JP6427012B2 - Tank decontamination method - Google Patents

Description

  The present invention relates to a tank decontamination method.

  Contaminated water containing radioactive substances such as radioactive cesium and radioactive strontium, such as drainage water, circulating water for core cooling after a nuclear accident, etc. can not be discharged unless the radioactive substances are removed to prevent environmental destruction. . For this reason, the contaminated water which collect | recovered the cooling water etc. of the reactor which became surplus after the nuclear accident is stored by many tanks.

  As the tanks for storing these contaminated water have a lifetime, tanks near the expiration date need to be dismantled and disposed of one by one. In order to disassemble the tank storing the contaminated water, it is necessary to sufficiently reduce the amount of contaminants in the tank.

  However, the tanks that are often used after the nuclear accident are not designed to discharge all the stored liquid, and a certain amount of contaminated water remains even after the contaminated water is discharged from the nozzle provided at the bottom. Do. Many of the tanks used after the nuclear accident have a capacity of around 1000 kL, and the amount of water remaining after discharging from the nozzle provided at the lower part of the peripheral wall is considered to be about 100 tons.

  The typical radioactive substance content of the contaminated water stored in the tank after the nuclear accident is considered to be around 100,000 Bq / cc, but for safe dismantling of the tank, it is stored from the tank Considering the amount of water remaining after draining the water, it is considered necessary to reduce the radioactive material content of the reservoir water in the tank to, for example, 3,000 Bq / cc or less.

  As an apparatus for removing the contaminants in the tank, an apparatus for removing the contaminants adhering to the inner wall of the tank while moving along the inner wall of the tank has been proposed (see, for example, JP-A-10-2995). . However, in the method using the decontamination apparatus described in this publication, it is not possible to remove radioactive substances dissolved in stored water. In addition, no proposal for a method for decontamination of the tank considering the difficulty of discharging all the water in the tank is found other than the above-mentioned publication.

Japanese Patent Application Laid-Open No. 10-2995

  In view of the above problems, it is an object of the present invention to provide a tank decontamination method capable of efficiently reducing the amount of contaminants in a tank storing contaminated water.

  The invention made to solve the above problems is a method of decontaminating a tank of n groups (n is 2 or more) storing contaminated water, and the k th +1 th tank (k In the case of n, the step of transferring to the first tank or another tank), the step of discharging the contaminated water of the (k + 1) th tank after the transferring step, and the step of purifying by the purification facility, and the purified water after the above purification step The process of introducing into the kth tank so as to abut on the inner surface of the tank, and the process of discharging the stored water of the kth tank after the introducing process into the k + 1st tank or another tank A process for decontaminating a tank is characterized in that the process, the introducing process and the discharging process are repeated from k to 1 to n.

  In the tank decontamination method, after the contaminated water is transferred from the kth tank to be decontaminated to the k + 1st tank, the contaminated water in the (k + 1) th tank is discharged and the purified water purified by the purification facility is removed Introduce so as to abut the inner surface of the tank of the kth tank. Thus, in the tank decontamination method, the total amount of contaminants in the kth tank can be reduced as much as possible in the transfer step, and the amount of water stored in the (k + 1) th tank can be increased. The small amount of contaminated water in the second tank can be diluted with a large amount of purified water, and the concentration of contaminants in the kth tank can be efficiently reduced. In addition, since the contaminant adhering to the inner surface of the tank can be washed out in the introduction step, the k-th tank can be more reliably decontaminated. Further, in the method of decontaminating the tank, the worker does not have to work in the tank, so the concentration of contaminants in the water in the k-th tank can be safely reduced. In the tank decontamination method, the stored water in the kth tank whose contaminant concentration has been reduced in the introducing step is discharged to the kth + 1st tank in the discharging step, whereby contamination in the kth tank is caused. The total amount of substance can be reduced sufficiently. Furthermore, in the tank decontamination method, decontamination of all n tanks can be performed reliably and efficiently by repeating the transfer step, the purification step, the introduction step, and the discharge step from k to 1 to n. .

  In the decontamination of the k-th tank, the transfer step, the purification step, and the introduction step may be repeated several times. As described above, by repeatedly performing the transfer step, the purification step, and the introduction step a plurality of times in the decontamination of the k-th tank, the concentration of contaminated water remaining in the k-th tank is high, and the limit water amount that can be discharged is large. Also in some cases, the contaminant concentration in the k th tank can be reduced to the desired level, which in turn reduces the total amount of contaminants remaining in the k th tank to below the desired value after the draining step. it can.

  The kth tank and the (k + 1) th tank are connected by a connecting pipe, and with the connecting pipe closed, the transferring step from the kth tank to the (k + 1) th tank and the above transferring step to the kth tank It is good to carry out the introduction process. As described above, when the kth tank and the (k + 1) th tank are connected by the connecting pipe, the above-described transfer process from the kth tank to the (k + 1) th tank with the connecting pipe closed. By performing the above-mentioned introduction step to the k-th tank, it prevents the contaminated water from flowing into the k-th tank to be decontaminated from the connecting pipe, and ensures the concentration of contaminants in the water in the k-th tank And the total amount of contaminants remaining in the k th tank can be reliably reduced.

  In the step of introducing the purified water into the k-th tank, the purified water may be introduced through a washing nozzle disposed in the k-th tank. As described above, in the step of introducing purified water to the k-th tank, the purified water is sprayed through the washing nozzle disposed in the k-th tank to efficiently remove the contaminants adhering to the inner surface of the tank. I can wash it out well.

  As the cleaning nozzle, it is preferable to use a three-dimensional cleaning nozzle capable of automatically changing the injection direction of the purified water by 360 °. As described above, by using the three-dimensional cleaning nozzle capable of automatically changing the injection direction of the purified water by 360 °, it is possible to eliminate the washing residue by automatically spraying the purified water on the entire inner surface of the tank. it can.

  The contaminated water preferably contains at least radioactive strontium, and the purification facility preferably has an adsorbent that selectively adsorbs strontium. As described above, when the polluted water contains at least radioactive strontium, the purification equipment can efficiently remove radioactive strontium by having an adsorbent which selectively adsorbs strontium. Here, "selectively adsorbs strontium" means having high adsorption performance to strontium even in the presence of other elements such as calcium and magnesium.

  It is preferable that the above-mentioned purification equipment has an adsorption tower filled with an adsorbent that adsorbs a contaminant, and the adsorption tower be mounted on a movable frame. As described above, the purification equipment has an adsorption tower filled with an adsorbent that adsorbs a contaminant, and the adsorption tower is mounted on a movable gantry, which facilitates the movement of the purification equipment. , The piping distance between the tank and the purification equipment can be short. In addition, a "stand" means the base in which an adsorption tower is arrange | positioned by it, and the plate-shaped or frame-like thing with a small height is included.

  Transfer of contaminated water may be performed using a submersible pump. Thus, the amount of contaminated water remaining in the k-th tank is reduced as much as possible by using the submersible pump to transfer the contaminated water in the transfer step and discharge the stored water in the discharge step. And the amount of contaminants in the kth tank can be efficiently reduced.

  As described above, according to the tank decontamination method of the present invention, the amount of contaminants in the tank storing the contaminated water can be efficiently reduced.

It is a schematic diagram which shows the structure of the decontamination system used for the decontamination method of the tank of one Embodiment of this invention.

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

  The tank decontamination method according to one embodiment of the present invention is performed in the decontamination system having the configuration shown in FIG.

[Decontamination system]
The decontamination system of FIG. 1 discharges the contaminated water in n tanks (n is 2 or more, 4 in the figure) tanks T1 to Tn storing contaminated water, the purification facility R, and the tanks T1 to Tn. And a cleaning nozzle S for injecting water to the inner surfaces of the tanks T1 to Tn.

<Tank>
The tanks T1 to Tn are tanks to be decontaminated in the decontamination method of the tank. The tanks T1 to Tn are not particularly limited. For example, the tanks T1 to Tn are used to store contaminated water containing radioactive materials after a nuclear accident, and are formed by fastening flanges disposed around the periphery of a plurality of plate members with bolts. Bolted tank is assumed.

  In addition, the tanks T1 to Tn are provided in the lower part of the peripheral wall for discharging the liquid inside, and are provided with a discharge flow path D having a valve. The discharge flow paths D of these tanks T1 to Tn are connected to each other by the connecting pipe Lc, and can be connected to other equipment via the connecting pipe Lc.

  Such tanks T1 to Tn are used to store the contaminated water, but after the stored contaminated water is discharged from the discharge flow path D, the contaminated water inevitably remains at the lower inside thereof.

  The lower limit of the amount of the unavoidable residual contaminated water of the tanks T1 to Tn is preferably 1/50 of the volume of the tanks T1 to Tn, and more preferably 1/20. On the other hand, the upper limit of the amount of the unavoidable residual contaminated water of the tanks T1 to Tn is preferably 1⁄4, and more preferably 1⁄5. If the amount of unavoidable residual contaminated water in the tanks T1 to Tn does not reach the above lower limit, the amount of contaminants can be reduced by methods other than the method for decontaminating the tank, which is superior to the method for decontaminating the tank May not be obtained. Conversely, when the water amount of the unavoidable residual contaminated water in the tanks T1 to Tn exceeds the above-mentioned upper limit, there is a possibility that the contaminant concentration in the tanks T1 to Tn can not be sufficiently reduced by the decontamination method of the tank.

  The lower limit of the average inner diameter of the tanks T1 to Tn is not particularly limited, but 3 m is preferable, and 5 m is more preferable. On the other hand, as an upper limit of an average inside diameter of tanks T1-Tn, 25 m is preferred and 20 m is more preferred. When the average inside diameter of the tanks T1 to Tn is less than the above lower limit, the bottom portion is not divided into many, so the drainage limit amount is small, and there is a possibility that the decontamination method can not be advantageous. Conversely, when the average inside diameter of the tanks T1 to Tn exceeds the above upper limit, it may not be easy to bring the purified water into contact with the inner circumferential surface or the ceiling surface of the tank. The "average inner diameter" means an average value of the horizontal minimum dimension in the tank and the horizontal dimension orthogonal thereto.

  Moreover, as a minimum of the average height of tanks T1-Tn, 3 m is preferable and 5 m is more preferable. On the other hand, as a maximum of the average height of tanks T1-Tn, 25 m is preferred and 20 m is more preferred. When the average height of the tanks T1 to Tn is less than the above lower limit, the drainage limit amount with respect to the tank volume becomes small, and the required water amount of the purified water may exceed the tank volume. Conversely, if the average height of the tanks T1 to Tn exceeds the above upper limit, there is a risk that the discharge capacity of the discharge pump P may be insufficient, or washing from an manhole at the top of the tanks T1 to Tn to an appropriate position in the tanks T1 to Tn. There is a possibility that the nozzle S can not be arranged.

  In addition, the contaminated water stored in such tanks T1 to Tn may contain any contaminant as a substance whose concentration is reduced according to the present invention, but typically it is a radioactive substance, in particular It is considered as radioactive contaminated water containing radioactive strontium.

  The contaminant concentration of the contaminated water stored in the tanks T1 to Tn is not particularly limited, and is, for example, 500 Bq / cc or more and 500,000 Bq / cc or less.

<Purification equipment>
The purification facility R is a facility that purifies water supplied from the tanks T1 to Tn, and sends out the purified water to be introduced into the tanks T1 to Tn.

  The purification facility R includes a water receiving tank 11, a supply pump 12, a plurality of filter units 13, a plurality of primary adsorption towers 14, a plurality of secondary adsorption towers 15, a cushion tank 16 and a delivery pump 17.

  The water receiving tank 11 temporarily receives the water supplied from the tanks T1 to Tn. The feed pump 12 pumps water from the water receiving tank 11 to the filter unit 13. The filter unit 13 filters the water supplied from the supply pump 12. In the primary adsorption tower 14, the water filtered by the filter unit 13 is passed through, and the strontium contained in the water is adsorbed in the passed water. The secondary adsorption tower 15 adsorbs other radioactive substances contained in the water that has passed through the primary adsorption tower 14. The cushion tank 16 temporarily receives the water that has passed through the secondary adsorption tower 15, that is, the purified water. The delivery pump 17 pumps the purified water from the cushion tank 16 to the tanks T1 to Tn.

  The water receiving tank 11, the supply pump 12, the filter unit 13, the primary adsorption tower 14, the secondary adsorption tower 15, the cushion tank 16 and the delivery pump 17 are disposed on one or more movable pedestals. Is preferred. As a base on which these components are disposed, for example, it is preferable to be able to move by a forklift or a unit car, or to have a wheel and to be movable by self-propelled or towing. Thereby, since the purification equipment R can be easily disposed in the vicinity of the tanks T1 to Tn, preparation for decontaminating a desired tank is facilitated.

(Water receiving tank)
The water receiving tank 11 is disposed to stably supply contaminated water to the filter unit 13, the primary adsorption tower 14 and the secondary adsorption tower 15 using the supply pump 12.

The lower limit of the capacity of the receiving tank 11, preferably 2m ^3, 3m ³ is more preferable. On the other hand, as a maximum of capacity of water receiving tank 11, 15 m ³ is preferred, and 10 m ³ is more preferred. When the capacity of the water receiving tank 11 does not reach the above lower limit, there is a possibility that the water can not be continuously supplied to the supply pump 12, and the contaminated water may overflow from the water receiving tank 11. On the contrary, when the capacity of the water receiving tank 11 exceeds the above-mentioned upper limit, there is a possibility that portability of purification equipment R may be impaired, and it may become difficult to arrange purification equipment R near tanks T1-Tn.

(Feed pump)
The supply pump 12 is disposed to continuously supply water from the water receiving tank 11 to the filter unit 13, the primary adsorption tower 14 and the secondary adsorption tower 15 at a predetermined pressure. The discharge pressure and the discharge water amount of the supply pump are selected in accordance with the capabilities of the filter unit 13, the primary adsorption tower 14 and the secondary adsorption tower 15.

(Filter unit)
The filter unit 13 filters out suspended solids, oil and the like in the contaminated water. Thereby, the capacity | capacitance fall by the clogging of the adsorbent of the primary adsorption tower 14 and the secondary adsorption tower 15 is suppressed, and the adsorption capacity is fully exhibited.

  The plurality of filter units 13 are preferably connected in parallel so as to allow selective water flow to any one of them, and are disposed so as to be able to replace the entire non-water-flowing filter unit 13 or filters therein.

  For example, a membrane filter having an average opening diameter of about 0.2 μm is suitably used as the filter disposed in the filter unit 13.

  Furthermore, the filter unit 13 preferably has an activated carbon adsorbent layer downstream of the membrane filter. By the filter unit 13 having the activated carbon adsorbent layer, clogging of the adsorbents of the primary adsorption tower 14 and the secondary adsorption tower 15 can be prevented more reliably.

(Primary adsorption tower)
The primary adsorption tower 14 is packed with an adsorbent that selectively adsorbs strontium.

  A plurality of primary adsorption towers 14 are all connected in series, all of which can be water-passed and water-permeable except any one, and the separated primary adsorption towers 14 are replaced with new ones and new ones after replacement It is piping so that the primary adsorption tower 14 can be connected to the most downstream. In this way, it is possible to continuously carry out purification by sequentially replacing the primary adsorption tower 14 whose breakthrough capacity is saturated, ie, the adsorption capacity, with new ones.

  Examples of the adsorbent that selectively adsorbs strontium loaded in the primary adsorption tower 14 include materials having high adsorption performance to strontium even in the presence of calcium and magnesium, such as A-type zeolite and X-type zeolite. Etc. Furthermore, as a preferable adsorbent for selectively adsorbing strontium, it is a capsule-like one having a membrane on its surface which does not permeate calcium and magnesium but selectively transmits strontium and has therein an inorganic material which adsorbs strontium. An adsorbent can be used.

  As a film which selectively permeate | transmits the said strontium, a calcium alginate film etc. are mentioned, for example. Moreover, as an inorganic material which adsorbs strontium, A-type zeolite, X-type zeolite, etc. are mentioned. It is preferable that such a strontium adsorbent be supported on a porous body that also functions as a filter medium for filtering out suspended solids and oil. Examples of such a carrier include activated carbon, zeolite and the like.

(Secondary adsorption tower)
The secondary adsorption tower 15 is packed with an adsorbent that adsorbs radioactive substances other than strontium.

  A plurality of secondary adsorption towers 15 are all connected in series so that all water can be supplied and water can be removed excluding any one, and the separated secondary adsorption towers 15 are replaced with new ones, and new after replacement It is piping so that the secondary adsorption tower 15 can be connected to the most downstream. Thereby, purification can be continuously performed by sequentially replacing the breakthrough (the adsorption capacity is saturated) secondary adsorption towers 15 with new ones.

  As the adsorbent packed in the secondary adsorption tower 15, for example, an adsorbent constituted of titanium oxide carrying cobalt ferrocyanide or iron ferrocyanide, an adsorbent constituted of inorganic carbon and alumina (target to be removed: Adsorbent composed of multiple elements), cesium oxide inorganic material (removal target: Sb, Se, Te, iodic acid), adsorbent composed of activated carbon that supports iodine (removal target: iodine), support tannin Adsorbent composed of activated carbon (target to be removed: transuranic elements (U, np, Pu, Am, Cm)), adsorbent composed of activated carbon supporting reduced iron (target to be removed: Sb, Se, Te, Adsorbents composed of aluminum-containing inorganic carbon materials (targets to be removed: Sb, Se, Te, Tc), various chelating agents (eg DDTC, oxine, DTPA, cuperone etc.) Absorbent composed of activated carbon lifting (removal target: transuranium (U, np, Pu, Am, Cm)) include those containing, and the like. Here, the removal target is "multi-element", and Ag, Cd, Eu, Mn, Co, Y, Ru, Ce, Ni, Zn, Rh, nd, Sn, Sb, Tc, Pr, Sm, Gd, It means that a part or all of V and transuranic elements (U, np, Pu, Am, Cm) are to be removed.

(Cushion tank)
The cushion tank 16 is disposed to supply purified water to the tanks T1 to Tn using the delivery pump 17. The purification facility R may have a mechanism for returning part of the water from the supply pump 12 to the water receiving tank 11 when the water level in the cushion tank 16 rises. By providing this reflux mechanism, it is not necessary to interrupt the purification by the filter unit 13, the primary adsorption tower 14 and the secondary adsorption tower 15 in order to prevent the overflow of the purified water from the cushion tank 16, and the contaminated water purification facility Trouble caused by frequent start and stop can be suppressed.

As a lower limit of the capacity of this cushion tank 16, 2 m ³ is preferable, and 3 m ³ is more preferable. On the other hand, the upper limit of the capacity of cushion tank 16 is preferably 15 m ^3, 10 m ³ are more preferred. If the capacity of the cushion tank 16 does not reach the above lower limit, the purified water may not be continuously supplied to the delivery pump 17 or the purified water may overflow from the cushion tank 16. Conversely, when the capacity of the cushion tank 16 exceeds the above-mentioned upper limit, there is a possibility that portability of the purification facility R may be impaired, or it may be difficult to arrange the purification facility R near the tanks T1 to Tn.

(Delivery pump)
The delivery pump 17 is disposed to supply purified water to the cleaning nozzle S disposed in the tanks T1 to Tn. Purified water is pressure-fed from the delivery pump 17 to the cleaning nozzle S through the supply pipe Ls. The specifications such as the discharge pressure and discharge water volume of the delivery pump 17 take into consideration the pressure loss in the piping and the water head to the height of the tanks T1 to Tn so that the necessary water supply pressure and water supply volume to the tanks T1 to Tn can be obtained To be selected. That is, by providing the delivery pump 17, the purified water can be delivered at a pressure higher than the pressure in the filter unit 13, the primary adsorption tower 14 and the secondary adsorption tower 15. Conversely, if the pressure of the purified water having passed through the secondary adsorption tower 15 is sufficient, the cushion tank 16 and the delivery pump 17 may be omitted.

<Discharge pump>
As the discharge pump P used to discharge stored water from the tanks T1 to Tn, a pump connected to the tanks T1 to Tn via a pipeline can be used, but it is preferable to use a submersible pump . Among them, a well-known low water level discharge submersible pump, which is disposed on the bottom of the tanks T1 to Tn and sucks in and sends out the surrounding water from the lower part, is advantageously used. The discharge pump P is immersed in the storage water by being hung down from the opening at the top of the tanks T1 to Tn with a wire or the like. By using the discharge pump P which consists of such a submersible pump, storage water can be discharged | emitted from the part lower than the opening of the discharge flow path D of tank T1-Tn.

  However, even if the discharge pump P is used, it is difficult to empty the tanks T1 to Tn, in particular when the tanks T1 to Tn are bolted-type tanks, the tank bottom is divided into a plurality of sections by the flanges Even if almost all the stored water in the section where the discharge pump P is disposed can be discharged, the stored water remains in the other sections. In order to empty each section of the bottom of a large tank with a capacity of up to 1000 kL, a worker enters the tank and carries out an operation of disposing a low water pump P in each section of the tank bottom There is a need. However, it is unrealistic for workers to work in tanks with high concentrations of radioactive contaminants. For this reason, the drainage limit amount remaining in the tanks T1 to Tn after discharging the stored water by the discharge pump P depends on the structure of the tanks T1 to Tn, but in the case of a bolted type tank, for example, It is expected to be around 10 tons.

  When the stored water is transferred between the tanks T1 to Tn using the discharge pump P, a transfer pipe Lt is laid between the discharge pump P and the tank of the transfer destination. Further, when the stored water is supplied from the tanks T1 to Tn to the purification facility R using the discharge pump P, an intermediate pipe Lm is laid between the discharge pump P and the purification facility R.

<Cleaning nozzle>
As the cleaning nozzle S, any one that jets purified water pumped from the purification facility R may be used, but it is preferable to use a three-dimensional cleaning nozzle that can automatically change the injection direction of the purified water by 360 °. . By using a three-dimensional cleaning nozzle as the cleaning nozzle S, purified water is sequentially jetted in all directions in the upper, lower, left, and right directions to bring purified water into contact with the entire inner surface of the tanks T1 to Tn. The substance can be washed away. As such a three-dimensional cleaning nozzle, there is commercially available one having a rotation mechanism for rotating the direction of the injection port around two axes orthogonal to each other.

[Decontamination method of tank]
Subsequently, a tank decontamination method according to an embodiment of the present invention performed in the decontamination system of FIG. 1 will be described.

  The method for decontamination of the tank is that after the n tanks T1 to Tn storing the contaminated water as described above, typically, the contaminated water stored therein is discharged from the discharge flow path D, the contaminated water remains This is a method of decontaminating the existing tanks T1 to Tn. More specifically, the method for decontaminating the tank involves cleaning the contaminants adhering to the inner surface of the tank by introducing purified water with reduced contaminant concentration into the tanks T1 to Tn and removing the contaminated water remaining at the bottom of the tank. Dilution is a method suitable for decontaminating the tanks T1 to Tn to such an extent that a worker can work inside the tank after discharging the low concentration contaminated water after dilution.

  The decontamination method of the said contamination tank is the process (transfer process) of transferring contaminated water from the k-th tank to the (k + 1) -th tank (the first tank or another tank when k is n), and after this transfer process And the step of discharging the contaminated water of the (k + 1) th tank and purifying it by the purification equipment R (purifying step) and the step of introducing the purified water after this purifying step into the kth tank so as to abut the inner surface of the tank (introduction step And a step (discharge step) of discharging the stored water of the k-th tank after the introduction step to the (k + 1) -th tank or another tank (discharge step), comprising the transfer step, the purification step, the introduction step and the discharge step. The cycle is repeated from k to 1 to n.

  The transfer step, the purification step and the introduction step may be repeated several times until the contaminant concentration of the stored water in the kth tank falls below the target contaminant concentration in decontamination of the kth tank Good.

  The transfer step, the purification step, the introduction step, and the discharge step are sequentially performed for the first tank T1 for k = 1, that is, for the second tank T2 and subsequent tanks, and for the n-th tank Tn. Repeat in order until done.

  In the transfer step, the cleaning step, the introducing step and the discharging step, the connection pipe Lc connected to the k th tank and the k + 1 th tank is closed, that is, the k th tank and the k + 1 th tank It is performed in the state which closed the valve | bulb of the discharge flow path D. FIG. This prevents the contaminated water from flowing into the k-th tank from the other tank via the connection pipe Lc, and the contaminated water flows out from the (k + 1) -th tank to the other tank through the connection pipe Lc. Can be prevented.

<Transfer process>
In the transfer step, the contaminated water is transferred from the kth tank Tk to be decontaminated in this cycle to the next (k + 1) th tank Tk + 1 using the discharge pump P, that is, the contaminated water is discharged from the kth tank Tk And the next (k + 1) th tank Tk + 1 of the discharged contaminated water is introduced.

  In this transfer step, since the contaminated water is discharged from the kth tank Tk using the discharge pump P, the level height of the remaining contaminated water in the kth tank Tk is lower than the opening height of the discharge passage D It can be done. Thus, in the transfer step, the amount of contaminated water remaining in the k-th tank Tk is reduced as much as possible, and contamination in the k-th tank Tk with a smaller amount of purified water in the introduction step described later Prepare to be able to reduce the substance concentration.

  Also, in this transfer step, the contaminated water discharged from the kth tank Tk is introduced to the next (k + 1) th tank Tk + 1, so the amount of water storage in the (k + 1) th tank Tk + 1 available in the purification step described later can be increased. . Thus, by increasing the amount of purified water obtained in the purification step, that is, the amount of purified water that can be introduced to the kth tank Tk in the introduction step, the number of repetitions of the transfer step, the purification step, and the introduction step can be reduced. It can be reduced.

<Remediation process>
In the above purification process, the contaminated water in the (k + 1) th tank Tk + 1 whose storage capacity has been increased in the transfer process for the kth tank Tk is discharged using the discharge pump P and supplied to the purification facility R, The contaminated water is purified by the purification equipment R to obtain decontaminated water having a reduced concentration of pollutants.

<Introduction process>
In the introduction step, the purified water after the purification step is introduced into the k-th tank Tk via the cleaning nozzle S, thereby washing off contaminants adhering to the inner surface of the k-th tank Tk with the purified water. Contaminated water remaining at the bottom of the k th tank Tk is diluted with purified water. Specifically, in this introduction step, purified water is injected from the cleaning nozzle S, and a jet of contaminated water is sprayed to the inner surface of the kth tank Tk. This introduction step is performed simultaneously and continuously with the above purification step.

  In the decontamination of the k-th tank Tk, the transfer step, the purification step and the introduction step are carried out at the low concentration contamination in which the stored water in the k-th tank Tk, that is, the polluted water initially remaining is diluted by the purified water. It is preferable to carry out repeatedly until the contaminant concentration of water falls below the desired target value.

  Here, whether or not the contaminant concentration of the stored water in the kth tank Tk is equal to or less than the desired target value may be confirmed by sampling and analyzing the stored water periodically, but in advance The introduced amount of purified water and the number of repetitions of the transfer step may be calculated until the contaminant concentration of the stored water in the k-th tank Tk falls below the desired target value. That is, it may be determined that the contaminant concentration of the stored water in the k-th tank Tk has decreased to a desired target value or less when the transfer step, the purification step and the introduction step have been performed the calculated number of times. .

As a method of calculating the number of repetitions of the transfer step, the purification step and the introduction step, the initial contaminant concentration of the contaminated water in the kth tank is Cr [Bq / L], and the contaminant concentration of the purified water is a constant value Cs [Bq / L], the drainage limit amount remaining in the tank after discharge by the discharge pump P is a constant value Vr [L], the water amount of the purified water introduced into the kth tank Tk in one introduction step is Vs Assuming that [L] and the target contaminant concentration is Ct [Bq / L], the number n of repetitions of the transfer step, the purification step, and the introduction step may satisfy the relationship of the following formula (1).
(Cr−Cs) × {Vr / (Vr + Vs)} ⁿ + Cs ≦ Ct (1)

That is, the number of repetitions n of the transfer step is a minimum integer that satisfies the following formula (2).
n ≧ log _{{Vr / (Vr + Vs)}} {(Ct-Cs) / (Cr-Cs)} (2)

  With regard to the concentration of pollutants in purified water, conventionally, when adsorbing and removing pollutants in contaminated water with an adsorbent, it is considered that the removal rate of pollutants is 100% until saturation of the adsorbent, so-called breakthrough occurs. It was being done. However, when the present inventors analyzed the treated water in which the polluted water was adsorbed by the adsorption tower in detail, it was found that the contaminant concentration of the polluted water before the treatment is from the start of use of the adsorbent until breakthrough occurs. In addition, it has been found that the treated water treated with adsorption may have a certain low contaminant concentration. Therefore, a new technical idea has been conceived in which the contaminant concentration of the purified water can be set to a constant value Cs [Bq / L], and the number of repetitions n is determined by the equation (1) or the equation (2).

  Further, the stored water may be transferred from a tank other than the k-th tank Tk to the (k + 1) th tank Tk + 1 before performing the first purification step so that the number of repetitions n becomes 1 in the above equation (2). That is, by increasing the maximum water volume Vs of the purified water that can be introduced into the kth tank Tk in one introduction step, the transfer step, the purification step, and the introduction step may be performed only once each without each repetition. The contaminant concentration of the stored water in the k-th tank Tk may be reduced to the target value or less.

Specifically, in order to set the number of repetitions n to 1, assuming the initial residual contaminated water volume of each tank as Vt, the number of tanks other than the k th tank T k that transfers stored water to the (k + 1) th tank T k + 1 What is necessary is just to let m be the minimum integer which satisfy | fills following formula (3).
m ≧ (Cr-Ct) / (Ct-Cs) x Vr / (Vt-Vr)-1 (3)

<Discharge process>
In the discharge step, the stored water of the k th tank T k whose contaminant concentration has decreased to a predetermined target value or less by repeating the transfer step, the purification step and the introduction step is transferred to the (k + 1) th tank T k + 1 using the discharge pump P Discharge.

  In this discharging step, the stored water in the k-th tank Tk is discharged to sufficiently reduce the total amount of contaminants remaining in the k-th tank Tk, whereby workers in the k-th tank Tk Allows you to do the work.

  The work performed by the worker includes the draining operation of the stored water of the drainage limit amount Vr [L] remaining in the k-th tank Tk after the discharging step and the disassembling operation of the k-th tank Tk.

  Further, in the discharging step, since the stored water discharged from the kth tank Tk is introduced to the (k + 1) th tank Tk + 1 to be decontaminated next, the initial value of the contaminant concentration of the stored water in the (k + 1) th tank Tk + 1 is decreased. be able to. Therefore, it is possible to reduce the number n of repetitions of the transfer process, the purification process and the introduction process in the next cycle.

  When the total amount of stored water drained from the k-th tank Tk in the discharging step is introduced into the (k + 1) -th tank Tk + 1, the initial water storage amount of the k-th tank Tk increases whenever k increases. Increasing the initial value of the storage volume of the k-th tank Tk more than necessary may cause decontamination to be inefficient due to the increase in water volume, or may cause contaminated water to overflow from the (k + 1) -th tank Tk + 1 in the transfer step. There is. For this reason, in the discharging step, part of the stored water may be discharged to another tank other than the (k + 1) th tank Tk + 1.

  As described above, according to the tank decontamination method, the amount of contaminants in the tank storing the contaminated water can be efficiently reduced.

Other Embodiments
The above embodiment does not limit the configuration of the present invention. Therefore, the above-mentioned embodiment can omit, substitute or add the components of each part of the above-mentioned embodiment based on the description of the present specification and technical common sense, and all of them are interpreted as belonging to the scope of the present invention It should.

  As an example, the contaminated water stored in the tank to be decontaminated by the method of decontaminating the tank may contain any contaminant. In addition, the contaminant concentration may be represented using any index, and can be represented by, for example, mass concentration, molar concentration, pH, radioactivity and the like.

  In the tank decontamination method, the cleaning nozzle may not necessarily be used when introducing the purified water into the k-th tank. Further, it is not necessary to bring the purified water introduced into the entire inner surface of the k-th tank into contact with the entire inner surface of the k-th tank.

  Moreover, you may decontaminate the tank which is not mutually connected by the connection pipe in the decontamination method of the said tank.

  In the tank decontamination method, transfer and discharge of contaminated water may be performed using means other than a pump. Also, the type of pump used in each process may be different. However, in particular, the transfer of the contaminated water in the transfer step is preferably performed using a submersible pump in order to effectively reduce the amount of contaminants in the tank.

  In addition, the purification equipment used in the method for decontamination of the tank may be anything that can purify the contaminated water remaining in the tank to be decontaminated, and may not use an adsorbent. In addition, the purification facility may be configured by assembling the respective components in place without having a movable mount.

  The present invention can be used to decontaminate various tanks, but is suitably used to decontaminate a tank for storing contaminated water, particularly containing radioactive substances.

D Discharge flow path Lc Connection pipe Lm Intermediate piping Ls Supply piping Lt Transfer piping P Discharge pump R Decontamination equipment S Cleaning nozzle T1, T2, T3, T4 Tank 11 Water tank 12 Supply pump 13 Filter unit 14 Primary adsorption tower 15 2 Next adsorption tower 16 Cushion tank 17 Delivery pump

Claims (8)

Decontamination method of n (n is 2 or more) tanks storing radioactive contaminated water,
Transferring radioactive contaminated water from the k th tank to the k th +1 th tank (the first tank if k is n ) ;
After the transfer step, the radioactively contaminated water in the (k + 1) th tank is discharged and purified by the purification facility;
Introducing the purified water after the purification step into the kth tank so as to abut the inner surface of the tank;
Discharging the stored water of the kth tank after the introduction step to the (k + 1) th tank or another tank;
A method of decontaminating a tank, wherein k is repeated from 1 to n in the transfer step, the cleaning step, the introducing step and the discharging step.
  The method for decontaminating a tank according to claim 1, wherein the step of transferring, the step of purifying, and the step of introducing are repeated a plurality of times in the decontamination of the k-th tank.   The kth tank and the (k + 1) th tank are connected by a connecting pipe, and with the connecting pipe closed, the transferring step from the kth tank to the (k + 1) th tank and the above transferring step to the kth tank The method for decontaminating a tank according to claim 1 or 2, wherein the introducing step is performed.   The tank according to claim 1, 2 or 3, wherein in the step of introducing purified water to the k-th tank, the purified water is introduced through a washing nozzle disposed in the k-th tank. Decontamination method.   The method for decontaminating a tank according to claim 4, wherein a three-dimensional cleaning nozzle capable of automatically changing the injection direction of the purified water by 360 ° is used as the cleaning nozzle. The method for decontamination of a tank according to any one of claims 1 to 5, wherein the radioactively contaminated water contains at least radioactive strontium, and the purification facility has an adsorbent which selectively adsorbs strontium.
  The said purification | cleaning installation has an adsorption tower packed with the adsorption agent which adsorb | sucks a contaminant, and this adsorption tower is mounted in the movable stand which can be moved according to any one of the Claims 1-6. How to decontaminate the tank. The method for decontaminating a tank according to any one of claims 1 to 7, wherein the radioactively contaminated water is transferred using a submersible pump.

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