] 102 First reactor chamber

[0167] 103 Second reactor chamber

[0168] 104 Spiral

[0169] 105 Electrode

[0170] 107 Reactor unit

[0171] 109 Pressure valve

[0172] 120 System of filter chambers and a first reactor chamber generating (H.sub.3O.sub.2.sup.−).sub.n

[0173] 130 Filter chamber

[0174] 130′ Ion exchange filter

[0175] 130″ Stone filter

[0176] 130″′ Obsidian stone filter

[0177] 142 Ionised water

[0178] 144 Ionised and standardised water

[0179] 146 Ionised, standardised and hydrogenated water

[0180] 200 Decontamination bath

[0181] 200′ Decontamination bath for solid material

[0182] 200″ Decontamination bath for water

[0183] 201 Decontamination tank

[0184] 203 Immersion basket

[0185] 205 Circulation pump

[0186] 207 Compressor

[0187] 210 nano-(H.sub.3O.sub.2.sup.−).sub.n

[0188] 212 Pipe

[0189] 220 Liquid radioactively contaminated material

[0190] 300 Neutralization installation

[0191] 310 Liquid chamber

[0192] 312 Mesh

[0193] 314 Grid

[0194] 320 Gas chamber

[0195] 322 Ceramic ball

[0196] 330 Spiral chamber

[0197] 332 Outlet port

[0198] 340 Nozzle

[0199] 342 Gas pipe

[0200] 401 Electrode rod

[0201] 402 Sheet

[0202] 403 Opening

[0203] 412 Segment

[0204] 414 Housing

[0205] 416 Opening