KR20220048882A - Chlorination-decontamination method for radioactive concrete waste - Google Patents

Abstract

The present invention relates to a chlorination decontamination method for treating radioactively contaminated concrete, and more particularly, to a decontamination method capable of minimizing the generation of secondary waste through chlorination treatment of concrete waste contaminated with radioactive nuclides. The decontamination method includes: a chlorination treatment process for soil contaminated with radioactive nuclides or concrete waste contaminated with radioactive nuclides at 600 to 1000℃; and a washing process.

Description

The chlorination decontamination method for the treatment of radioactively contaminated concrete {CHLORINATION-DECONTAMINATION METHOD FOR RADIOACTIVE CONCRETE WASTE}

The present invention relates to a chlorination decontamination method for the treatment of radioactively contaminated concrete, and more particularly, to a decontamination method capable of minimizing the generation of secondary waste through chlorination treatment of concrete waste contaminated with radionuclides.

In the preliminary evaluation of the nuclear power plant decommissioning source port and the amount of decommissioning waste generated in Korea, it was estimated that about 1,600 tons of low-level and ultra-low-level radioactive concrete waste were generated during the decommissioning of the Kori Unit 1 pressurized water reactor. This occupies a significant proportion of nuclear power plant decommissioning waste, and various studies on reduction of concrete waste are being conducted for the advancement of more economical and safe decommissioning technology. In general, a widely used method is a mechanical decontamination technique, which is a method of mechanically separating the surface parts, paying attention to the fact that the surface of the concrete waste has a relatively high degree of contamination. Since this method is not a precise decontamination technique, there is a clear limitation in terms of reduction efficiency, but it has the advantage of a simple process. Mechanical decontamination technology can be seen as a reduction technology at the level of roughly dividing concrete waste into a high-pollution part and a low-pollution part. Another method for treating concrete waste is chemical decontamination. In this case, it is a method of dissolving or adsorbing radionuclides on the surface and removing them by using an acidic solution, a surfactant, an organic solvent, etc. in stages or in combination. However, since this wet chemical decontamination process uses a solvent, secondary waste liquid is generated, and processes for its treatment are additionally needed.

Japanese Patent Laid-Open No. 2016-161422

An object of the present invention is to provide a decontamination technology capable of minimizing the generation of secondary waste through chlorination treatment of concrete waste contaminated with radionuclides or soil contaminated with radionuclides.

However, the technical problem to be achieved by the present invention is not limited to the above-mentioned problems, and other problems not mentioned will be clearly understood by those skilled in the art from the following description.

The present invention provides a chlorination treatment process at 600 to 1000 ° C. for concrete waste contaminated with radionuclides or soil contaminated with radionuclides; And it provides a decontamination method comprising a washing process. The method may further include sequentially a drying process and an evaporation process after the washing process.

The decontamination method proposed in the present invention utilizes a small amount of chlorine gas in treating the concrete waste contaminated with radionuclides, and the water used in the process is recycled in the process. It has the advantage of being extremely small. In addition, since a gas rather than a solution is used as a reactant, it is relatively easy to increase the capacity of the process device. Cs, Sr, and Co can be removed in a short time and with high efficiency through the dry chlorination decontamination technology presented in the present invention, which can reduce the load on the disposal of concrete waste, thereby bringing about a great economic effect in the field of decontamination and decontamination of nuclear power plants. In addition, the decontamination method according to the present invention has the advantage that it can be linked with the existing technology, so that it can be efficiently combined and operated according to the state of the waste. In addition, since this method is a technology that can be equally applied to soil contaminated with Cs, Sr, Co, etc. in addition to concrete waste, it can be used to restore a nuclear power plant site or to treat nuclear accident waste.

1 is a chlorination reduction process diagram of radioactive concrete waste.
2 is a result of analyzing the chlorination reaction tendency of radioactive concrete waste components.
3 schematically shows a method for manufacturing an eco-friendly aggregate according to the prior art (Republic of Korea Patent No. 10-2127491).
4 is a SrCl ₂ conversion ratio test results according to the chlorination reaction conditions of SrO.
5 is a crystal structure analysis result of SrO reacted with chlorine gas at 800 °C.

Hereinafter, the present invention will be described in detail.

Unless defined otherwise herein, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

Also, the singular forms used in the specification and appended claims may also be intended to include the plural forms unless the context specifically dictates otherwise.

Radioactive concrete waste accounts for a significant proportion of nuclear power plant decommissioning waste, and mechanical decontamination processes and wet chemical decontamination processes are generally performed to reduce concrete waste. However, since the mechanical decontamination process is not a precise decontamination technology, there is a limit in terms of reduction efficiency, and since the wet chemical decontamination process uses a solvent, there is a problem that secondary waste liquid is generated and additional processes are required for its treatment. Accordingly, an object of the present invention is to provide a decontamination method capable of efficiently reducing concrete waste contaminated with radionuclides through chlorination and minimizing the generation of secondary waste.

The present invention relates to a chlorination treatment process for concrete waste contaminated with radionuclides or soil contaminated with radionuclides; And it provides a decontamination method comprising a washing process. The method may further include sequentially a drying process and an evaporation process after the washing process.

The chlorination process may be a process of reacting with chlorine gas, and radionuclides may be converted into chloride by the chlorination process.

In the method, the radionuclide is converted into a chloride by the chlorination process, and the chloride can be dissolved in water during the washing process. In addition, most non-radioactive materials do not react with chlorine and can remain in solid form without being soluble in water during the washing process.

Accordingly, radioactive substances (chlorides) dissolved in water can be separated from non-radioactive substances in solid form. In this case, the solid non-radioactive material may be classified as low-level waste after water is removed through a drying process, and the liquid reactant may be subjected to an evaporation process to separate chloride.

The radionuclide may include one or more selected from the group consisting of Cs, Sr, and Co. The chloride may include at least one selected from the group consisting of CsCl, SrCl ₂ and CoCl ₂ .

The chlorination process may be performed at 600 to 1000 °C conditions. If it is less than 600 ℃, the chloride production efficiency may be insufficient, and if it exceeds 1000 ℃, the durability problem of the heating furnace may occur due to the use of corrosive chlorine gas.

The chlorination process may be performed for 0.5 to 8 hours, more specifically, 1 to 4 hours, but is not limited thereto.

In the chlorination process, chlorine gas may be supplied at a condition of 1 to 1000 mL/min, but is not limited thereto.

Hereinafter, the present invention will be described in more detail.

The method proposed by the present invention may consist of 1) chlorination treatment, 2) washing, 3) drying, and 4) evaporation. Concrete waste contaminated with radionuclides generated from dismantling of nuclear power plants is charged into a chlorination system and reacts with chlorine gas at 600 ~ 1000 ℃ conditions. At this time, Cs, Sr, Co, etc., which are major polluting nuclides, are converted into chlorides, and SiO ₂ , Al ₂ O ₃ etc., which are major components of concrete, do not react with chlorine and maintain an oxide form. In the case of Ca compounds, some are converted to chlorides. After the reaction, the residual chlorine is delivered to the exhaust gas treatment system for recycling or disposal. Concrete waste after chlorination is charged into a washing system and washed with water. At this time, CsCl, SrCl ₂ , CoCl ₂ , CaCl ₂ converted into chlorides in the previous chlorination process are dissolved in water and the oxides are solid. will retain its shape. Thus, the radioactive material is completely dissolved in water and separated from the solid, non-radioactive concrete constituents. Non-radioactive substances in solid form are then classified as low-level waste after water is removed through a drying process. On the other hand, the liquid reactant generated after washing is separated from chloride by evaporating water through an evaporation process. The evaporated water is circulated back to the washing process to minimize the generation of secondary waste. The chloride remaining after evaporation has a high concentration of radionuclides, so it is separately recovered and treated. At this time, the recovered radionuclides are recycled as isotopes as needed or undergo a process of being prepared and disposed of in a solid form.

In the present invention, the treatment temperature is limited to a relatively low region of 600 ~ 1000 ℃. This is so that the chlorides reacted during the chlorination treatment are not vaporized and remain as chlorides as in the prior art. In the case of the prior art, it is vaporized at the same time as the chloride is formed and then cooled, collected and separated, and the process temperature is set in a relatively high region for vaporization separation. However, when the process temperature exceeds 1000°C, durability problems may occur due to the use of corrosive chlorine gas.

Chloride is easy to vaporize, but also has high solubility in water. Therefore, in the present invention, since the present invention uses a method of converting to chloride by performing a low-temperature process, but not vaporizing, and then injecting water through a washing process to dissolve the chloride. no collection process is required.

In addition, as described in Example 2 below, when the reaction is carried out in the temperature range of the present invention, conversion to chloride occurs sufficiently and it is experimentally confirmed that it is easy to remove through washing, and as described in Example 1 Similarly, when a radionuclide reacts with chlorine gas to form a chloride, it is not vaporized and remains as a solid (vaporization temperature of chloride SrCl ₂ : 1250 ℃, CsCl: 1297 ℃, CoCl ₂ : 1049 ℃).

The configuration of the overall system of the present invention is shown in FIG. 1 . However, after one process, if the degree of decontamination does not satisfy the standard through dose evaluation, the removal rate of radionuclides can be improved by repeating the above process. It is possible to drive according to the characteristics.

Chlorination process

In the 'chlorination treatment' process, when radioactive concrete waste is charged, the temperature of the device is heated to 600~1000 ℃ for reaction. After that, chlorine gas is injected to convert the elements to be converted into chlorides. When the reaction is completed, the temperature of the device is lowered back to room temperature, and the radioactive concrete waste is moved to the cleaning device. Analysis of the reaction characteristics between the main components of radioactive concrete waste and chlorine gas was performed using thermodynamic data, and the results are shown in FIG. 2 . Here, when the Gibbs free energy is negative, it can be expected that the chloride formation reaction proceeds. As described above, it can be expected that non-radioactive elements and major components of concrete waste, such as Al ₂ O ₃ , SiO ₂ , and Fe ₂ O ₃ , whose Gibbs free energy value is positive over all temperatures, will not react with chlorine gas. On the other hand, in the case of Sr, Cs, and Co, which are major pollutants, it was confirmed that chloride was easily formed. At this time, it was found that chloride was formed in the case of Ca compound, which is one of the main components of concrete waste. From the above results, it can be confirmed that Sr, Cs, and Co, which are radioactive contaminants among various components in radioactive concrete waste, can be selectively converted into chloride through the chlorination process.

washing process

In the ‘washing’ process, water is injected into the radioactive concrete waste to dissolve the chloride, and the injected water uses the water recovered in the subsequent evaporation process. In the cleaning process, the cleaning efficiency can be improved through stirring or ultrasonication. Thereafter, a liquid phase in which chloride is dissolved and a solid phase insoluble in water are separated through solid-liquid separation. At this time, since all of the radionuclides were extracted in the liquid phase, the solid concrete waste is treated as a low-level or lower-level waste after drying. On the other hand, the liquid phase in which all radionuclides are dissolved moves to the 'evaporation' device to separate water. In the evaporator, water is evaporated using heating and vacuum, and the separated water is charged back into the washing process to minimize the generation of secondary waste. Chlorides that remain in solid form after evaporation go through a separate solidification and disposal process because they contain high concentrations of radionuclides.

If the radioactivity level of the low-pollution concrete waste recovered after the washing process is completed is insufficient, additional decontamination effect can be obtained by repeating the above process. Otherwise, the decontamination effect can be maximized.

Drying process and evaporation process

Radioactive materials are converted into chlorides such as CsCl, SrCl ₂ , CoCl ₂ , CaCl ₂ during the chlorination process and dissolved in water, and non-radioactive materials are maintained in a solid form. Accordingly, the radioactive material can be completely dissolved in water and separated from the solid non-radioactive material. Non-radioactive substances in solid form can be classified as low-level wastes after water is removed through a drying process, and the liquid reactants generated after washing are separated into chlorides by evaporation of water by an evaporation process.

As described above, this process can be used alone as well as in connection with the existing fixation. That is, in the existing multi-step complex contaminated concrete treatment method (refer to Korean Patent Registration No. 10-2127491, FIG. 3), a series of wet processes using an acid solution are performed after dry etching of concrete. In this case, there is a method of reducing the burden of a subsequent process by primarily removing contaminants by performing the chlorination dry decontamination process suggested in the present invention before dry etching. Alternatively, when replacing the wet etching process performed after concrete dry etching with the process presented in the present invention, a process without secondary acid waste solution may be configured.

Hereinafter, the present invention will be described in more detail through examples. Objects, features, and advantages of the present invention will be easily understood through the following examples. The present invention is not limited to the embodiments described herein, and may be embodied in other forms. The embodiments introduced herein are provided so that the spirit of the present invention can be sufficiently conveyed to those of ordinary skill in the art to which the present invention pertains. Therefore, the present invention should not be limited by the following examples.

<Example 1>

Among Cs and Sr, which are major polluting nuclides in concrete waste, it is reported that CsI, the main compound in spent fuel, has high solubility in water and reacts easily with chlorine gas. On the other hand, in the case of SrO, conversion reaction studies by chlorine gas have not been reported, but the fact that SrO is converted to SrCl ₂ by chlorine gas was confirmed through an experiment. SrCl ₂ is a highly soluble compound and can be easily removed by dissolving Sr in water in a subsequent washing process. In this example, about 1.2 g of SrO was charged into the quartz reactor, and reaction experiments were performed under various temperature and time conditions. In the experiment, 1.2 g of SrO was charged into an alumina crucible and placed in the center of a horizontally installed quartz reactor with a diameter of 4 cm. Thereafter, Ar was flowed at a flow rate of 300 mL/min for 2 hours or more to remove oxygen in the reactor, and then the temperature was raised at a rate of 10° C./min. When the temperature reached the target value, the reaction was started by switching the gas at a flow rate of 96 mL/min Ar + 4 mL/min Cl ₂ . When the target reaction time was reached, the injection of chlorine gas was stopped, the temperature of the reactor was lowered to room temperature, and the sample was recovered. Through the weight change before and after the reaction, the production rate of SrCl ₂ was confirmed. As shown in FIG. 4 , under the condition of 500 °C, SrCl ₂ production efficiency was low, so that only SrO of up to 10% or less was converted to SrCl ₂ . On the other hand, it can be confirmed that SrO is rapidly converted to SrCl ₂ at 600 ° C. or higher. After the reaction, crystal structure analysis of the product was performed through X-ray diffraction, and the results are shown in FIG. 5 . When the reaction time was 1 hour, a small amount of Sr ₄ OCl ₆ was observed together with SrCl ₂ , but as the reaction time increased, it was confirmed that only SrCl ₂ was formed. From this, it was confirmed that the conversion of SrO to SrCl ₂ using chlorine gas was possible at a temperature of 600 to 800 °C.

<Example 2>

A simulated concrete sample containing Cs, Sr, and Co was prepared, and the removal efficiency of each element through the chlorination process was reviewed. In this example, the concrete sample was immersed in an aqueous solution in which CsCl, SrCl ₂ , and CoCl ₂ were dissolved, and then the water was dried to evenly disperse the precursors of each element on the concrete surface. An experiment was performed using a quartz reactor as in Example 1 above using 0.6 g of simulated concrete powder. Reaction experiments were performed at 600 °C, 700 °C, 800 °C and 1000 °C, and the reaction time was fixed at 2 hours. At this time, the reaction gas was set to 96 mL/min Ar + 4 mL/min Cl ₂ . After the reaction was completed, the simulated concrete waste sample was mixed with 50 mL of water and maintained for 16 hours. Thereafter, filtering was performed to separate and recover liquid water and simulated concrete samples remaining in a solid phase. Inductively coupled plasma composition analysis was performed using the recovered solid simulated low-pollution concrete waste and washing solution to measure the separation efficiency, and the results are summarized in Table 1 below. As shown in Table 1, the removal rate of Cs, Sr, and Co increased as the reaction temperature increased. In particular, Sr was able to achieve a removal rate of 90% through the reaction at 600 °C. At 800°C, the removal rates of Cs and Sr exceeded 90%, and the removal rate of Co reached 84%. When the reaction temperature was increased to 1000 °C, the Co removal rate rose to 98%, confirming that all radionuclides were able to remove 95% or more.

reaction temperature reaction time Cs Removal Rate Sr Removal Rate Co removal rate 600℃ 2 hours 83% 90% 39% 700℃ 2 hours 82% 97% 48% 800℃ 2 hours 95% 97% 84% 1000℃ 2 hours 95% 97% 98%

Using the same experimental method as above, the Sr removal efficiency was reviewed while the reaction time was changed when the reaction temperature was 600 °C and 700 °C, and the results are shown in Table 2 below. As can be seen from the table, the Sr removal efficiency was 77-95% at 600°C, but showed a lower value on average compared to the 700°C condition. On the other hand, it was confirmed that a high Sr removal rate of 95% on average was confirmed at 700°C, and the change with time was insignificant. Therefore, it was confirmed that more than 95% of Sr could be removed with only a short reaction of 1 hour.

reaction temperature reaction time Sr Removal Rate 600℃ 1 hours 95% 2 hours 90% 4 hours 77% 700℃ 1 hours 95% 2 hours 97% 4 hours 93%

<Example 3>

As described above, the process proposed in the present invention can be used by mixing with the existing process. That is, when concrete is subjected to dry etching process, concrete is separated into large particles of 1 mm or more and small particles of 1 mm or less. In this example, after the dry etching process was performed using the simulated concrete sample described above, the dry chlorination decontamination process was performed using the separated sample to confirm the removal efficiency of contaminating nuclides.

A chlorination reaction was performed for 2 hours under the same conditions as above at 800° C., 96 mL/min Ar + 4 mL/min Cl ₂ , using fine powder of 1 mm or less, and composition analysis of the recovered solid concrete sample and washing solution was performed. Thus, the results are shown in Table 3 below. As can be seen from the table, it can be seen that the removal rate of each element increases as the reaction temperature increases. After the reaction at 800 °C, the removal rate of Cs reached 95%, and it was confirmed that the removal rates of Sr and Co reached 88% and 76%, respectively. In the case of carrying out such a linked process, since large particles of 1 mm or more occupying a large volume are separated in advance through a simple dry etching process, the amount of reactants input to the chlorination decontamination process is greatly reduced, which greatly reduces the burden on the process. do. In addition, it can be confirmed that if the wet process proposed in the previous invention is replaced by the dry chlorination decontamination process proposed in the present invention, it is possible to easily remove major radionuclides without generating a secondary waste solution.

reaction temperature reaction time Cs Removal Rate Sr Removal Rate Co removal rate 600℃ 2 hours 67% 86% 61% 700℃ 2 hours 86% 87% 68% 800℃ 2 hours 95% 88% 76%

Table 4 below shows the results of measuring Sr removal rates according to reaction time at 600°C and 700°C using fine powders of 1 mm or less. The difference in the Sr removal rate according to temperature was not significant, but in both cases, the highest Sr removal efficiency was exhibited during the 2 hour reaction. In addition, it was confirmed that at least 80% or more of Sr could be removed under any conditions.

reaction temperature reaction time Sr Removal Rate 600℃ 1 hours 81% 2 hours 86% 4 hours 80% 700℃ 1 hours 82% 2 hours 87% 4 hours 84%

Claims (7)

Chlorination treatment process at 600 to 1000 ℃ conditions for concrete waste contaminated with radionuclides or soil contaminated with radionuclides; and a decontamination method comprising a washing process.
According to claim 1,
The radionuclide is a decontamination method, characterized in that it comprises at least one selected from the group consisting of Cs, Sr and Co.
According to claim 1,
Decontamination method, characterized in that the radionuclide is converted into chloride by the chlorination process.
4. The method of claim 3,
The chloride is CsCl, SrCl ₂ and CoCl ₂ Decontamination method, characterized in that it comprises at least one selected from the group consisting of.
According to claim 1,
The chlorination process is a decontamination method that is a process of reacting with chlorine gas.
According to claim 1,
In the above method, by the chlorination process, the radionuclide is converted into a chloride, and the chloride is dissolved in water during the washing process.
According to claim 1,
The method further comprises sequentially a drying process and an evaporation process after the washing process.

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