PROCESS FOR THE DECONTAMINATION OF RADIOACTIVELY CONTAMINATED MATERIALS

Abstract

 The present invention relates to a process for the decontamination of radioactively contaminated materials and products comprising the steps of a) Providing radioactively contaminated materials and/or one or more products b) Creating nanobubbles in water in at least one first reactor c) transferring the nanobubles in water in a second reactor comprising a thorium source d) Applying pressure to the second reactor and e) transferring the pressurized water with nanobubbles to a decontamination tank containing the radioactively contaminated material and/or products. Treatment in the decontamination tank reduces the radioactivity of contaminated materials below 200 Becquerel / kg.

Description

[0001] The present invention relates to the weakening the energy of radioactive materials by immersing radioactive contaminants in a cleaning solution.

[0002] After the radioactive leakage due to the nuclear accident at Fukushima Daiichi Nuclear Power Plant following the Great East Japan Great Earthquake of March 2011, various industrial fields were seriously damaged.

[0003] One of the most imminent problems is the handling a large amount of radioactive contaminants generated during decontamination operations. Because of the high radiation dose, it is not general waste and thus left in the temporary storage place, and consequently even temporary storage cannot be secured at last. One of the most pressing objectives and challenges was therefore to develop a method that can effectively reduce radioactivity without creating highly contaminated disposals. Radioactive materials derived from the nuclear accident include I-131, Cs-134, Cs-137, Sr-90, Pu-239, etc

[0004] One of the radioactive materials generated in large amounts is wood from the forests surrounding Fukushima.

[0005] Immediately after the accident, specifically the bark of trees have been contaminated by huge amounts of radionuclides.

[0006] Many methods for reducing radioactive contamination have been proposed, most of which rely on the use of materials such as zeolites or plants to adsorb radionuclides, and just shielding in a certain container. In such processes, the absorbents become radioactive and should require subsequent disposal, usually by long-term burial. It is therefore highly desirable to find a way for radioactive decontamination by converting radioactive nuclids into stable elements without any radioactive activity.

[0007] Sugihara (Water 5, 69-85. 2013 and Int. J. Curr. Res. Aca.Rec. 2015; 3 (8): 196-207) suggested the use of "infoton" containing activated water put under high pressure in specifically designed activated pots to decontaminate radioactively contaminated soil from Fukushima and claimed to have reduced the radioactivity of the soil by up to 60%. The radioactivity could be reduced by treatment with activated water or with an energized substance exposed to activated water. The experiments were conducted with contaminated soil samples which were placed in a specially treated pot together with water. The pot was fabricated from pellets of acrylic-styrene which were energized by immersion in pressurized water and repeated detonation. Injection molding of the pellets yielded the pot.

[0008] The authors explained this phenomenon of reduced radioactivity as the effect of an extended particle on a nucleus as for example ¹³⁷Cesium (¹³⁷Cs). Bleecker D, Wilson L (1978) Stability of Gauss maps. Illinois J Math 22: 270-289; and Shima H, Ono S, Taira H. (2009) Quantum mechanics on a curved surface and its application to materials science. J Surf Sci Soc Jpn 30: 652-658 suggest that the potential around the nucleus and particle is of spherical shape with Gaussian curvature enabling a reaction within an extremely short time and very small space in the picosecond and picometer range respectively. Upon breakage of a hydrogen bond of a water molecule the proton and electron remain inside the water molecule instead of forming hydronium ions or hydroxyl ions. The energy associated with spin and momentum is retained and a weak terahertz radiation is emitted. This fragment carrying energy in a water molecule is called an infoton. The Infoton is an elementary particle with a stable existence and proton and electron being in a plasma state. This hypothetic particle is assumed to function as a long-wavelength electromagnetic wave. Its energy transfers to another substance in form of an electromagnetic wave. The authors explain the long wavelength synthesis of elements by reaction of ¹³⁷Cs with high energetic infotons whose energy corresponds for example to 1170 keV at 5% of light velocity, which is close to the photon energy from ¹³⁷Cs. With decreasing distance between ¹³⁷Cs and the infoton the potential curvature increases under reduction of the energy of the ¹³⁷Cs nucleus through emission of photons. Concurrently the infoton regains energy from ¹³⁷Cs causing it to climb the potential slope which facilitates the interaction with the nucleus and leads to the formation of stable elements.

[0009] Analytical investigations of infoton treated aqueous soil extracts showed that the radioactive materials were converted into Ba, La, and Ce. The detected levels of these elements were markedly different from those usually found in soil.

[0010] Sugihara (Sugihara et al. EC Agriculture 5.3 (2019): 134-138) described recently the change of instable radioactive elements to stable ones.

[0011] Nanobubbles have attracted much attention over the last years see for example (see J. Meegooda et al., Environmental Engineering Science, Vol. 35, 11, published online 5 Nov. 2018 and http://www1.lsbu.ac.uk/water/nanobubble.html.

[0012] Nanobubbles or ultrafine bubbles are defined as cavities of gases with diameter <200 nm in aqueous solutions Industrial application of nanobubbles has exponentially increased over the past two decades due to their reactivity and stability, compared with macro- and microbubbles. Due to the size, they have high specific surface areas and high stagnation times which increases mass transport efficiencies, physical absorptions, and chemical reactions at the gas-liquid interfaces. Moreover, these bubbles have long residence time in solutions and electrically charged surfaces. Due to the above, nanobubbles have many industrial applications such as manufacturing of functional materials, soil and sediment decontamination, pharmaceutical delivery, and disinfection of food products.

[0013] After generation, nanobubbles are found to exist in aqueous solutions for several weeks. It was reported that bubbles of radii 150-200 nm were in a solution for 2 weeks. Without being bound by theory, it is assumed that the electrically charged liquid-gas interface of nanobubbles create repulsive forces that prevent bubble coalescence and, hence, high bubble densities creating highly dissolved gas concentrations in water creating smaller concentration gradients between the interface and the bulk liquid. Moreover, the stability of bubbles increased by low rising velocity, which is negligible due to Brownian motion and low buoyancy forces. Other than these reasons, nanobubbles are considered to be stable by a mutual shielding against the diffusive outflow of gases, which can be achieved if bubbles are sufficiently close together or gathered into micrometer-sized clusters. It also appears that they can change the physico-chemical properties of water (see for example http://www1.lsbu.ac.uk/water/nanobubble.html., Ushikubo et al. Colloids and Surfaces A Physicochem. Eng. Aspects (2010), doi:10.1016/j.colsurfa.2010.03.005)

[0014] As of now, presence of stable nanobubbles has been experimentally confirmed, yet a clear theoretical basis has not been established to explain their long-term stability. Hence for effective and functional use of these bubbles, knowing their properties and behavior is quite important. Yet, nanobubble behavior is considered to be complex. Li et al described the use of water nanobubbles for groundwater remediation (Li et al. Int. J. Environ. Res. Public Health 2014, 11, 473-486; doi:10.3390/ijerph110100473).

[0015] The problem underlying the present invention was therefore to provide a novel process of decontaminating radioactively contaminated materials and/or products. These decontaminated materials/and or products could then be used by humans without the fear of being radioactively contaminated by these materials/and or products. It was a further specific object of the present invention to decontaminate organic materials from nature like soils, wood, cut grass (hay) etc for smoothing the effect of nuclear contamination by nuclear power plant accidents on nature.

[0016] This problem has been solved by a process for the decontamination of radioactively contaminated materials and products comprising the steps of

a) Providing radioactively contaminated materials and/or one or more products

b) Creating nanobubbles in water in at least one first reactor

c) Transferring the nanobubbles in water in a second reactor comprising an α-ray source

d) Applying pressure to the second reactor

e) Transferring the pressurized water with nanobubbles to a decontamination bath containing the radioactively contaminated material and/or products

[0017] The material and/or product to be contaminated is in one preferred embodiment a natural organic material, like wood, its bark, hay, organic components of soil any products comprising organic components like cotton, wool etc. In another preferred embodiment the material and/or product to be decontaminated is an inorganic material, like milled concrete, steel, plastic, inorganic components of any products comprising any inorganic components. After treatment the radiation dose of the material/product is considerably lower than the levels allowed for human use so they can be further processed or reused and brought in contact with humans.

[0018] The α-ray source is preferably a thorium containing compound. The thorium containing compound, especially preferred is thorium oxide, may be used as such or for example as a coating on three dimensional bodies, likes regular or irregular balls, cubes, tubes, granules, flakes etc. In another preferred embodiment, thorium oxide is packed into a column as 10 mm granules and passed through this column. The intensity dose of the α-rays is in the range of 1 MBq / kg to 100 MBq / kg, preferably 10 MBq/kg to 80 MBq/kg. A preferred example of the dose intensity is 17MBq / kg The time of exposure of the water with nanobubbles to the α-radiation is in the range of 15 minutes to 1 hour, preferably 15 min to 45 min. The energy of the emitted α rays is in the range of 4 MeV 10 MeV.

[0019] The first reactor is preferably at least one electrolytic cell for the generation of the nanobubbles when the water is passed through the cell. The reactor is typically a tank made of stainless steel and in a specific embodiment with a volume of 30 m³. It is preferred that a plurality of such interconnected cells are used., at least 2, most preferred 6 or 7 of these electrolytic cells. It was found that the optimum results can be obtained with 6 or 7 cells, where more than 40% more nanobubbles were created as with lesser or more cells. Hitherto, nanobubbles were frequently generated in solutions by creating cavities. Cavitation is caused by pressure reduction below the certain critical value. Based on the pressure reduction mechanism, cavitation mechanisms can be classified into four different types (Meegoda et al. vide supra)

• Hydrodynamic variation in the pressure of liquid flux due to system geometry
• Acoustic-acoustic cavitation produced by applying ultrasound to liquids
• Particle-passing high intensity light photons in liquids
• Optical-short-pulsed lasers focused into low absorption coefficient solutions

[0020] Nanobubbles are further hydrodynamically generated using the following methods

• Dissolve gases in liquids by compressing gas flows in liquids, then releasing those mixtures through nanosized nozzles to create nanobubbles.
• Inject low pressure gases into liquids to break gas into bubbles by focusing, fluid oscillation, or mechanical vibration.

[0021] Microbubbles generators have been described by Ushikubo et al (Physicochem. Eng. Aspects (2010), doi:10.1016/j.colsurfa.2010.03.005) and Takehiko Sato et al 2015 J. Phys.: Conf. Ser.656 012036.

[0022] Surprisingly, the present inventors found that via passing through a plurality, preferably 5 to 7 of electrolytic cells, nanobubbles could be generated as well. In an especially preferred embodiment 7 electrolytic cells were used. As already discussed before, ca 40% more nanobubbles were created than with using 3, 4 and 5 cells or 8, 9 and 10 cells.

[0023] It is also part of the present invention that the generation of the nanobubbles occurs in a process where temperature during passage of water through the plurality of electrolytic cells is increased gradually from room temperature in the electrolytic cell 1 to 90°C over 15 min. in the last electrolytic cell of the plurality of interconnected cells. It was observed, that it is advantageous to increase the temperature in the last electrolytic cell exponentially over this period and not gradually.

[0024] Further the maximum voltage applied to the electrodes is 145.000 +/- 2000 W. This value depnds 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.

[0025] As shown in figure 1, there are also two reactors ("boxes") in one electrolytic cell : the so-called A Box is for Oxygen exchange and to create bubbles in the process of electrolyzing water, and the so-called B Box then creates thereof nano-Bubbles

[0026] In the "A Box" starts the reaction, and in the B Box the nano-bubbles are created and submitted to alpha radiation from the thorium source.

[0027] Preferably the water in the electrolytic cell has a pH > 7, preferably below a pH of 10. It was found that stable bubbles were generated under pH values above 7, preferably 7,5 to 8,5. Increasing the pH increases the zeta potential of the nanobubbles. Moreover, this will increase hydrogen bonds around the bubbles and helps to increase the stability of the bubble as well. Nanobubbles tend to be smaller in size with increased pH values compared to neutral pH conditions. The nano-bubbles have a bubble particle size in the range of 5 nm -50 nm and a density of 3 vol% -15 vol% calculated on the amount of water.

[0028] Even though nanobubbles in high pH solutions showed highly negative zeta potential value at the time of generation, it rapidly reduced to values close to zeta potential values of nanobubbles produced with neutral solution pH Also, the results revealed, nanobubbles in acidic solutions were difficult to generate and those zeta potential values tend to be positive. This confirms the finding that the surface charge of nanobubbles is strongly related to the OH^- ion concentration.

[0029] The electrolytic cell contains a cylindrical electrode comprising a plurality of rod-shaped electrodes. The number of these rod-shaped electrode may vary between 12 and 21. The thorium source are ceramic balls coated with Thorium. Thorium nuclei are susceptible to alpha decay because the strong nuclear force cannot overcome the electromagnetic repulsion between their protons. The alpha decay of ²³²Th initiates the 4n decay chain which includes isotopes with a mass number divisible by 4.This chain of consecutive alpha and beta decays begins with the decay of the naturally occurring ²³²Th to ²²⁸Ra and terminates at ²⁰⁸Pb. The thorium cascade includes the following elements: actinium, bismuth, lead, polonium, radium, radon, thallium. All elements are present at least transiently in any natural thorium containing sample, whether metal, compound or mineral. The total energy release from ²³²Th to ²⁰⁸Pb including the energy lost to neutrinos is 42.6 MeV. The ²³²Th decay chain includes alpha (α) as well as beta- (β^-) decays. The α-decay is defined by the emission of an α-particle which has an atomic mass of 4 a.u. and consists of 4 neutrons and 4 protons which is consistent with the nucleus of a Helium atom and can also be expressed in the form ⁴He²⁺ a two times positively charged Helium atom. By emission of an α-particle the atomic mass of the decaying element is decreased by 4, namely 2 protons and 2 neutrons (2p2n) this yields a new isotope of an element having an order number reduced by 2 in the periodic system of the elements (PSE). On the other hand the β -decay is defined by the emission of an β-particle, which is a high energetic electron from the nucleus. In case of the β^--decay a neutron of the nucleus is transformed into a proton under release of an electron accompanied by an antineutrino. By the β^--decay the number of protons in the decaying nucleus is increased by one yielding therefore an isotope of a new element with an order number increased by one in the PSE having approximately the same mass of the nucleus before the decay. The first step in the ²³²Thorium cascade is the decay of 232Th90 (nucleus consists of 90 protons and 142 neutrons: 90p142n) to 228Ra88 (radon nucleus with 88 protons and 140 neutrons: 88p140n) under emission of 2p2n. In short: 232Th90 → 228Ra88 + 2n2p. This step is followed by two β^--decays to Actinium (228Ac89) and Thorium (228Th90). By consecutive α-decays isotopes of Radium (224Ra88), Radon (220Rn86), Polonium (216Po84) and finally lead (212Pb82) are formed whereby several β -decays are also occurring. By these numerous α-decays Helium nuclei are formed.

[0030] Without being bound by theory it is assumed that the thorium will contribute to the reactivity of very stable nanobubbles. The alpha particles which are radiated by Thorium are positively charged Helium nuclei. In water these nuclei have a typical diffusion wavelength of about 40 µm until they are thermalized. Due to the increase of the water flow rate by applying pressure the α-particles can overcome far larger distances before thermalization. On their way through the liquid they are able to capture electrons under formation of Helium atoms. Since Helium is a noble gas it is not likely to undergo chemical reactions and is a very stable monoatomic compound. The thermalized He²⁺-nucleus has a strong tendency to reach the uncharged stable He-state by the uptake of 2 electrons from the surroundings.

[0031] In their thermalized state they can get be trapped either as neutral atoms or positively charged particles under forming nanobubbles with surrounding water molecules. Such bubble formation is consistent with observations from Demangeat (Homeopathy. 2015 Apr;104(2):101-15. doi: 10.1016/j.homp.2015.02.001. Epub 2015 Mar 13) who showed that nanobubbles may be formed spontaneously from dissolved gas.

[0032] On the other hand the α-particles themselves can be stabilized by strong dipolar water molecules promoting nanobubble formation. Positively charged Helium atoms are likely to form stable He₂²⁺ molecules with a bonding order of one by combination with an 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 has the strong tendency to abstract two further electrons from the environment. Upon this event dissociation into two separate Helium atoms may occur which either stabilize the created nanobubble or will contribute to the formation of further bubbles upon diffusion. However the He₂²⁺ 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 α-source in nanobubbles.

[0033] The occurrence of α-particles as well as α-particle containing He₂²⁺ promotes the formation of reactive nanobubbles.

[0034] The pressure applied in step d) is in the range from 1 hPa to 20 hPa.

[0035] The material and or products are treated longer in the decontamination bath, it was found that the decontamination decreases.

[0036] The decontamination bath comprises further a nanobubble source so that additional nanobubbles are generated during the entire treatment of the materials and/or products in the contamination bath.

[0037] The present invention relates further to radioactively decontaminated material and/or products obtainable by a process as described above.

[0038] The invention relates further to an electrode for use in a process above having a cylindrical housing with openings. The electrode comprises at least 12 electrode rods arranged in the cylindrical housing, preferably 21 rods.

[0039] The invention is explained in more detail in the following section and figures without being meant as unduly limiting the scope of the present invention to specific embodiments.

Figure 1 shows a schematic view of a plurality of electrodes used for the generation of nanaobubbles

Figure 2 shows a schematic view of the reactor and decontamination tank

Figure 3a shows a cylindrical electrode in side view

Figure 3b shows a cylindrical electrode in top view with 12 rod shaped single electrodes

Example 1

[0040] Radioactively contaminated bark from a poplar tree collected at 35 km distance to the Fukushima reactor was washed in a tank with normal tap water (comparative example) and with water with nanobubbles obtained as specified in the present invention and the amount of ¹³¹I and of the Caesium isotopes ¹³⁴Cs and ¹³⁷Cs was measured in the XXX analysis center.

[0041] In the comparative example, the radioactive bark (Bark) used in Example A was washed with tap water.

[0042] The results are as follows:

[0043] The radiation dose before washing and after washing of A to C and comparative bark from sample A (bark) were measured.

[0044] The measurement method for nuclide measurement was carried out with gamma ray spectrometry using germanium semiconductor detector

[0045] The bark (Bark) of Examples A to C shows that the radiation dose of the radioactive bark is reduced to less than 200 Becquerel / kg or less, and it can be reused as a raw material for compost and soil conditioner.

Claims

1. Process for the decontamination of radioactively contaminated materials and products comprising the steps of

a) Providing radioactively contaminated materials and/or one or more products

b) Creating nanobubbles in water in at least one first reactor

c) Transferring the nanobubles in water in a second reactor comprising a thorium source

d) Applying pressure to the second reactor

e) Transferring the pressurized water with nanobubbles to a decontamination tank containing the radioactively contaminated material and/or products

2. Process according to claim 1, wherein the material is a natural organic material

3. Process according to claim 1 or 2, wherein the first reactor is a electrolytic cell

4. Process according to claim 3, wherein the water in the electrolytic cell has a ph > 7.

5. Process according to claim 4, wherein the electrolytic cell contains a cylindrical electrode comprising a plurality of rod-shaped electrodes.

6. Process according to one of the preceding claims wherein the thorium source are ceramic balls coated with Thorium or a thorium compound.

7. Process according to one of the preceding claims wherein the pressure applied in step d) is in the range from xy to XX[MS1].

8. Process according to claim 7, wherein the material and or products are treated in the contamination bath for a period of 0,25 to 1 h

9. Process according to claim 8, wherein the contamination bath comprises further a nanobubble source.

10. Process according to claim 9, wherein the nanobubbles are generated during the entire treatment of the materials and/or products in the contamination bath.

11. Radioactively decontaminated material and/or products obtainable by a process according to one of the preceding claims.

12. Electrode for use in a process according to one of claims 1 to 10, having a cylindrical housing with openings.

13. Electrode according to claim 12 wherein the electrode comprises at least 12 electrode rods arranged in the cylindrical housing.

Drawing