JP6585405B2 - Radioactive contamination water storage method and radioactive contamination water storage device - Google Patents

Description

  The present invention relates to a radioactively contaminated water storage method and a radioactively contaminated water storage device.

  Contaminated water containing radioactive pollutants such as radioactive cesium and radioactive strontium, for example, circulating water for core cooling and wastewater at nuclear power plants after the accident, reduce the radioactive pollutants below the standard value to prevent environmental destruction Otherwise, it is not allowed to discharge. For this reason, in the nuclear power plant after the accident, contaminated water obtained by collecting surplus reactor cooling water is stored in many tanks.

  Since these tanks that store contaminated water have a useful life, it is necessary to dismantle tanks near the expiration date. In order to dismantle such a tank, it is necessary to sufficiently reduce the amount of radioactive contaminants contained in the members constituting the tank.

  As a tank for storing such contaminated water, a welding type tank in which a plurality of plate members are joined by welding, or a bolt tightening type tank formed by fastening bolts between flanges arranged on the periphery of the plurality of plate members is used. It is done. As the plate material of such a tank, for example, a general structural rolled steel plate such as SS400 is used. In addition, such a tank for storing contaminated water is generally coated on its inner surface with resin or the like in order to prevent corrosion.

  However, rust occurs when the stored contaminated water comes into contact with the steel constituting the tank due to peeling or damage of the coating on the inner surface of the tank. There is a possibility that radioactive contaminants may be taken into this rust, and when radioactive contaminants are taken into rust, it is necessary to remove the radioactive contaminants from this rust, so decontamination work of steel is required when dismantling the tank It becomes. In order to eliminate such decontamination work, it is desirable to suppress the incorporation of radioactive contaminants into rust. Here, for example, as an apparatus for removing contaminants in the tank, an apparatus for removing contaminants attached to the inner wall surface of the tank while moving along the inner wall surface of the tank has been proposed (Japanese Patent Laid-Open No. 10-2959). reference). However, even if it uses the decontamination apparatus described in this gazette, a radioactive pollutant cannot be removed from the rust currently formed to the inside of steel materials.

Japanese Patent Laid-Open No. 10-2959

  The present invention has been made based on the above-described circumstances, and provides a radioactively contaminated water storage method and a radioactively contaminated water storage device that suppress the incorporation of radioactive strontium into rust generated in a tank that stores radioactively contaminated water. With the goal.

Utilizing the property of adsorbing various ions of iron hydroxide (III), a second hydroxide that coprecipitates the above radionuclide and the like by adsorption onto the iron hydroxide (III) of the radionuclide coexisting in the solution Iron agglomeration methods are known. As a result of analyzing and diligently analyzing the phenomenon in the ferric hydroxide agglomeration method, the present inventors can suppress the incorporation of strontium into rust by setting the pH of the contaminated water stored in the tank to 7 or less. I found. That is, in the ferric hydroxide aggregation method, hydroxoiron (III) ions (Fe (OH) ₂ ⁺ and Fe (H) ₄ ⁻ generated according to the pH of the solution are formed on the surface of the iron (III) hydroxide particles. ) Is adsorbed. When these hydroxoiron (III) ions are adsorbed on the surface of the iron (III) hydroxide particles, an electric double layer is formed, and the surface of the iron (III) hydroxide particles is positively or negatively charged to generate a zeta potential. Since the zeta potential of the iron (III) hydroxide particles becomes a negative value when the pH of the solution exceeds 7, when strontium ions having a positive charge are present in the solution, the strontium is converted into iron hydroxide (III ) Adsorb to particles. This strontium-adsorbed iron hydroxide (III) changes to goethite, which is a kind of rust, by crystallization due to dehydration over time. When this strontium changes to goethite, It is taken into the crystal. From these facts, the present inventors can suppress the adsorption of strontium to iron hydroxide by setting the pH of the contaminated water stored in the tank to 7 or less, and as a result, suppress the incorporation of strontium into rust. I found out that I can do it.

  That is, the invention made to solve the above-mentioned problems is a method for storing radioactive contaminated water in a tank, wherein the pH of the contaminated water stored in the tank is controlled to 7 or less. Contaminated water storage method.

  Since the radioactive contaminated water storage method controls the pH of the radioactive contaminated water stored in the tank to 7 or less, adsorption of strontium to iron hydroxide which is an initial product of rust can be suppressed. As a result, the radioactive contaminated water storage method suppresses the incorporation of strontium into rust such as goethite and magnetite that change from iron hydroxide. As a result, the decontamination work of the steel material at the time of dismantling the tank can be omitted or reduced.

  As the lower limit of the pH control range of the contaminated water, 6 is preferable. Thus, corrosion of tank inner surface etc. can be suppressed by making the pH control range of contaminated water more than the said minimum.

  The pH control may be performed on the contaminated water stored in the tank. Since the contaminated water stored in the tank is basically not transferred until the tank is disassembled, the pH of the contaminated water after the control is controlled by controlling the pH of the contaminated water stored in the tank in this way. Fluctuation can be reduced, and the pH of contaminated water can be easily controlled.

  It is preferable to include a step of storing the radioactive contaminated water in the intermediate tank and a step of transferring the contaminated water stored in the intermediate tank to the tank. pH control may be performed. Thus, by performing pH control on the contaminated water stored in the intermediate tank before being transferred to the tank, the contaminated water after pH control is transferred to the tank. Adsorption of strontium on iron can be more reliably suppressed.

  A step of directly transferring the radioactively contaminated water to the tank may be provided, and the pH control may be performed in a pipe in the direct transfer step. Thus, by performing pH control on the contaminated water in the piping before being transferred to the tank, the contaminated water after pH control is transferred to the tank, so that strontium to iron hydroxide in the tank Can be more reliably suppressed. Further, by directly transferring the contaminated water to the tank, there is no need for a facility for temporarily storing the contaminated water before the transfer to the tank, and the facility for storing the contaminated water can be reduced in size.

  As the pH control, bubbling of carbon dioxide-containing gas may be used. In this way, by performing pH control by bubbling the carbon dioxide-containing gas, the contaminated water can be stirred without using a stirrer, so that the pH of the contaminated water can be easily controlled uniformly in a shorter time.

  Another invention made to solve the above problems is an apparatus for storing radioactive contaminated water in a tank, wherein the tank for storing the contaminated water and the pH of the contaminated water stored in the tank are 7 It is a radioactively contaminated water storage apparatus characterized by including the mechanism controlled below.

  Since the said radioactive contamination water storage apparatus is equipped with the mechanism which controls the pH of the radioactive contamination water stored in a tank to 7 or less, it can suppress adsorption | suction of strontium to the iron hydroxide which is an initial product of rust. As a result, the radioactive polluted water storage device can suppress the uptake of strontium into rust such as goethite or magnetite that changes from iron hydroxide, and can omit or reduce the decontamination work of the steel material when the tank is disassembled.

  As described above, the radioactively contaminated water storage method and the radioactively contaminated water storage device of the present invention can suppress the incorporation of radioactive strontium into rust generated in a tank that stores radioactively contaminated water.

It is a schematic diagram which shows the structure of the radioactive contamination water storage apparatus which concerns on 1st embodiment of this invention. It is a schematic diagram which shows the structure of the radioactive contamination water storage apparatus which concerns on 2nd embodiment of this invention. It is a schematic diagram which shows the structure of the radioactive contamination water storage apparatus which concerns on 3rd embodiment of this invention. It is a graph which shows the pH change of the coprecipitation rate of the zeta potential and ⁹⁰ Sr of an iron (III) hydroxide particle.

  Hereinafter, embodiments of the radioactively contaminated water storage device and the radioactively contaminated water storage method according to the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
The radioactive contaminated water storage apparatus shown in FIG. 1 is an apparatus that stores radioactive contaminated water C in a tank 1. The radioactive contaminated water storage device mainly includes a tank 1 for storing the contaminated water C and a pH control mechanism 2 for controlling the pH of the contaminated water C stored in the tank 1 to 7 or less.

<Tank>
The tank 1 for storing the radioactive contaminated water C is not particularly limited, but is used for storing contaminated water containing radioactive substances in the nuclear power plant after the accident. A bolt-clamped tank formed by fastening at a position is assumed.

  Although it does not specifically limit as a minimum of the average internal diameter of the tank 1, 3 m is preferable and 5 m is more preferable. On the other hand, the upper limit of the average inner diameter of the tank 1 is preferably 25 m, and more preferably 20 m. Since the height of the tank 1 is limited due to the drainage capacity of the discharge pump used when discharging contaminated water from the tank 1, the tank capacity cannot be increased beyond a predetermined level unless the average inner diameter of the tank 1 is less than the above lower limit. There is a possibility that the number of tanks 1 for storing the contaminated water C increases. Conversely, if the average inner diameter of the tank 1 exceeds the above upper limit, the time until the pH of the contaminated water C in the tank 1 becomes uniform during pH adjustment becomes longer, and the time until pH confirmation after pH adjustment becomes longer. There is a fear. The “average inner diameter” means an average value of the minimum horizontal dimension inside the tank and the horizontal dimension orthogonal thereto.

  Moreover, as a minimum of the average height of the tank 1, 3 m is preferable and 5 m is more preferable. On the other hand, the upper limit of the average height of the tank 1 is preferably 25 m, and more preferably 20 m. If the average height of the tank 1 is less than the above lower limit, the installation area of the tank 1 is increased with respect to the capacity for storing the contaminated water C, so that the storage efficiency with respect to the installation area may be reduced. Further, since the state of the contaminated water C in the tank 1 is checked from the manhole at the top of the tank 1, if the average height of the tank 1 exceeds the upper limit, it is difficult to check the state of the contaminated water C in the tank 1. There is a risk.

  In addition, the contaminated water C stored in the tank 1 is typically contaminated water containing radioactive materials such as core cooling circulating water and waste water in a nuclear power plant after an accident, especially radioactive strontium. It is made with water.

  Although it does not specifically limit as a pollutant density | concentration of the contaminated water C stored in the tank 1, For example, you may be 500 Bq / cc or more and 500,000 Bq / cc or less.

  The contaminated water C stored in the tank 1 is supplied into the tank 1 through a contaminated water supply pipe (not shown). The contaminated water supply pipe is inserted from, for example, a manhole at the top of the tank 1 to supply the contaminated water C into the tank 1.

<PH control mechanism>
The pH control mechanism 2 includes a pH sensor 3, a pH adjuster supply device 4, and a pH adjuster supply pipe 5 as shown in FIG.

(PH sensor)
The pH sensor 3 measures the pH of the contaminated water C in the tank 1. The pH sensor 3 is suspended from, for example, a manhole at the top of the tank 1 and is disposed in the contaminated water C in the tank 1.

  As the pH sensor 3, a semiconductor type pH sensor such as an ISFET (Ion Sensitive Field Effect Transistor), a glass electrode type pH sensor, or the like can be used.

(PH adjuster supply device)
The pH adjuster supply device 4 discharges the pH adjuster from the discharge port.

(PH adjuster supply pipe)
One end of the pH adjusting agent supply pipe 5 is connected to the outlet of the pH adjusting agent supply device 4, and the other end is disposed in the contaminated water C in the tank 1. The pH adjuster discharged from the pH adjuster supply device 4 is introduced into the contaminated water C through the pH adjuster supply pipe 5.

  The pH control mechanism 2 first measures the pH of the contaminated water C in the tank 1 with the pH sensor 3, and controls the pH of the contaminated water C stored in the tank 1 according to the measurement result. Specifically, the pH control mechanism 2 is stored in the tank 1 by the pH adjuster supply device 4 and the pH adjuster supply pipe 5 when the pH of the contaminated water C stored in the tank 1 exceeds 7. A pH adjuster is introduced into the contaminated water C, and the pH of the contaminated water C is adjusted to 7 or less. When the pH of the contaminated water C stored in the tank 1 is 7 or less, the pH control mechanism 2 does not input the pH adjuster through the pH adjuster supply device 4 and the pH adjuster supply pipe 5. In this way, the pH control mechanism 2 controls the pH of the contaminated water C stored in the tank 1 to 7 or less. In addition, when introducing a pH adjuster, the pH control mechanism 2 uses, for example, the pH of the contaminated water C measured by the pH sensor 3 and the stored amount of the contaminated water C in order to lower the pH of the contaminated water C to 7 or less. A required amount of the pH adjusting agent is introduced into the contaminated water C through the pH adjusting agent supply device 4 and the pH adjusting agent supply pipe 5.

  As a minimum of pH of contaminated water C in tank 1 after pH control, 6 is preferred and 6.5 is more preferred. On the other hand, the upper limit of the pH of the contaminated water C in the tank 1 after pH control is 7. Corrosion of the inner surface of the tank 1 is greatly affected by the oxidation-reduction potential, temperature, etc. If the pH of the contaminated water C in the tank 1 is less than the lower limit, the corrosion of the inner surface of the tank 1 may be accelerated. . In addition, if the pH of the contaminated water C in the tank 1 is less than the lower limit, the amount of pH adjuster added increases, and the processing cost for pH control may be excessive. In addition, even if the pH of the contaminated water C is less than the above lower limit, the effect of suppressing adsorption of strontium to iron hydroxide can be obtained, but when the pH of the contaminated water C is 4 or less, the generation of rust is promoted. On the other hand, if the pH of the contaminated water C in the tank 1 exceeds the above upper limit, strontium is adsorbed on the surface of the iron hydroxide particles, and there is a possibility that strontium uptake into rust cannot be sufficiently suppressed.

  As a pH adjuster for adjusting the pH of the contaminated water C to 7 or less, any of solid, liquid, and gas can be used. Among these, in consideration of dissolution and diffusibility in the contaminated water C, liquid and gas are preferable.

  Examples of the liquid pH adjuster include carbonic acid, sulfuric acid, hydrochloric acid and the like. Among these, those having no corrosiveness to the anion, that is, carbonic acid and sulfuric acid are preferable in that corrosion hardly occurs.

  As the gaseous pH adjuster, a carbon dioxide-containing gas is preferable in terms of easy availability and easy handling at room temperature. Moreover, when using such a pH adjuster of gas, it is preferable to bubble gas and introduce | transduce into the contaminated water C. FIG. For example, by inserting a pipe into the contaminated water C and flowing a gas at an appropriate flow rate into the pipe, the gas can be bubbled in the contaminated water C by discharging the gas from the tip of the pipe. By using gas bubbling in this way, the contaminated water C can be stirred without using a stirrer. As a result, the pH adjuster of the introduced gas is easily dissolved in the contaminated water C, and the pH of the contaminated water C can be adjusted to be uniform in a shorter time. Therefore, it is preferable to adjust the pH of the contaminated water C using bubbling of carbon dioxide-containing gas.

  As described above, since the radioactive contaminated water storage device controls the pH of the contaminated water C stored in the tank 1 to 7 or less by the pH control mechanism 2, adsorption of strontium to iron hydroxide can be suppressed. As a result, the radioactive contaminated water storage device can suppress the uptake of radioactive strontium into the rust generated in the tank 1.

[Radio-polluted water storage method]
Then, the radioactive contaminated water storage method which concerns on 1st embodiment of this invention performed in the radioactive contaminated water storage apparatus of FIG. 1 is demonstrated.

  The radioactive contaminated water storage method is a method of storing the radioactive contaminated water C in the tank 1. In the radioactive contaminated water storage method, the pH of the contaminated water C stored in the tank 1 is controlled to 7 or less. That is, the radioactive contaminated water storage method includes a step (pH control step) of controlling the pH of the contaminated water C stored in the tank 1 to 7 or less.

<PH control step>
The pH control step includes a step of measuring the pH of the contaminated water C stored in the tank 1 (pH measuring step) and a step of adjusting the pH of the contaminated water C stored in the tank 1 (pH adjusting step). And have.

(PH measurement process)
In the pH measurement step, the pH of the contaminated water C stored in the tank 1 is measured by the pH sensor 3.

(PH adjustment step)
In the pH adjustment step, the pH of the contaminated water C in the tank 1 is adjusted by the pH control mechanism 2 based on the pH of the contaminated water C in the tank 1 measured in the pH measurement step.

  After controlling the pH of the contaminated water C in the tank 1 by the pH control step, the tank 1 is substantially sealed. Thereafter, since the contaminated water C is stored in a substantially sealed state until the tank 1 is dismantled, the pH of the contaminated water C in the tank 1 hardly changes and a pH of 7 or less is maintained.

  Further, the contaminated water C stored in the tank 1 is basically stored in the tank 1 without being transferred until the tank 1 is disassembled. Since the radioactive contaminated water storage method performs pH control on the contaminated water C stored in the tank 1 in this manner, the variation in the pH of the contaminated water after the control can be reduced, and the pH of the contaminated water is controlled. Easy to do.

  Further, in order to suppress the incorporation of radioactive strontium into rust more reliably, before the adsorption of strontium to iron hydroxide proceeds, that is, after the storage of the contaminated water C in the tank 1, a relatively early time. It is preferable to carry out the pH adjustment step. On the other hand, even after the adsorption of strontium to iron hydroxide proceeds to some extent, the elution of strontium ions and the dissolution of iron hydroxide can be advanced by adjusting the pH of the contaminated water C to 7 or less. Therefore, even when strontium is adsorbed on iron hydroxide, the effect of suppressing the incorporation of radioactive strontium into the rust generated in the tank 1 can be obtained by performing the pH adjustment step.

[Second Embodiment]
The radioactive contaminated water storage apparatus shown in FIG. 2 is an apparatus for storing radioactive contaminated water C in the tank 1. The radioactive contaminated water storage device has a tank 1 for storing the contaminated water C, an intermediate tank 11 for temporarily storing the contaminated water C to be transferred to the tank 1, and a pH of the contaminated water C stored in the intermediate tank 11. PH control mechanism 12 which controls to 7 or less, and the contaminated water supply piping 13 and the supply pump 14 which transfer the contaminated water C stored in the intermediate tank 11 to the tank 1 are mainly provided.

<Intermediate tank>
The intermediate tank 11 is a tank that temporarily stores the contaminated water C stored in the tank 1 before transferring it to the tank 1. In the radioactive contaminated water storage device, the pH of the contaminated water C temporarily stored in the intermediate tank 11 is controlled. As the intermediate tank 11, for example, one having the same structure as the tank 1 can be used. That is, it is possible to use a bolted tank formed by fastening bolts between flanges disposed on the peripheral edges of a plurality of plate members.

  The lower limit of the ratio of the capacity of the intermediate tank 11 to the capacity of the tank 1 is preferably 1/20, and more preferably 1/10. On the other hand, the upper limit of the capacity ratio is preferably 6/5, and more preferably 1. If the capacity ratio is less than the lower limit, the amount of pH controllable in the intermediate tank 11 is too small relative to the amount of contaminated water C stored in the tank 1, so that the pH control of the contaminated water C stored in the tank 1 is controlled. There is a possibility that the time required for the process becomes too long. On the contrary, if the ratio of the capacities exceeds the upper limit, the capacity of the intermediate tank 11 is larger than necessary than the capacity of the tank 1, and the intermediate tank 11 may become unnecessarily large.

  Although it does not specifically limit as a minimum of the average internal diameter of the intermediate tank 11, 3 m is preferable and 5 m is more preferable. On the other hand, the upper limit of the average inner diameter of the intermediate tank 11 is preferably 25 m, and more preferably 20 m. Since the height of the intermediate tank 11 is limited due to the transfer capability of the supply pump 14 used when contaminated water is transferred from the intermediate tank 11, if the average inner diameter of the intermediate tank 11 does not satisfy the above lower limit, the capacity of the tank 11 is increased. There is a possibility that the number of times of transfer of the contaminated water C to the tank 1 may increase because it cannot be made larger than a predetermined value. Conversely, if the average inner diameter of the intermediate tank 11 exceeds the above upper limit, the time until the pH of the contaminated water C in the intermediate tank 11 becomes uniform during pH adjustment becomes longer, and the time until pH confirmation after pH adjustment is increased. May be longer.

  Moreover, as a minimum of the average height of the intermediate tank 11, 3 m is preferable and 5 m is more preferable. On the other hand, the upper limit of the average height of the intermediate tank 11 is preferably 25 m, and more preferably 20 m. If the average height of the intermediate tank 11 is less than the above lower limit, the installation area of the intermediate tank 11 increases with respect to the amount of contaminated water C that can be stored, so that the capacity efficiency of pH control per installation area decreases. There is a fear. In addition, since the pH adjusting agent is introduced into the intermediate tank 11 from the manhole at the top of the intermediate tank 11, when the average height of the intermediate tank 11 exceeds the above upper limit, the pH adjusting agent is introduced into the intermediate tank 11. It may be difficult to remove.

  The contaminated water C stored in the intermediate tank 11 is supplied into the intermediate tank 11 through a pipe different from the contaminated water supply pipe 13 (not shown). This pipe is inserted from, for example, a manhole at the upper part of the intermediate tank 11 to supply the contaminated water C into the intermediate tank 11.

<PH control mechanism>
The pH control mechanism 12 includes a pH sensor 15, a pH adjusting agent supply device 16, and a pH adjusting agent supply pipe 17, as shown in FIG. The pH sensor 15, the pH adjuster supply device 16, and the pH adjuster supply tube 17 have the same functions as the pH sensor 3, the pH adjuster supply device 4, and the pH adjuster supply tube 5 of the first embodiment, for example. Things can be used. Since these members constituting the pH control mechanism 12 are installed in the intermediate tank 11 different from the tank 1 of the first embodiment, the same members as those constituting the pH control mechanism 2 may not always be used. However, since it has the same function, description of these members is abbreviate | omitted.

  The lower limit of the pH of the contaminated water C in the intermediate tank 11 after pH control is preferably 6, and more preferably 6.5. On the other hand, the upper limit of the pH of the contaminated water C in the intermediate tank 11 after pH control is 7. Corrosion of the inner surface of the tank 1 is greatly affected by the oxidation-reduction potential, temperature, etc. If the pH of the contaminated water C in the intermediate tank 11 is less than the lower limit, the corrosion of the inner surface of the tank 1 after the transfer of the contaminated water C, etc. Corrosion may be accelerated. Moreover, if the pH of the contaminated water C in the intermediate tank 11 is less than the above lower limit, the amount of pH adjuster added increases, and the processing cost for pH control may become excessive. On the contrary, if the pH of the contaminated water C in the intermediate tank 11 exceeds the upper limit, the contaminated water C is transferred to the tank 1 and then strontium is adsorbed on the surface of the iron hydroxide particles in the tank 1 to cause rust. The strontium uptake may not be sufficiently suppressed.

<Contaminated water supply piping and supply pump>
The contaminated water supply pipe 13 has one end disposed in the intermediate tank 11 and the other end disposed in the tank 1. A supply pump 14 is disposed in the middle of the contaminated water supply pipe 13. The contaminated water supply pipe 13 and the supply pump 14 transfer the pH-contaminated contaminated water C stored in the intermediate tank 11 into the tank 1. Thereby, the pH of the contaminated water C stored in the tank 1 is controlled to 7 or less.

  The specifications such as the discharge pressure and discharge water amount of the supply pump 14 take into account the pressure loss in the contaminated water supply pipe 13 and the water head up to the installation height of the tank 1 so that the necessary water supply pressure and water supply amount for the tank 1 can be obtained. To be selected.

  Thus, since the radioactive contaminated water storage apparatus controls the pH of the contaminated water C stored in the intermediate tank 11 before being transferred to the tank 1 by the pH control mechanism 12 to 7 or less, the contaminated water C is stored in the tank. Immediately after being transferred to 1, the adsorption of strontium to iron hydroxide can be suppressed. As a result, the radioactive contaminated water storage device can more reliably suppress the uptake of radioactive strontium into the rust generated in the tank 1.

[Radio-polluted water storage method]
Then, the radioactive contaminated water storage method which concerns on 2nd embodiment of this invention performed in the radioactive contaminated water storage apparatus of FIG. 2 is demonstrated.

  In the radioactive contaminated water storage method, the contaminated water stored in the tank 1 is controlled by performing pH control on the contaminated water C stored in the intermediate tank 11 that temporarily stores the contaminated water C transferred to the tank 1. The pH of C is controlled to 7 or less.

  Specifically, the radioactive contaminated water storage method includes a step of storing radioactive contaminated water C in the intermediate tank 11 (intermediate tank storage step) and a pH of 7 or less with respect to the contaminated water C stored in the intermediate tank 11. And a step of transferring the contaminated water C stored in the intermediate tank 11 to the tank 1 (contaminated water transfer step).

<Intermediate tank storage process>
In the intermediate tank storage step, the contaminated water C before being transferred to the tank 1 is stored in the intermediate tank 11. The contaminated water C is supplied into the tank 11 through a pipe different from the contaminated water supply pipe 13 (not shown).

<PH control step>
The pH control step includes a step of measuring the pH of the contaminated water C stored in the intermediate tank 11 (pH measurement step), and a step of adjusting the pH of the contaminated water C stored in the intermediate tank 11 (pH adjustment). Process).

(PH measurement process)
In the pH measurement step, the pH of the contaminated water C stored in the intermediate tank 11 is measured by the pH sensor 15.

(PH adjustment step)
In the pH adjustment step, the pH of the contaminated water C in the intermediate tank 11 is adjusted by the pH control mechanism 12 based on the pH of the contaminated water C in the intermediate tank 11 measured in the pH measurement step.

<Contaminated water transfer process>
In the contaminated water transfer step, the contaminated water C in the intermediate tank 11 whose pH is controlled to 7 or less in the pH control step is transferred to the tank 1. Specifically, the supply pump 14 transfers the contaminated water C in the intermediate tank 11 into the tank 1 through the contaminated water supply pipe 13. Thereby, the pH of the contaminated water C stored in the tank 1 is controlled to 7 or less. Further, in the contaminated water transfer step, after the supply pump 14 transfers the contaminated water C into the tank 1, the tank 1 is substantially sealed. Thereafter, the contaminated water C is stored in the tank 1 until the tank 1 is dismantled.

  In addition, the said intermediate tank storage process, pH control process, and contaminated water transfer process may be performed by a batch process, and may be performed by a continuous process. When these three steps are performed in a continuous process, for example, the supply amount of the contaminated water C to the intermediate tank 11 and the pH adjuster so that the pH of the contaminated water C being transferred in the contaminated water supply pipe 13 is 7 or less. And the transfer amount of the contaminated water C by the supply pump 14 are adjusted.

  Further, for example, the intermediate tank storage step may be performed by batch processing, and the pH control step and the contaminated water transfer step may be performed by continuous processing after the intermediate tank storage step. In this case, since the pH of the contaminated water C transferred to the tank 1 becomes lower as the contaminated water C transferred later, for example, the pH of the contaminated water C after being stored in the tank 1 is 7 or less. The input amount of the pH adjusting agent and the transfer amount of the contaminated water C by the supply pump 14 are adjusted.

  Further, for example, after the intermediate tank storage step and the pH control step are performed by continuous processing, the contaminated water transfer step may be performed by batch processing. In this case, for example, the supply amount of the contaminated water C to the intermediate tank 11 and the input amount of the pH adjuster are adjusted so that the pH of the contaminated water C in the intermediate tank 11 before the transfer to the tank 1 is 7 or less. .

  Thus, since the radioactive contaminated water storage method controls the pH of the contaminated water C stored in the intermediate tank 11 before being transferred to the tank 1 to 7 or less, the contaminated water C is transferred to the tank 1. Immediately thereafter, adsorption of strontium to iron hydroxide can be suppressed. As a result, the radioactive contaminated water storage method can more reliably suppress the adsorption of strontium to iron hydroxide in the tank 1.

[Third embodiment]
The radioactive contaminated water storage apparatus shown in FIG. 3 is an apparatus that stores radioactive contaminated water C in the tank 1. The radioactive contaminated water storage device controls the pH of the contaminated water C to 7 or less in the tank 1 that stores the contaminated water C and the contaminated water supply pipe 25 that directly transfers the contaminated water C to the tank 1. The mechanism 22 is mainly provided.

<PH control mechanism>
The pH control mechanism 22 includes a pH adjuster supply device 23, a pH adjuster supply pipe 24, a contaminated water supply pipe 25, and a pH sensor 26 as shown in FIG. In addition, as the pH adjuster supply apparatus 23, what has the function similar to the pH adjuster supply apparatus 4 of 1st embodiment, for example can be used. Since this pH adjuster supply device 23 is different from the first embodiment in that the pH adjuster is supplied into the contaminated water supply pipe 25, the same pH adjuster supply device 4 as the pH adjuster supply device 4 cannot always be used. However, since it has the same function, description of the pH adjuster supply apparatus 23 is abbreviate | omitted.

(Contaminated water supply piping)
The contaminated water supply pipe 25 is a pipe for directly transferring the contaminated water C such as the core cooling circulating water and waste water in the nuclear power plant after the accident to the tank 1.

(PH adjuster supply pipe)
One end of the pH adjuster supply pipe 24 is connected to the discharge port of the pH adjuster supply apparatus 23, and the other end is connected in the middle of the contaminated water supply pipe 25. Through this pH adjuster supply pipe 24, the pH adjuster discharged from the pH adjuster supply device 23 is introduced into the contaminated water C being transferred through the contaminated water supply pipe 25.

(PH sensor)
The pH sensor 26 measures the pH of the contaminated water C during or before being transferred through the contaminated water supply pipe 25. The pH sensor 26 is disposed on the lower side in the contaminated water supply pipe 25 so as to come into contact with the contaminated water C being transferred in the contaminated water supply pipe 25, for example. Since the pH of the contaminated water C being transferred through the contaminated water supply pipe 25 only needs to be known, the pH sensor 26 determines the pH of the contaminated water C such as circulating water for core cooling and waste water at the nuclear power plant after the accident. You may arrange | position in the location which measures directly.

  As said pH sensor 26, the thing similar to the pH sensor 3 of 1st embodiment can be used, for example.

  The pH control mechanism 22 first measures the pH of the contaminated water supply pipe 25 during or before being transferred through the contaminated water supply pipe 25 by the pH sensor 26, and is transferring the inside of the contaminated water supply pipe 25 according to the measurement result. The pH of the contaminated water C is controlled. Specifically, the pH control mechanism 22 supplies the pH adjuster into the contaminated water C in the contaminated water supply pipe 25 by the pH adjuster supply device 23 and the pH adjuster supply pipe 24, The pH of the contaminated water C being transferred is adjusted to 7 or lower. In addition, when the pH of the contaminated water C is 7 or less during or before being transferred through the contaminated water supply pipe 25, the pH control mechanism 22 uses the pH adjuster supply device 23 and the pH adjuster supply pipe 24 to adjust the pH adjuster. Do not throw in. In this way, the pH control mechanism 22 controls the pH of the contaminated water C being transferred through the contaminated water supply pipe 25 to 7 or less.

  The lower limit of the pH of the contaminated water C being transferred through the contaminated water supply pipe 25 after pH control is preferably 6, and more preferably 6.5. On the other hand, the upper limit of the pH of the contaminated water C after pH control is 7. Corrosion of the inner surface of the tank 1 is greatly affected by the oxidation-reduction potential, temperature, etc. If the contaminated water C during transfer after pH control does not satisfy the above lower limit, the corrosion of the inner surface of the tank 1 may be accelerated. There is. Moreover, if the contaminated water C during the transfer after the pH control is less than the lower limit, the amount of the pH adjuster added increases and the treatment cost for the pH control may be excessive. Conversely, if the contaminated water C after pH control exceeds the upper limit, the contaminated water C is transferred to the tank 1 and then strontium is adsorbed on the surface of the iron hydroxide particles in the tank 1, and strontium to rust. May not be sufficiently suppressed.

  As the pH adjuster for adjusting the pH of the contaminated water C being transferred to 7 or less in the contaminated water supply pipe 25, the same pH adjuster as that used in the radioactive contaminated water storage device of the first embodiment can be used. .

  Alternatively, this gas may be bubbled and introduced into the contaminated water C using a gaseous pH adjuster. For example, the contaminated water C in the contaminated water supply pipe 25 is discharged by discharging the pH adjuster from the other end of the pH adjuster supply pipe 24 by discharging the gaseous pH adjuster from the pH adjuster supply apparatus 23 at an appropriate flow rate. Gas can be bubbled inside. By using gas bubbling in this way, the pH adjusting agent is dissolved in the contaminated water C being transferred through the contaminated water supply pipe 25, and the pH-adjusted contaminated water C is stored in the tank 1.

  Thus, since the radioactive contaminated water storage device controls the pH of the contaminated water C to 7 or less before being transferred to the tank 1 by the pH control mechanism 22, immediately after the contaminated water C is transferred to the tank 1. The adsorption of strontium onto iron hydroxide can be suppressed. As a result, the radioactive contaminated water storage device can more reliably suppress the uptake of radioactive strontium into the rust generated in the tank 1.

[Radio-polluted water storage method]
Then, the radioactive contaminated water storage method which concerns on 3rd embodiment of this invention performed in the radioactive contaminated water storage apparatus of FIG. 3 is demonstrated.

  In the radioactive contaminated water storage method, the pH of the contaminated water C is controlled in the contaminated water supply pipe 25 that directly transfers the contaminated water C to the tank 1, so that the contaminated water C stored in the tank 1 is stored. The pH is controlled to 7 or less.

  Specifically, the radioactive contaminated water storage method includes the step of directly transferring the radioactive contaminated water C to the tank 1 (direct transfer step), and the contaminated water transferred in the contaminated water supply pipe 25 in the direct transfer step. A step of performing pH control on C (pH control step).

<Direct transfer process>
In the direct transfer step, the contaminated water supply pipe 25 directly transfers the contaminated water C to the tank 1. Thus, in the radioactive contaminated water storage method, the contaminated water C stored in the tank 1 is not temporarily stored in the intermediate tank or the like.

<PH control step>
The pH control step includes a step (pH measurement step) of measuring the pH of the contaminated water C during or before transfer in the contaminated water supply pipe 25 and a pH of the contaminated water C being transferred through the contaminated water supply pipe 25. A step of adjusting (pH adjustment step).

(PH measurement process)
In the pH measurement step, the pH of the contaminated water C transferred through the contaminated water supply pipe 25 is measured by the pH sensor 26.

(PH adjustment step)
In the pH adjustment step, the inside of the contaminated water supply pipe 25 is being transferred by the pH control mechanism 22 based on the pH of the contaminated water C being transferred in the contaminated water supply pipe 25 measured in the pH measurement step or before the transfer. The pH of the contaminated water C is adjusted.

  In this way, the radioactive contaminated water storage method transfers the contaminated water C after controlling the pH in the contaminated water supply pipe 25 to the tank 1, so that the hydroxylated water immediately after the contaminated water C is transferred to the tank 1. A state where adsorption of strontium to iron is suppressed can be achieved. As a result, the radioactive contaminated water storage method can more reliably suppress the adsorption of strontium to iron hydroxide in the tank 1. Moreover, since the radioactive contaminated water storage method does not require a facility for temporarily storing the contaminated water C before being transferred to the tank 1, the facility for storing the contaminated water C can be downsized.

[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.

  For example, in the above-described embodiment, an amount of the pH adjusting agent determined from the pH of the contaminated water before pH adjustment is introduced into the contaminated water. However, instead of introducing the pH adjusting agent in the amount obtained in advance as described above, the radioactively contaminated water storage device measures the pH of the contaminated water after pH adjustment while introducing the pH adjusting agent, and the contaminated water is determined to be predetermined. When the pH is lowered to the pH, the charging of the pH adjusting agent may be stopped. In this way, by controlling the input of the pH adjusting agent according to the pH of the contaminated water after the pH adjustment, the pH of the contaminated water can be easily controlled to be in a desired range. In the radioactively contaminated water storage device of the first embodiment and the second embodiment, a pH sensor for measuring the pH of contaminated water before pH control may be used for measuring the pH of contaminated water after pH adjustment.

  In the above embodiment, the pH of the contaminated water before pH adjustment is measured by the pH sensor, but the pH of the contaminated water before pH adjustment may be obtained by other methods. For example, when the pH of the contaminated water can be predicted because the ratio of seawater contained in the contaminated water is known, the predicted pH of the contaminated water may be used. Specifically, the amount of the pH adjuster necessary for adjusting the pH of the contaminated water based on the predicted pH of the contaminated water is obtained. In this case, since it is not necessary to measure the pH of the contaminated water, the pH sensor can be omitted.

  In the second embodiment and the third embodiment, the pH of the contaminated water before being transferred to a tank for storing the contaminated water (hereinafter referred to as a contaminated water storage tank) is controlled. The pH of the contaminated water may be controlled by transferring the contaminated water stored in the contaminated water storage tank to the intermediate tank. For example, when the pH of the contaminated water stored in the contaminated water storage tank exceeds 7, the contaminated water may be transferred to the intermediate tank, and the pH of the contaminated water transferred into the intermediate tank may be adjusted to 7 or less. . Also, for example, in the piping when transferring to the intermediate tank or the piping when transferring the contaminated water once transferred to the intermediate tank to the contaminated water storage tank, the pH of the contaminated water being transferred is adjusted to 7 or less. Also good. By transferring the contaminated water whose pH has been adjusted in this way from the intermediate tank to the contaminated water storage tank, the pH of the contaminated water stored in the contaminated water storage tank can be controlled to 7 or less. By doing so, for example, the pH of the contaminated water stored in the contaminated water storage tank before the installation of the intermediate tank can be controlled to 7 or less, and radioactive strontium to rust generated in the contaminated water storage tank Can be suppressed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

<Consideration of interaction between iron hydroxide and strontium ions>
It is considered that iron hydroxide adheres as a corrosion product in the undercoat corrosion such as the corroded portion of the tank inner surface. The interaction between iron hydroxide and strontium ions was considered.

Utilizing the property of adsorbing various ions of iron hydroxide (III), a second hydroxide that coprecipitates the above radionuclide and the like by adsorption onto the iron hydroxide (III) of the radionuclide coexisting in the solution Iron agglomeration methods are known. In this ferric hydroxide aggregation method, hydroxo iron (III) ions (Fe (OH) ₂ ⁺ and Fe (H) ₄ ⁻ ) generated according to the pH of the solution are formed on the surface of the iron (III) hydroxide particles. Adsorbs. When these hydroxoiron (III) ions are adsorbed on the surface of the iron (III) hydroxide particles, an electric double layer is formed, and the surface of the iron (III) hydroxide particles is positively or negatively charged to generate a zeta potential. When iron (III) hydroxide particles are negatively charged, if strontium ions with a positive charge coexist in the solution, they will attract each other due to the positive and negative charges, and strontium ions will be adsorbed on the iron (III) hydroxide particles. And co-precipitate.

Also, “Junichiro Kimura, Tenson Tsutsui,“ Treatment of radioactive wastewater by coagulation sedimentation (I) ”, Health Physics, 11, 13-19 (1976), p. 13-19 ", it is reported that there is a relationship between the zeta potential of iron (III) hydroxide particles and the coprecipitation rate of ⁹⁰ Sr and pH as shown in FIG. In the region where the pH is about 7 or more, the zeta potential on the surface of the iron (III) hydroxide particles shows a negative value, so that the iron (III) hydroxide particles attract the positive charge of the strontium ions, and ⁹⁰ Sr (III) Coprecipitate with particles. On the other hand, as shown in FIG. 4, the coprecipitation rate is close to 0 when the pH is about 7 or less. Therefore, it is considered that strontium hardly adsorbs to iron hydroxide at a pH of about 7 or less.

On the other hand, in the undercoat corrosion, the cathode part has a higher pH than the anode part, and iron ions eluted at the anode part come into contact with the high pH of the cathode part, and iron (III) hydroxide, which is a corrosion product, is produced. . Since the pH at this time is about 7 to 8.2, it is estimated that ⁹⁰ Sr is adsorbed on iron (III) hydroxide and coprecipitated. From FIG. 4, it is considered that a maximum of about 20% of strontium may co-precipitate with corrosion products, that is, adsorb to iron (III) hydroxide at a pH of 7 to 8.2. From these facts, the present inventors can suppress the adsorption of strontium to iron hydroxide by setting the pH of the contaminated water stored in the tank to 7 or less, and consequently suppress the incorporation of strontium into rust. I found out that I can do it.

  Since the radioactive contaminated water storage method and the radioactive contaminated water storage device of the present invention can suppress the uptake of radioactive strontium into rust generated in the tank that stores the radioactive contaminated water, the contaminated water generated particularly in the nuclear power plant after the accident is collected. It can utilize suitably for the contaminated water tank arrange | positioned for the purpose of storing.

DESCRIPTION OF SYMBOLS 1 Tank 2, 12, 22 pH control mechanism 3, 15, 26 pH sensor 4, 16, 23 pH regulator supply apparatus 5, 17, 24 pH regulator supply pipe 11 Intermediate tank 13, 25 Contaminated water supply piping 14 Supply pump C Contaminated water

Claims (6)

A method for storing radioactively contaminated water containing radioactive strontium in a tank,
By controlling the pH of the contaminated water stored in the tank 7 below, to suppress the adsorption of the radioactive strontium into iron (III) hydroxide which is the initial product of rust caused to the tank Radioactive contaminated water storage method characterized.   The radioactive contaminated water storage method according to claim 1, wherein the lower limit of the pH control range of the contaminated water is 6 or more. Storing the radioactively contaminated water in an intermediate tank;
A step of transferring the contaminated water stored in the intermediate tank to the tank,
The radioactively contaminated water storage method according to claim 1 or 2, wherein the pH control is performed on the contaminated water stored in the intermediate tank. A step of directly transferring the radioactively contaminated water to the tank;
The radioactively contaminated water storage method according to claim 1 or 2, wherein the pH control is performed in a pipe in the direct transfer step. The radioactive polluted water storage method according to any one of claims 1 to 4 , wherein bubbling of a carbon dioxide-containing gas is used as the pH control. A device for storing radioactively contaminated water containing radioactive strontium in a tank,
A tank for storing the contaminated water;
A mechanism for suppressing adsorption of the radioactive strontium to iron (III) hydroxide, which is an initial product of rust generated in the tank, by controlling the pH of the contaminated water stored in the tank to 7 or less. A radioactively contaminated water storage device comprising:

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