Apparatus and method for treating contaminated water containing radioactive materials

Abstract

To provide a device and a method for treating contaminated water containing radioactive substances, which allow for performing stable treatment and coping with fluctuations in isotope mass concentration of radioactive substances in treatment target water.SOLUTION: A device for treating contaminated water containing a radioactive substance is provided, comprising a monitoring unit for monitoring isotope mass concentration of a radioactive substance in contaminated water to be treated, an adder unit configured to add a nonradioactive substance of the same element as the radioactive substance when monitoring done by the monitoring unit reveals that the isotope mass concentration is less than a lower threshold, and an adsorption tower containing an adsorbent for adsorbing the radioactive substance.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] An embodiment of the present invention relates to an apparatus and method for treating contaminated water containing radioactive materials. [Background technology]

[0002] At the Fukushima Daiichi Nuclear Power Plant, the concentration of radioactive materials in the water being treated for contaminated water treatment was highest immediately after the accident and has been decreasing over the years. The concentration of radioactive materials in the water being treated is expected to continue to decrease in the future, but there is a possibility that the water quality will fluctuate irregularly, for example, if the water dries up and the contaminated water remaining at the bottom of the building is withdrawn.

[0003] In contaminated water treatment using the water flow method using an adsorption tower, if the isotope mass concentration of radioactive substances in the water being treated changes from a high condition to a low condition, there is a concern that the adsorption equilibrium point will shift, the saturated adsorption amount will decrease, and the adsorbed radioactive substances will be desorbed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-75245 A Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in the treatment of contaminated water containing radioactive materials using a water flow method using an adsorbent, if the isotope mass concentration of the radioactive material in the water being treated changes from a high condition to a low condition, there is a concern that the saturated adsorption amount will decrease and the adsorbed radioactive material will be desorbed. For example, at the Fukushima Daiichi Nuclear Power Plant, where drying up is progressing, there is a good chance that the water quality of the water being treated will fluctuate irregularly in the future, and it is desirable to be able to respond to such fluctuations in water quality.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide an apparatus and method for treating contaminated water containing radioactive substances that can respond to fluctuations in the isotope mass concentration of radioactive substances in the water to be treated and can perform stable treatment. [Means for solving the problem]

[0007] The apparatus for treating contaminated water containing radioactive substances according to an embodiment includes a monitoring unit that monitors an isotope mass concentration of the radioactive substance in the contaminated water to be treated, an addition unit that adds a non-radioactive substance of the same element as the radioactive substance when the isotope mass concentration is lower than a lower limit as a result of monitoring by the monitoring unit, and an adsorption tower into which an adsorbent that adsorbs the radioactive substance is introduced. an injection unit that injects water when the isotope mass concentration is higher than an upper limit value as a result of monitoring by the monitoring unit; The present invention is characterized in that it is provided with: Effect of the Invention

[0008] According to an embodiment of the present invention, it is possible to provide an apparatus and method for treating contaminated water containing radioactive substances that can respond to fluctuations in the isotope mass concentration of radioactive substances in the water to be treated and can perform stable treatment. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of a first embodiment. [Diagram 2] FIG. 4 is a flowchart showing a process flow in the first embodiment. [Diagram 3] FIG. 11 is a diagram illustrating a schematic configuration of a second embodiment. [Figure 4] FIG. 11 is a flowchart showing a process flow in the second embodiment. [Diagram 5] FIG. 13 is a diagram illustrating a schematic configuration of a third embodiment. [Figure 6] FIG. 1 shows examples of high and low strontium concentrations. [Figure 7] FIG. 13 is a diagram showing an example of the adsorption and desorption amounts of strontium when the concentration changes from high to low. [Figure 8] FIG. 4 is a diagram showing an example of the adsorption ratio of radioactive strontium in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an apparatus and method for treating contaminated water containing radioactive materials according to an embodiment will be described with reference to the drawings.

[0011] (First embodiment) First, the first embodiment will be described with reference to Figures 1 and 2. Figure 1 is a diagram showing a schematic configuration of this embodiment, and Figure 2 is a flow diagram showing the process flow of the first embodiment. In Figure 1, 1 is water to be treated that contains radioactive substances, 2 is a monitoring section, 3 is a non-radioactive same element addition section, 4 is an adsorption tower, and 5 is treated water.

[0012] 1 and 2, in this embodiment, the concentration of the substance to be removed contained in the treatment target water 1 containing radioactive substances is monitored by a monitoring unit 2 (step 101 in FIG. 2). In the monitoring unit 2, for example, a part of the treatment target water 1 is sampled, and the concentration of the substance to be removed contained therein (isotope mass concentration of the radioactive substance) is measured by, for example, ICP analysis or the like.

[0013] Then, if monitoring by the monitoring unit 2 detects a concentration lower than the lower limit of a certain target isotope mass concentration set in consideration of actual operation (Yes in step 102 of FIG. 2), the non-radioactive same element addition unit 3 adds a non-radioactive substance of the same element as the radioactive substance to be removed so as to achieve the target isotope mass concentration (step 103 of FIG. 2).

[0014] At this time, the upper limit of the concentration of the non-radioactive substance added is the maximum concentration at which no precipitation occurs due to the addition of the non-radioactive substance and Henry's law holds. The water to be treated 1, in which the isotope mass concentration of the element to be removed has become constant, is passed through the adsorption tower 4 filled with an adsorbent that adsorbs radioactive substances (step 104 in FIG. 2), and becomes treated water 5 from which the radioactive substances have been removed. On the other hand, if a concentration lower than the lower limit of the target isotope mass concentration is not detected (No in step 102 in FIG. 2), the water is passed through the adsorption tower 4 as is.

[0015] Radioactive substances to be removed include, for example, potassium, manganese, krypton, technetium, lead, polonium, radon, radium, thorium, cesium, strontium, ruthenium, iodine, cobalt, and bismuth.

[0016] The operation of the first embodiment having the above configuration will be described below. In the adsorption treatment of contaminated water containing radioactive substances, if the isotope mass concentration of the radioactive substances in the water to be treated changes from a high condition to a low condition, there is a concern that the saturated adsorption amount will decrease and the radioactive substances adsorbed in the adsorption tower 4 will be desorbed.

[0017] This is because, under conditions where Henry's law holds, the saturated adsorption amount of radioactive materials adsorbed to the adsorbent by the flow-through method of contaminated water treatment is shown by the solid phase concentration W in the following (Equation 1), and the saturated adsorption amount of the adsorbent decreases when the inlet concentration of the adsorption tower 4 decreases. At Fukushima Daiichi Nuclear Power Plant, where drying up is progressing, there is a good chance that the water quality of the water to be treated will fluctuate irregularly, and it is desirable to respond to such fluctuations in water quality. W (solid phase concentration) = Kd (distribution coefficient) × C (liquid phase concentration) ... (Equation 1)

[0018] In this embodiment, a non-radioactive substance of the same element as the radioactive substance to be removed is added, and the isotope mass concentration in the water to be treated is kept constant, thereby suppressing fluctuations in water quality and preventing desorption of the radioactive substance from the adsorbent. The adsorbent used is an ion adsorbent, which adsorbs the same element regardless of whether it is radioactive or non-radioactive, so by keeping the isotope mass concentration of the substance to be removed constant, the liquid phase concentration C of the water passed through the adsorption tower 4 in (Equation 1) can be kept constant, making it possible to suppress desorption of the radioactive substance without changing the saturated adsorption amount.

[0019] The operation method is to first set a lower limit for the target isotope mass concentration of radioactive materials in the water to be treated based on operational records. As a rule, the average concentration during a given monitored period is set as the target isotope mass concentration, and the lower limit is set. If the concentration fluctuates significantly, the target concentration is adjusted as appropriate.

[0020] Next, the isotope mass concentration of the radioactive substance in the contaminated water is monitored by monitoring section 2. If the concentration confirmed here falls below the lower limit of the target isotope mass concentration, and there is concern that the saturated adsorption amount of the adsorbent will decrease, a non-radioactive substance is added from non-radioactive identical element addition section 3 to suppress desorption of the radioactive substance from the adsorbent.

[0021] The concentration of the non-radioactive substance added is set to the maximum concentration at which no precipitation occurs due to the addition of the non-radioactive substance and Henry's law holds. This makes it possible to obtain an effect while suppressing the formation of precipitation due to the addition of a large amount of non-radioactive substance and the shortening of the breakthrough time when the substance is added under conditions where Henry's law does not hold. At this time, the monitoring unit 2 records the total amount of treated water passed through the adsorption tower 4 and the concentrations of the radioactive substance and the added non-radioactive isotope, and grasps the adsorption amount of the radioactive substance and non-radioactive isotope already adsorbed in the adsorption tower 4.

[0022] As an example of an operating method, in contaminated water treatment using a strontium adsorbent, a case will be described in which the water to be treated 1 with a high strontium concentration (1 ppm) shown in Figure 6 is passed through the adsorption tower 4, and as adsorption progresses, the concentration at the adsorption tower outlet becomes the same as the concentration at the adsorption tower inlet, and the water quality of the water to be treated 1 changes to a low strontium concentration (0.14 ppm).

[0023] The distribution coefficient Kd in the above-mentioned (Equation 1) is a value that varies depending on the concentration of radioactive materials and seawater components in the treated water 1, and the distribution coefficient Kd was obtained by actual testing under water quality conditions that mimicked the assumed treated water 1. The test conditions were based on 50-fold diluted seawater with a calcium concentration adjusted to 30 ppm, and a column test was performed with a strontium concentration of 1 ppm.

[0024] As a result, the partition coefficient Kd is about 2 × 10 4 Under conditions where Henry's law holds, the distribution coefficient Kd is constant regardless of the liquid phase concentration C, so this result was used to calculate the adsorption amounts at strontium concentrations of 1 ppm and 0.14 ppm from (Equation 1), and the desorption amount from the adsorbent when the concentration changed from 1 ppm to 0.14 ppm was estimated, as shown in Figure 7.

[0025] By applying this embodiment under these fluctuating water quality conditions and monitoring the concentration of radioactive substances in the contaminated water, it becomes possible to suppress fluctuations in the saturated adsorption amount and prevent desorption of radioactive substances by adding non-radioactive strontium of the same element so that the total amount of strontium isotopes becomes 1 ppm after the application.

[0026] In this embodiment, the addition of non-radioactive substances causes the adsorbent to adsorb an amount of strontium equivalent to the amount that would normally be desorbed from the adsorbent. At this time, the amount of radioactive strontium adsorbed in this embodiment is estimated to be the total amount of strontium adsorbed multiplied by the concentration ratio of radioactive strontium in the water to be treated, as shown in (Equation 2). Therefore, under conditions in which the strontium concentration in the contaminated water varies from 1 ppm to 0.14 ppm, the proportion of the adsorbed strontium that is radioactive is as shown in Figure 8. The adsorption proportion of radioactive substances is 12% of the total mass concentration of strontium including non-radioactive substances, and it is possible to adsorb radioactive substances while obtaining the effect of suppressing desorption from the adsorbent.

[0027] Amount of radioactive strontium adsorbed in the embodiment [mol / g] = Total amount of strontium adsorbed in the embodiment [mol / g] × Radioactive strontium weight concentration [ppm] / total strontium weight concentration [ppm] ...(Formula 2) (Total Strontium = Radioactive Strontium + Non-Radioactive Strontium)

[0028] According to the first embodiment of the present invention, the following effects can be obtained. (1) In contaminated water treatment systems that adsorb and remove radioactive substances, adding a non-radioactive substance of the same element as the radioactive substance and keeping the isotope mass concentration of the substance to be removed in the water to be treated constant makes it possible to suppress the desorption of radioactive substances adsorbed to the adsorbent. (2) By installing a section for monitoring the isotope mass concentration of radioactive substances in the water to be treated upstream of the section for adding non-radioactive substances, it becomes possible to respond promptly to fluctuations in the isotope mass concentration of radioactive substances in the water to be treated. (3) The concentration of the non-radioactive substance to be added is limited to the maximum concentration at which no precipitate is formed and Henry's law holds. This makes it possible to obtain the above-mentioned effects while suppressing the formation of precipitates and shortening the time to breakthrough due to the addition of non-radioactive substances.

[0029] Second embodiment Next, a second embodiment will be described with reference to Fig. 3 and Fig. 4. Fig. 3 is a diagram showing a schematic configuration of the second embodiment, and Fig. 4 is a flow diagram showing a process flow of the second embodiment. In Fig. 3 and Fig. 4, parts corresponding to those of the first embodiment shown in Fig. 1 and Fig. 2 are given the same reference numerals and duplicated explanations will be omitted.

[0030] As shown in Fig. 3, in the second embodiment, a filtrate injection unit 6 is provided in addition to the configuration of the first embodiment shown in Fig. 1. In this second embodiment, similarly to the first embodiment, when a concentration lower than a lower limit value of a certain target isotope mass concentration set in consideration of actual operation is detected by monitoring in the monitoring unit 2, a non-radioactive substance of the same element as the radioactive substance to be removed is added from the non-radioactive same element addition unit 3 so as to reach the target isotope mass concentration.

[0031] On the other hand, when a concentration higher than the upper limit set based on the target isotope mass concentration is detected by monitoring in the monitoring unit 2 (Yes in step 105 in FIG. 4), filtered water or the like is injected from the filtered water injection unit 6 to dilute the water (step 106 in FIG. 4). As a result, the water to be treated 1, in which the isotope mass concentration of the element to be removed has become constant, is passed through the adsorption tower 4 filled with an adsorbent that adsorbs radioactive substances, and becomes treated water 5 from which the radioactive substances have been removed. On the other hand, when a concentration higher than the upper limit of the target isotope mass concentration is not detected (No in step 105 in FIG. 4), the water is passed through the adsorption tower 4 as is. Radioactive substances to be removed include potassium, manganese, krypton, technetium, lead, polonium, radon, radium, thorium, cesium, strontium, ruthenium, iodine, cobalt, bismuth, and the like, as in the first embodiment.

[0032] The operation of the second embodiment having the above configuration will be described below. In the second embodiment described above, similarly to the first embodiment, when the isotope mass concentration of a radioactive substance in the water to be treated changes from a high condition to a low condition, non-radioactive substances of the same element are added up to the target isotope mass concentration to suppress fluctuations in the water quality of the water to be treated, thereby suppressing desorption of the radioactive substance from the adsorbent.

[0033] Furthermore, when the isotope mass concentration of radioactive materials in the water to be treated changes from a low condition to a high condition, the adsorption equilibrium is similarly shifted and the saturated adsorption amount decreases, which may cause fluctuations in the removal performance of the adsorption tower 4. At nuclear power plants, conditions under which significantly high isotope mass concentrations are monitored are predicted to be temporary and limited, such as when contaminated water remaining at the bottom of the building is taken in, and when normal low-concentration contaminated water is passed through these conditions, there is a possibility that a large amount of radioactive materials will be desorbed from the adsorbent.

[0034] Therefore, when contaminated water with a concentration higher than the upper limit preset based on the target isotope mass concentration is monitored, filtered water or the like is injected to dilute the water to the target isotope mass concentration. This makes it possible to maintain a stable removal performance of the adsorption tower 4 by suppressing fluctuations in water quality.

[0035] As described above, according to the second embodiment, the same effects as those of the first embodiment can be obtained, and by additionally providing a configuration for injecting filtered water or the like for dilution when a high isotope mass concentration is monitored, it becomes possible to suppress fluctuations in water quality over a wide concentration range and stabilize the removal performance of the adsorption tower 4. Note that, although the present embodiment has been described as an example in which filtered water is used for dilution, it is also possible to dilute the water using water from a separate system.

[0036] Third embodiment Next, a third embodiment will be described with reference to Fig. 5. Fig. 5 shows the configuration of the third embodiment, and parts corresponding to those of the first embodiment shown in Fig. 1 and the second embodiment shown in Fig. 3 are given the same reference numerals and will not be described again.

[0037] As shown in Fig. 5, in the third embodiment, a second adsorption tower 7 is provided in addition to the configuration of the second embodiment shown in Fig. 3. The number of adsorption towers is not limited to two, and may be greater. In this third embodiment, as in the first embodiment, when a concentration lower than the lower limit of the target isotope mass concentration set in consideration of actual operation is detected by monitoring in the monitoring unit 2, a non-radioactive substance of the same element as the radioactive substance to be removed is added from the non-radioactive same element addition unit 3 so as to reach the target isotope mass concentration.

[0038] On the other hand, if monitoring in the monitoring unit 2 detects a concentration higher than the upper limit of the target isotope mass concentration, filtered water or the like is injected from the filtered water injection unit 6 to dilute the water. As a result, the water to be treated 1, whose isotope mass concentration of the element to be removed has become constant, is passed through the adsorption tower 4 filled with an adsorbent that adsorbs radioactive substances, and becomes treated water 5 from which the radioactive substances have been removed.

[0039] Furthermore, if a change in water quality is confirmed by the monitoring unit 2, water can be passed through the second or subsequent adsorption tower 7. For example, in the case of a normal concentration, water is passed through the adsorption tower 4, and in the case of monitored contaminated water with a lower (or higher) concentration than normal, the water is switched to be passed through the adsorption tower 7. As in the first embodiment, radioactive substances to be removed include potassium, manganese, krypton, technetium, lead, polonium, radon, radium, thorium, cesium, strontium, ruthenium, iodine, cobalt, bismuth, and the like.

[0040] The operation of the third embodiment will be described below. In the above-described third embodiment, as in the first embodiment, when the isotope mass concentration of a radioactive substance in the water to be treated changes from a high condition to a low condition, a non-radioactive substance of the same element is added up to the target isotope mass concentration to suppress fluctuations in the water quality of the water to be treated, thereby suppressing desorption of the radioactive substance from the adsorbent.

[0041] In addition, similarly to the second embodiment, when contaminated water with a higher isotope mass concentration than the target isotope mass concentration is monitored, filtered water or the like is injected to dilute the water to the target isotope mass concentration. This makes it possible to maintain a stable removal performance of the adsorption tower 4 by suppressing water quality fluctuations.

[0042] Furthermore, when a change in water quality is confirmed, the influence of the change in water quality in the first adsorption tower 4 can be suppressed by switching to one of the second and subsequent adsorption towers 7 and passing water through it. In this case, for example, a large change in water quality can be dealt with by adding a non-radioactive substance of the same element or injecting filtered water, and a small change in water quality can be dealt with by switching to the adsorption tower 7. At this time, the second and subsequent adsorption towers 7 also record the total amount of treated water already passed through, water quality conditions such as radioactive substances and seawater components, etc. in the monitoring unit 2 in the same way as the first adsorption tower 4, grasp the amount of adsorption that has already been adsorbed, and pass water through the adsorption tower 7 without being affected by desorption, etc.

[0043] By switching between multiple adsorption towers 4, 7 in response to fluctuations in water quality, it is possible to suppress fluctuations in the water quality of the treatment water 1 passing through each of the adsorption towers 4, 7, enabling more stable operation of the adsorption towers 4, 7. As with the adsorption tower 4, the second and subsequent adsorption towers 7 also have a target isotope mass concentration set, and if a concentration fluctuation is confirmed, non-radioactive substances can be added, or the concentration can be diluted by injecting filtered water, or the adsorption tower can be switched to the next or subsequent towers.

[0044] As described above, according to the third embodiment, the same effects as those of the first and second embodiments can be obtained, and by providing a line that switches water flow to the second or subsequent adsorption towers 7 when a change in water quality is confirmed by the monitoring unit 2, it is possible to suppress water quality changes over a wide concentration range and stabilize the removal performance of the adsorption towers 4.

[0045] Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, and combinations can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0046] 1...Water to be treated containing radioactive substances, 2...Monitoring section, 3...Non-radioactive same element addition section, 4...Adsorption tower, 5...Treated water, 6...Filtered water injection section, 7...Adsorption towers from the second tower onwards.

Claims

1. A monitoring unit that monitors the isotope mass concentration of radioactive materials in the contaminated water to be treated; an addition unit that adds a non-radioactive substance of the same element as the radioactive substance when the isotope mass concentration is lower than a lower limit as a result of monitoring by the monitoring unit; An adsorption tower that contains an adsorbent that adsorbs radioactive materials; an injection unit that injects water when the isotope mass concentration is higher than an upper limit value as a result of monitoring by the monitoring unit; 1. A treatment apparatus for contaminated water containing radioactive materials, comprising:

2. A treatment device for contaminated water containing radioactive materials according to claim 1, The adsorption tower includes at least a first adsorption tower and a second adsorption tower, An apparatus for treating contaminated water containing radioactive substances, characterized in that it is possible to switch between passing water through the first adsorption tower or the second adsorption tower depending on the results of monitoring by the monitoring unit.

3. A monitoring step of monitoring the isotope mass concentration of radioactive materials in the contaminated water to be treated; an addition step of adding a non-radioactive substance of the same element as the radioactive substance to the contaminated water to be treated when the isotope mass concentration is lower than a lower limit as a result of the monitoring step; After the adding step, a step of passing the contaminated water to be treated through an adsorption tower containing an adsorbent that adsorbs radioactive materials; an injection step of injecting water into the contaminated water when the isotope mass concentration is higher than an upper limit value as a result of the monitoring step; A method for treating contaminated water containing radioactive substances, comprising:

4. A method for treating contaminated water containing radioactive materials according to claim 3, A method for treating contaminated water containing radioactive substances, characterized in that the concentration of the non-radioactive substance of the same element as the radioactive substance added in the adding step is limited to the maximum concentration at which no precipitation is formed by the addition and Henry's law holds.

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