JP2016118398A - Decontamination treatment method for contaminated water storage tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decontamination treatment method for a contaminated water storage tank, which enables a radiation level in a contaminated water storage tank to be reduced at relatively low cost and easily without causing increase in the quantity of contaminated water.SOLUTION: The decontamination treatment method for a contaminated water storage tank is provided that is for use in n (n is two or more) tanks in which contaminated water containing radioactive substance is stored. The method comprises a first step of discharging contaminated water from a first storage tank, clarifying and introducing it to a substitute tank and a second step of discharging contaminated water from a k-th storage tank, clarifying and causing it to flow into a k-1-th storage tank, and the second step is repeated until k, which is 2 at first, reaches n. It is preferable that the method further comprises a third step of introducing low-concentration contaminated water in the storage tank after having been used in the second step to the substitute tank. It is also preferable that the method further comprises a fourth step of causing the low-concentration contaminated water in the storage tank after having been used in the second step or water in the substitute tank to flow in the n-th storage tank after having been used in the second step, and introducing diluted low-concentration contaminated water to the substitute tank.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a decontamination processing method for a contaminated water storage tank.

  Contaminated water containing radioactive substances such as radioactive cesium and radioactive strontium, such as waste water, accident core water cooling circulation water, etc., is not allowed to be discharged unless the radioactive substances are removed in order to prevent environmental destruction.

  For this reason, in the accident nuclear power plant, the contaminated water which collected surplus reactor cooling water etc. is stored in many storage tanks, and the quantity is increasing every day. Many of these storage tanks are bolt-tight tanks formed by joining a plurality of plate-like members on-site by bolting. In such a bolt-clamped tank, leakage may occur due to deterioration of the packing or the like of the fastening portion between the members.

  Therefore, it is desirable to replace such a bolted tank with a welded tank that is formed by welding a plurality of plate-like members and has a longer life. However, even if polluted water is discharged from the bolted tank, the bolts must be further decontaminated due to radioactivity adhering to the inner wall of the tank and contaminated water remaining between the bolt fastening flanges at the bottom of the tank. The clamped tank cannot be easily dismantled.

The typical radioactive substance content of the contaminated water stored in such a storage tank is considered to be on the order of 100,000 Bq / cc, and even if the internal contaminated water is discharged, the inner wall surface of the storage tank In this state, a radioactive substance is attached, and as a radioactivity level, the surface contamination concentration is expected to be about 1,000 Bq / cm ² . In this case, since the radiation dose is too large and the exposure amount of the worker who performs the dismantling operation reaches the exposure limit in a short time, it is not realistic to dismantle a large number of storage tanks as they are after discharging contaminated water.

  Therefore, it is considered to decontaminate the storage tank after discharging the contaminated water after decontamination of the inner wall surface. However, the decontamination work is also very difficult due to the exposure of workers as well as the demolition work. It is. Therefore, it is desired to decontaminate the inner wall surface of the storage tank without an operator entering the storage tank.

  As a suggestion, if new water, which is non-polluted water, is supplied to a storage tank that has discharged polluted water, the radioactivity level can be further reduced. However, when non-contaminated water is used, new contaminated water is generated even at a low concentration, and its treatment becomes a problem. Therefore, it is not preferable to decontaminate the storage tank using non-contaminated water.

  Further, even if the storage tank having such a high contamination level can be disassembled without decontamination, the dismantled material such as the disassembled steel plate has a high surface contamination concentration, and the disposal method becomes a problem.

  Also, as a method of dismantling radioactive contamination facilities, a roof that covers the radioactive contamination facilities is constructed, a remotely operable crane is installed near the ceiling of the roof, and a person using this crane can use it. It has been proposed to dismantle and decontaminate equipment without entering the indoor area (see, for example, JP-A-2013-181921). However, the construction of a roof requires a large cost, and a large number of storage tanks are densely arranged at the accident nuclear power plant, so that the construction of a roof is extremely difficult technically.

JP2013-181921A

  In view of the above inconveniences, the present invention provides a decontamination treatment method for a contaminated water storage tank that can easily reduce the radioactivity level of the contaminated water storage tank while suppressing an increase in the amount of contaminated water. Let it be an issue.

  The invention made in order to solve the above-mentioned problem is a decontamination processing method for n storage tanks (n is 2 or more) in which contaminated water containing radioactive substances is stored, and the contaminated water is discharged from the first storage tank. And a second step of discharging and purifying the contaminated water from the kth storage tank and flowing into the k−1th storage tank, and the second step. It is a decontamination processing method of a contaminated water storage tank characterized by repeating a process from k to 2 to n.

  The method for decontamination of the contaminated water storage tank is to first supply the contaminated water by flowing purified water obtained by purifying the contaminated water discharged from the next storage tank into the storage tank from which the contaminated water was discharged first. Dilute radioactive material remaining in the drained storage tank. Thereby, the radioactivity level of the 1st to (n-1) th storage tank can be reduced comparatively cheaply and easily, without using new water and increasing the amount of contaminated water. “Purified water” means contaminated water whose radioactive substance content has been reduced by purification, and does not require purification to such an extent that it can be discharged outside a management area such as the ocean.

  It is preferable to further include a third step of introducing the low concentration contaminated water in the storage tank after the second step into the alternative tank. In this manner, the storage tank can be disassembled by discharging the low-concentration contaminated water in the storage tank whose radioactivity level has been reduced in the second step.

  The low concentration contaminated water in the storage tank after the second step or the water in the alternative tank flows into the nth storage tank after the second step, and the diluted low concentration contaminated water is introduced into the alternative tank. A fourth step may be further provided. In this way, the low-concentration contaminated water obtained by diluting the contaminated water in the storage tank in the second step or the purified water or low-concentration contaminated water introduced into the alternative tank in the first step or the third step is finally used for contamination. By diluting the radioactive material remaining in the storage tank that drained the water, the radioactivity level of the last storage tank can be lowered relatively cheaply and easily without using new water to increase the amount of contaminated water Can do.

  The contaminated water may be discharged by a pump, and from a predetermined water level, a low water level pump may be used. In this way, the amount of contaminated water remaining at the bottom of the storage tank can be reduced by discharging the contaminated water using a pump and starting from a predetermined water level using a low water level pump. Dilution of radioactive materials with contaminated water is more reliable. In addition, since the amount of purified water or low-concentration contaminated water introduced for dilution can be reduced, the cost and time for discharging low-concentration contaminated water before dismantling the diluted storage tank can be reduced. can do.

  The storage tank may be a member in which a plurality of members are fastened by bolting, and the alternative tank may be a member in which a plurality of members are joined by welding. In this way, by reducing the radioactivity level of the bolted storage tank having a relatively short life, and flowing the remaining purified water or low-concentration contaminated water into the welded tank having a relatively long life, the tank The spread of contamination due to leakage of water can be prevented.

  For the purification, it is preferable to use one or a plurality of adsorption towers that are mounted on a movable frame and are filled with an adsorbent that selectively adsorbs strontium. As described above, by using the adsorption tower mounted on the movable gantry, the contaminated water purification facility can be easily and reliably disposed near the storage tank. In addition, by using an adsorption tower filled with an adsorbent that selectively adsorbs strontium, it is processed by SARRY (Simply Active Water Retrieve and Recovery System) or the like and stored in a storage tank. It is possible to efficiently remove strontium occupying most of the radioactive material remaining in the contaminated water, thereby reducing the radioactivity level more reliably. The “stand” means a base on which the adsorption tower is disposed, and includes a plate or frame having a small height.

  The inflow of purified water into the storage tank may be performed so as to generate turbulent flow in the storage tank. In this way, by generating turbulent flow in the storage tank due to the inflow of purified water, radioactive substances adhering to the inner wall surface of the storage tank can be efficiently washed away and diluted to reduce the radioactivity level more reliably. It is done.

  As described above, the decontamination processing method for a contaminated water storage tank according to the present invention can lower the radioactivity level of the contaminated water storage tank relatively easily and inexpensively without increasing the amount of contaminated water.

It is a schematic diagram which shows the contaminated water storage tank to which the decontamination processing method of the contaminated water storage tank of one Embodiment of this invention is applied, the alternative tank used for a decontamination process, and contaminated water purification equipment. It is a schematic diagram which shows the detailed structure of the contaminated water purification equipment of FIG. It is a flowchart which shows the procedure of the decontamination processing method of the contaminated water storage tank of one Embodiment of this invention. It is a schematic diagram explaining the 1st process of FIG. It is a schematic diagram explaining the first cycle of the 2nd process of FIG. It is a schematic diagram explaining the next cycle of the 2nd process of FIG. It is a schematic diagram explaining the last cycle of the 2nd process of FIG. It is a schematic diagram explaining the first cycle of the 3rd process of FIG. It is a schematic diagram explaining the last cycle of the 3rd process of FIG. It is a schematic diagram explaining the first process of the 4th process of FIG. It is a schematic diagram explaining the process following FIG. 10 of the 4th process of FIG. It is a schematic diagram explaining the example which performs the 2nd process and 3rd process of FIG. 3 simultaneously.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
FIG. 1 shows storage tanks Ts1 to Ts4 that are decontaminated by the decontamination processing method for a contaminated water storage tank according to an embodiment of the present invention, and alternative tanks Tr1 to Tr1 that are used in the decontamination processing method for the contaminated water storage tank. Tr4 and contaminated water purification equipment U are typically shown. In the figure, the contaminated water is hatched, and the higher the contamination level, the larger the hatching density.

  The decontamination processing method for the contaminated water storage tank is a decontamination processing method for n storage tanks (n is 2 or more) in which contaminated water containing radioactive substances is stored. In the following description, FIG. As shown, an example in which n = 4, that is, the decontamination process of the four storage tanks Ts1 to Ts4 is performed. In the present embodiment, the pump P discharges contaminated water from the storage tanks Ts1 to Ts4 and the alternative tanks Tr1 to Tr4.

(Contaminated water)
The contaminated water stored in the storage tanks Ts1 to Ts4 to which the storage tank decontamination processing method is applied includes a certain amount of radioactive material. Even if the contaminated water is drained, the storage tanks Ts1 to Ts4 It is assumed that the surface contamination density contains a radioactive substance at a concentration that is expected to exceed the surface density limit (4 Bq / cm ² for α-ray emitting nuclides and 40 Bq / cm ² for nuclides other than α-emitting nuclides). The concentration of radioactive material in such contaminated water is not particularly limited, but as a guide, it is 10,000 Bq / cc or more, typically 100,000 Bq / cc or more.

(Storage tank)
The storage tanks Ts1 to Ts4 are not particularly limited. However, the storage tanks Ts1 to Ts4 are assumed to be contaminated water tanks that are dismantled and disposed of, and are particularly assumed to be contaminated water tanks that need to be disposed of due to a short remaining life. The As such a contaminated water tank that needs to be disposed of, typically, there is a bolted tank in which a plurality of members having flanges arranged on the periphery of a plate material are fastened by bolting.

Further, the volume of the storage tanks Ts1 to Ts4 is not particularly limited, but is generally 100 m ³ or more, typically 1,000 m ³ or more. When the volume of the storage tanks Ts1 to Ts4 is less than the lower limit, it may be uneconomical compared to the case where the storage tanks Ts1 to Ts4 are moved and processed.

(Alternative tank)
The alternative tanks Tr1 to Tr4 may be any tank that does not leak contaminated water, but is preferably a welded tank in which a plurality of plate members are joined by welding. Moreover, it is preferable to use a new and empty tank as the alternative tanks Tr1 to Tr4. This welded tank can be manufactured using a general structural rolled steel plate such as SS400, for example, but the inner surface is preferably coated with a resin or the like. In this way, if welded tanks having a relatively long life are used as the alternative tanks Tr1 to Tr4, prevention of leakage of contaminated water is ensured for a long time.

  Further, the volume of the alternative tanks Tr1 to Tr4 is not particularly limited, but is preferably equal to or larger than the volume of the corresponding storage tank Ts1 to Ts4, and is substantially equal to the volume of the corresponding storage tank Ts1 to Ts4. More preferable from the viewpoint. When the volume of the alternative tanks Tr1 to Tr4 is smaller than the volume of the corresponding storage tank Ts1 to Ts4, it is necessary to transfer the contaminated water from any one of the storage tanks Ts1 to Ts4 to the plurality of alternative tanks Tr1 to Tr4. The work may become complicated.

(Contaminated water purification equipment)
As shown in FIG. 2, the contaminated water purification facility U has a plurality of filters 2 and a plurality of adsorbents that selectively adsorb strontium on a stand 1 that has wheels and is capable of self-propelling. An adsorption tower 3 is mounted.

  In this way, the contaminated water purification facility U can be easily and reliably disposed in the vicinity of the storage tank by mounting the plurality of filters 2 and the plurality of adsorption towers 3 on the gantry 1 so as to be movable. The risk of leakage of contaminated water from the contaminated water purification facility U can be reduced.

  The filter 2 is arranged to filter out suspended substances and oil in the contaminated water before the adsorption treatment in the adsorption tower 3. As such a filter, for example, a membrane filter having an average opening diameter of about 0.2 μm is preferably used.

  The plurality of filters 2 are connected in series, and while exchanging contaminated water except for any one, replace the separated filter 2 with a new one, and connect the new filter 2 after the replacement to the most downstream side. It is piped so that it can.

  The plurality of adsorption towers 3 are connected in series like the filter 2, exchanging the separated adsorption towers 3 with new ones while circulating contaminated water excluding any one, and new adsorption after exchange It is piped so that the tower 3 can be connected to the most downstream side.

  As described above, the plurality of filters 2 and the plurality of adsorption towers 3 can be sequentially replaced with new ones, so that the decontamination processing of the storage tanks Ts1 to Ts4 can be performed without delay.

  Since the adsorption tower 3 is filled with an adsorbent that selectively adsorbs strontium, it is treated in the storage tanks Ts1 to Ts4 after being treated by SARRY (Simply Active Water Retrieve and Recovery System) or the like. Strontium, which occupies most of the radioactive material remaining in the stored contaminated water, can be efficiently removed. Thereby, the radioactivity level of storage tank Ts1-Ts4 can be reduced easily.

  Examples of the adsorbent that selectively adsorbs strontium include materials having high adsorption performance for strontium even in the presence of calcium and magnesium, such as A-type zeolite and X-type zeolite.

(pump)
The pump P is not particularly limited as long as it can discharge water in the storage tanks Ts1 to Ts4 and the alternative tanks Tr1 to Tr4. However, the bottoms of the storage tanks Ts1 to Ts4 and the alternative tanks Tr1 to Tr4, that is, plate surfaces A low water level pump that is disposed on the top or on the flange and sucks and sends out surrounding water from the lower part thereof, that is, a submersible pump for low water level drainage is preferably used. Such a low water level pump is suspended by a wire etc. from the upper opening of storage tank Ts1-Ts4 and alternative tank Tr1-Tr4, and is immersed in contaminated water.

  By using the pump P, particularly the low water level pump, the amount of contaminated water inevitably remaining after the contaminated water is discharged from the storage tanks Ts1 to Ts4 and the alternative tanks Tr1 to Tr4 can be reduced, and the storage tanks Ts1 to Ts4. The decontamination efficiency can be improved. After using a pump such as a general pump as the pump P, a low water level pump may be further used.

<Decontamination method for contaminated water storage tank>
In FIG. 3, the procedure of the decontamination processing method of the said contaminated water storage tank is shown. Further, in order to explain the decontamination processing method for the contaminated water storage tank in an easy-to-understand manner, FIG. 4 to FIG.

  The decontamination processing method of the contaminated water storage tank in FIG. 3 includes a first step (step S1) in which the contaminated water is discharged and decontaminated from the first storage tank Ts1 and introduced into the first alternative tank Tr1, and the k th (K is a natural number) This is a step of discharging and purifying contaminated water from the storage tank Tsk and flowing into the k−1th storage tank Ts (k−1), and k is repeatedly performed from 2 to n = 4. A second step (step S2), a third step (step S3) for introducing low-concentration contaminated water in the storage tanks Ts1 to Ts3 after the second step into the alternative tanks Tr2 to Tr4, and a post-second step 1 Alternatively, the low concentration contaminated water in the plurality of storage tanks Ts1 to Ts3 or the water in the one or more alternative tanks Tr1 to Tr4 flows into the n = 4th storage tank Ts4 after the second step, Low concentration contaminated water And a fourth step of introducing (step S4) to one or more alternative tanks Tr1 to Tr4.

<First step>
In the first step of step S1, as shown in FIG. 4, first, the contaminated water is discharged from the first storage tank Ts1 by the pump P and supplied to the contaminated water purification facility U. Then, purified water obtained by purifying the contaminated water by the contaminated water purification facility U is introduced into the first alternative tank Tr1.

  Thereby, the contaminated water is discharged from the first storage tank Ts1, but it is difficult to completely discharge the entire amount of the contaminated water inside the storage tank Ts1. For this reason, in the storage tank Ts1 after discharging the contaminated water, the contaminated water slightly remains at the bottom and the radioactive substance adheres to the inner wall surface.

  The radioactive substance content of the purified water introduced into the alternative tank Tr1 depends on the capability of the contaminated water purification facility U, but is preferably about 100 Bq / cc.

<Second step>
In the second step of step S2, the radioactive material remaining in the storage tank Ts (k-1) from which the contaminated water has been discharged is purified water that has been discharged and purified from the contaminated water stored in the next storage tank Tsk. Dilute. This second step is repeated from k to 2 to n.

  In the first second step, as shown in FIG. 5, first, the contaminated water is discharged from the second storage tank Ts2 by the pump P, and the purified water obtained by purifying the contaminated water in the contaminated water purification facility U is the first. It flows into the storage tank Ts1.

  As a result, the contaminated water remaining in the first storage tank Ts1 is diluted with the purified water that has flowed in, and the radioactive material adhering to the inner wall surface is washed away and dissolved in the purified water. Therefore, the 1st storage tank Ts1 will be in the state which stores the low concentration contaminated water in which the radioactive substance which remained on the bottom part and the inner wall surface was diluted.

  When almost all the contaminated water in the second storage tank Ts2 is purified and flows into the first storage tank Ts1, the radioactive substance content of the low concentration contaminated water in the first storage tank Ts1 is 5,000 Bq / cc. Expected to be about.

  In the next second step, as shown in FIG. 6, the contaminated water is discharged from the third storage tank Ts3 by the pump P, and the purified water purified by the contaminated water purification facility U is used as the second storage tank. It flows into Ts2. Further, the second step, that is, the process of diluting the radioactive material remaining in the storage tank from which the contaminated water has been discharged first with the purified water that has been discharged and purified from the next storage tank is repeated in order. .

  Therefore, when this second step is repeated, a small amount of contaminated water remains in the last storage tank Ts4 (generally the last storage tank) as shown in FIG. Ts3 will be in the state which stores the low concentration contaminated water in which the radioactive substance inside was diluted.

  The inflow of purified water into the storage tanks Ts1 to Ts3 in the second step promotes the effect of washing away radioactive substances adhering to the inner wall surfaces of the storage tanks Ts1 to Ts3, for example, using a spray nozzle or the like. It is preferable that the turbulence is generated inside Ts3. The “turbulent flow” refers to a flow that forms a large vortex in the storage tanks Ts1 to Ts3 in addition to a flow in which purified water is sprayed directly on the inner wall surfaces of the storage tanks Ts1 to Ts3. A turbulent flow including shearing of the purified water on the wall surface, separation, and the like may be generated.

<Third step>
In the third step of step S3, as shown in FIGS. 8 and 9, the low-concentration contaminated water in the storage tanks Ts1 to Ts3 is introduced into the alternative tanks Tr2 to Tr4 using the pump P, that is, transferred. Although a small amount of low-concentration contaminated water remains at the bottom of the storage tanks Ts1 to Ts3, since the low-concentration contaminated water has a low radiation dose, an operator wearing protective clothing can discharge or wipe it off manually.

Thereby, it is considered that the surface contamination density of the inner wall surfaces of the storage tanks Ts1 to Ts3 is reduced to, for example, about 400 Bq / cm ² . At this level of radioactivity, workers wearing protective clothing can perform dismantling work.

<4th process>
In the fourth step of step S4, purified water in the first alternative tank Tr1 or low-concentration contaminated water in the other alternative tanks Tr2 to Tr4 as shown in FIG. It flows into Ts4 and dilutes the remaining radioactive material.

  As a result, the low concentration contaminated water formed in the fourth storage tank Ts4 is at least one of the alternative tanks Tr1 to Tr4, typically the fourth storage tank, as shown in FIG. It is introduced into an alternative tank (first alternative tank Tr1 in FIG. 11) from which purified water or low-concentration contaminated water that has flowed into Ts4 is discharged.

  Thereby, the radioactive substance remaining in the last storage tank Ts4 is also diluted to become low-concentration contaminated water, and the low-concentration contaminated water in the last storage tank Ts4 is discharged, so that the worker wearing protective clothing Can be dismantled.

  Even if the low-concentration contaminated water is formed by diluting the radioactive substance remaining in the other storage tanks Ts1 to Ts3, the radioactive substance remaining in the final storage tank Ts4 is sufficiently radioactive. The substance content is considered low. For this reason, in this 4th process, you may flow the low concentration contaminated water in alternative tank Tr2-Tr4 into storage tank Ts4.

  In the decontamination processing method for the contaminated water storage tank, the contaminated water is discharged from the storage tanks Ts1 to Ts4 by first using a general pump as the pump P so that the contaminated water in the storage tank has a certain level. It is preferable to discharge the contaminated water until it reaches the end, and then further discharge the contaminated water using a low water level pump as the pump P. The polluted water can be discharged up to the certain water level using, for example, a relatively general-purpose and large-capacity pump such as a centrifugal pump as the pump P through a nozzle or the like disposed on the side surface of the storage tank.

<Advantages>
The decontamination method for the contaminated water storage tank purifies the contaminated water discharged from the next k-th storage tank Tsk into the k-1th storage tank Ts (k-1) from which the contaminated water was discharged first. By flowing in the purified water obtained, the radioactive material remaining in the storage tank Ts (k-1) from which the contaminated water has been discharged is diluted. Accordingly, the radioactivity level of the first to (n-1) th storage tanks Ts1 to Ts (n-1) can be reduced relatively easily and inexpensively without increasing the amount of contaminated water using new water. Can do.

[Other Embodiments]
The said embodiment does not limit the structure of this invention. Therefore, in the above-described embodiment, the components of each part of the above-described embodiment can be omitted, replaced, or added based on the description and common general knowledge of the present specification, and they are all interpreted as belonging to the scope of the present invention. Should.

  The alternative tank used for the decontamination method for the contaminated water storage tank does not have to correspond one-to-one with the storage tank. For example, one large alternative tank may correspond to a plurality of storage tanks. In addition, it is possible to equalize the contamination level by transferring the low-concentration contaminated water from each storage tank to a plurality of alternative tanks in the third step. In addition, when the low-concentration contaminated water introduced into the alternative tank is sequentially subjected to further processing steps and finally processed until it can be released to the ocean or the like, the alternative tank may be one having the same size as the storage tank.

  In the decontamination processing method for the contaminated water storage tank, the third step is not essential. In other words, if there is one alternative tank that receives purified water in the first step in order to reduce the contamination level of the storage tank, the contaminated water in the plurality of storage tanks can be diluted into low-concentration contaminated water. . After that, in the unlikely event that it leaks from the storage tank, it becomes easy to manually recover from the pit, and the risk of expanding radioactive contamination can be reduced.

  Moreover, in the decontamination processing method for the contaminated water storage tank, the second step and the third step may be performed in parallel. As a specific example, as shown in FIG. 12, simultaneously with the second step of discharging and purifying contaminated water from the kth storage tank Tsk and flowing into the k−1th storage tank Ts (k−1), k A third step of introducing the low-concentration contaminated water in the second storage tank Ts (k-2) into the alternative tank Tr (k-1) can be performed. Thereby, decontamination of a plurality of storage tanks can be speeded up.

  In the decontamination processing method for the contaminated water storage tank, the fourth step may be performed prior to the third step.

  In the decontamination method for the contaminated water storage tank, the fourth step is not essential. For example, when there is a weld type tank with a small possibility of occurrence of leakage in a plurality of storage tanks, this weld type tank can be left undiluted at the end. Further, when a large number of storage tanks are decontaminated, even if only the contaminated water remaining in the last storage tank is diluted with non-contaminated water, it can be evaluated that the increase in the contaminated water is not large.

  Further, in the second step, the purified water that is introduced to dilute the radioactive material remaining in the storage tank from which the contaminated water has been discharged first is one of the purified water obtained by discharging and purifying from the subsequent storage tank. Part. In other words, in the second step, the radioactive material is diluted to the minimum necessary and the remaining purified water is directly introduced into the alternative tank, so that the purified water flows into the storage tank from which the contaminated water has been discharged and this The time and energy cost for introducing low-concentration contaminated water from the storage tank to the alternative tank can be reduced.

  Moreover, as for the alternative tank used in the decontamination processing method for the contaminated water storage tank, the used tank may be reused, or the free capacity of the tank in which the contaminated water is already stored may be used. . When a used tank is used as an alternative tank, radioactive contamination is caused on the inner wall to such an extent that the contamination level can be sufficiently reduced by introducing purified water purified from the contaminated water in the storage tank or low-concentration contaminated water diluted from the contaminated water in the storage tank. You may use the thing to which the substance adhered or the contaminated water remained in the bottom part. Furthermore, if the alternative tank is a tank with a low risk of leakage, such as a welded tank, high-concentration contaminated water is stored in the alternative tank, and purified water or low-concentration contaminated water is introduced from the storage tank. The later contamination level may be higher than the storage tank.

  Moreover, the contaminated water purification equipment used in the decontamination processing method for the contaminated water storage tank may have a sending unit such as a booster pump, a cushion tank, and a pump for sending purified water from the cushion tank.

  In addition, the contaminated water purification facility is particularly preferable to have one or a plurality of adsorption towers filled with an adsorbent that selectively adsorbs strontium as in the above embodiment, but the radioactivity level can be sufficiently reduced. Any material can be used as long as it can remove radioactive strontium.

  Moreover, the contaminated water purification equipment may have only one or a plurality of adsorption towers.

  Further, the frame of the contaminated water purification facility may have no wheels, and may be movable using, for example, a forklift or a unic car. Further, the contaminated water purification facility may be one that does not have a mount, is disassembled and transported, and is assembled on site.

  The decontamination treatment method for the contaminated water storage tank is widely applicable to decontamination of these storage tanks when there are multiple radioactively contaminated water storage tanks, but is particularly arranged at the accident nuclear power plant. It can utilize suitably in order to process a plurality of storage tanks.

1 stand 2 filter 3 adsorption tower P pump S1 1st process S2 2nd process S3 3rd process S4 4th process Tr1-Tr4 alternative tank Ts1-Ts4 storage tank U contaminated water purification equipment

Claims (7)

A decontamination method for n storage tanks (n is 2 or more) in which contaminated water containing radioactive substances is stored,
A first step of discharging and purifying the contaminated water from the first storage tank and introducing it into an alternative tank;
a second step of discharging and purifying the contaminated water from the kth storage tank and flowing into the k-1th storage tank,
A decontamination treatment method for a contaminated water storage tank, wherein the second step is repeated from k to 2 to n.   The decontamination processing method for a contaminated water storage tank according to claim 1, further comprising a third step of introducing the low-concentration contaminated water in the storage tank after the second step into the alternative tank.   The low concentration contaminated water in the storage tank after the second step or the water in the alternative tank flows into the nth storage tank after the second step, and the diluted low concentration contaminated water is introduced into the alternative tank. The decontamination processing method for a contaminated water storage tank according to claim 1 or 2, further comprising a fourth step.   The method for decontamination of a contaminated water storage tank according to claim 1, wherein the contaminated water is discharged by a pump, and from a predetermined water level by a low water level pump.   The contaminated water storage according to any one of claims 1 to 4, wherein the storage tank has a plurality of members fastened by bolting, and the alternative tank has a plurality of members joined by welding. Decontamination method for tanks.   The contaminated water according to any one of claims 1 to 5, wherein the purification uses one or more adsorption towers mounted on a movable frame and filled with an adsorbent that selectively adsorbs strontium. Decontamination method for storage tanks.   The method for decontamination treatment of a contaminated water storage tank according to any one of claims 1 to 6, wherein the purified water flows into the storage tank so that turbulent flow is generated in the storage tank.

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